Global nutritional problems with special attention to the role of animal foods in human nutrition

P. Pellett and S. Ghosh
Department of Nutrition, School of Public Health and Health Sciences
University of Massachusetts
Amherst, Massachusetts 01003, USA

Introduction

Although cereals have become the major source of food energy and protein in the world since the development of agriculture, animal foods—milk, meat, fish and eggs, as well as foods originating from non-vertebrates—have been consumed in all societies throughout human history. Quantities and proportions vary enormously among cultures, and consumption levels are conditioned by traditional, religious, social, climatic and economic factors. These factors are more the concern of geography, anthropology, sociology and other sciences than of nutrition, but they have had enormous nutritional implications. In this review, the nutritional implications of animal food consumption are central to the discussion.

Health has been defined by the World Health Organization as a state of complete physical, mental and social well being and not merely the absence of disease and infirmity. It is also described as a fundamental human right, whose realisation requires the action of many other social and economic sectors in addition to the health sector. Good nutrition is an essential component for optimal health. Deficiencies in foods and nutrients were originally perceived as the major factors causing malnutrition (Lusk 1928). It is only in more recent times that a number of fundamental interactions have been recognised and that the importance of infection, disease, water and sanitation in causing malnutrition has been emphasised.

Factors that affect nutritional status, in addition to nutrient supply and nutritional needs, now include health status, which involves consideration of sanitation, infections and infestations together with the availability of health services. More recently, the roles of the family and the community in nutritional care have been formally recognised. Key global priorities, as defined by the International Conference on Nutrition (FAO/WHO 1992), now include nutritional care for the vulnerable, increased household food security, reduced micronutrient deficiencies, improved food quality and safety, and the availability of healthy diets, as well as national and international nutritional monitoring and surveillance.

The global nutrition situation

Currently, 760 million people in the developing world are chronically undernourished and 192 million children suffer from protein-energy malnutrition. In addition, an estimated 2 billion adults and children suffer from micronutrient deficiencies (FAO/WHO 1992). Diet-related chronic diseases such as cardiovascular disease are a new problem in some developing countries, as activity and dietary patterns change and smoking continues to increase. Despite these large numbers of the malnourished and the humanitarian tragedy that they represent, some progress is being made. The numbers and percentages of the undernourished have dropped from 920 million (35%) in 1969-71 to 8100 million (20%) in 1990-92. These data, together with the Food and Agriculture Organization (FAO) projections for 2010, are illustrated in Table 1.

Table 1. Number and proportion of undernourished.

	Number (millions)	Percentage
1969-71>	920	35
1990-92	8100	20
2010	680	12

Undernourished are defined as below the population specific threshold for light activity.
Source: FAO (1996b).

The availability of dietary energy worldwide is also increasing, albeit slowly, and infant mortality rates have declined, although they are still unacceptably high in poorer countries. There have been significant decreases in the under-5 mortality rates in all regions of the world in the past 30 years (Table 2). The proportional decreases for developing and least developed countries have, however, been much less than for industrialised countries.

Table 2. Comparison of number of deaths below the age of 5 years per 1000 live births in 1960 and

1995.
Year	Industrial	Developing	LDCs1
1960	37	216	283
1995	8	99	173

1. LDCs - less-developed countries.
Source: UNICEF (1997).

Despite progress, the numbers are still alarming, and hunger and malnutrition remain the most devastating problems in the world today. Poverty is the major determinant and conditions associated with malnutrition are most prevalent in the less wealthy regions of the world. Under-5 mortality rates and the percentages of children with low birth weight (LBW), which are indicators of malnutrition, are highest in countries with a low GNP (Table 3). The most affected are in the least developed countries (LDCs), numbering nearly 600 million in all, whose per capita GNP averages less than US$ 1 per day.

Table 3. Wealth and health data.

Country category	Total population (millions)	GNP(US$)	U5 MR	Low birth weight(%)	Life expectancy(years)
Industrial	830	24,300	8	6	77
Developing	4526	1,023	99	19	62
Less developed	586	233	173	23	52

Source: UNICEF (1997).

The number of wasted, stunted and underweight children is also highest in low-income countries (Table 4). South Asia has the largest proportion and the highest numbers of malnourished children (Table 5), followed by East and South-East Asia, with the Middle East-North Africa and Latin America being relatively less affected. Nutritional problems are not restricted to the children in these areas; undernutrition is also prevalent in adolescents and adults in many developing countries. From FAO estimates, 12.5% of the Chinese population and 48.6% of the Indian population have body mass index (BMI) values (wt/ht2) below 18.5, which is considered the lower limit of normality.

Table 4. Estimates of the number of wasted, stunted and underweight children under 5 years of age in different economic classes in developing countries.

	Wasted		Stunted		Underweight
Economic class	%	Millions	%	Millions	%	Millions
Low	10.3	100	45.2	174.4	38.2	147.6
Middle and high	5.6	8	28.7	100.8	22	31.2
Total	9.1	47.9	100.7	215.2	33.9	178.8

Source: FAO (1996b).

Table 5. Estimates of the number (millions) and percentage of wasted, stunted and underweight children under 5 years of age by region.

The most vulnerable population groups are women, infants and children. In absolute terms, because of their small body size, infants have the lowest requirements for energy, protein and other nutrients, but the greatest requirements per unit of body weight, because of the rapid growth that occurs during this phase. With increasing age, the absolute requirement increases.

The causes of malnutrition

Only in relatively recent years have the causes of malnutrition been seriously discussed and factors that lie beyond the immediately obvious considered. As illustrated in Table 6, determinants of malnutrition can be recognised at three key levels—the immediate, the underlying, and the basic causes (UNICEF 1990; Jonnson 1995).

Table 6. Levels of determinants of malnutrition.

Immediate causes

Food intake and health

Underlying causes

Income, land, education, water, fuel, health service availability

Basic causes

Resources, economics, politics

Source: Adapted from UNICEF (1990).

Nutritionists have in the past limited themselves to discussing the immediate causes, mainly the lack of food or nutrients, and have been less concerned with underlying and basic causes. Immediate causes, nonetheless, should also include the health status of the individual. Decreased intake, absorption or utilisation, increased losses through diarrhoea or increased requirements such as in pregnancy and lactation are all significant. Any of these immediate causes could lead to depletion of essential nutrients. This depletion in turn is affected by income, education and the availability of water and sanitation, which themselves are determined by politics and economics.

Specific deficiencies of energy, protein, essential amino acids, vitamin A, iodine and iron, considered to be the most widespread, have been found to be associated with malnutrition and growth impairment (FAO/WHO 1992). More recently, the roles of zinc and copper in growth and their possible limitation in diets in developing countries have been given greater recognition.

The major underlying causes of malnutrition include poor food production or supply; poor food distribution, both between families and within families; poor education; and finally, poor sanitation and health. The latter consideration, linking malnutrition to health and the environment, including infectious disease, was itself a major breakthrough and resulted from a review article on the interactions between nutrition and infection (Scrimshaw et al 1968). The review demonstrated conclusively that a wide range of factors beyond mere food or nutrient availability could precipitate malnutrition. The interaction between malnutrition and infection is complex, but the rather simplistic circular approach illustrated in Figure 1 can be used to demonstrate the relationships.

Figure 1. The relationships between malnutrition and infection.

The basic causes of malnutrition, however, remain related to poverty, as a consequence of the uneven distribution of resources brought about by worldwide economic and political forces (UNDP 1996). There are very large differences in food availability and dietary patterns between rich and poor countries. Rich countries have more food energy available per capita and also consume higher levels of protein, especially of animal origin. These dietary differences are accompanied by large differences in the availability of water, sanitation and health care.

Anthropometric criteria for nutritional assessment

Nutritional assessment can be defined as the interpretation of information obtained from dietary, biochemical, anthropometric and clinical studies. Assessment is used to determine the health status of individuals or population groups as influenced by their intake and utilisation of nutrients. The whole field of clinical and biochemical assessment has been extensively reviewed by Heymsfield and Williams (1988). Such individual assessment is far more complex and time consuming than is generally possible for within-country field activities. Major methods available for field surveys are divided into two key categories: those that are food related and those that are health or people related. The latter includes the major assessment technique of anthropometry.

Anthropometric indices provide measurable reflections of nutritional status and can help differentiate between chronic and acute malnutrition or stunting and wasting. The indicators most often used are body weight and height, in relation to age and sex. Other, less frequently used indicators include arm, head and thigh circumferences and skin-fold thickness. The main anthropometric indices used for children are weight-for-height, height-for-age and weight-for-age. Body Mass Index (BMI) is the main index used for adults and is defined as the weight in kilograms divided by the square of height in metres. The World Health Organization (WHO) uses data of the National Center for Health Statistics (NCHS), USA, as a reference standard, since many studies have shown that the growth of normal, healthy and adequately nourished children almost always approximates these reference values irrespective of racial or genetic background. Previously, anthropometric data for children were reported as percentages of the reference median but now they should be quoted in ‘Z-scores’, based on standard deviations (SDs) above or below the median reference value for a person of a given age (WHO 1986, 1995). At any age the level of median minus 2 SDs is usually taken as the threshold below which undernutrition exists.

Weight for height

The weight-for-height index is used for both adults and children in relation to accepted reference values. In the acutely undernourished, those who have had inadequate dietary intakes or an acute infection within recent weeks, decline in body weight is relatively rapid, but height remains unchanged in adults and changes very slowly in children. Weight for height is a measure of acute undernutrition or wasting and is the index most used in nutritional emergencies as well as for long-term situations of undernutrition, such as famine. In children, weight-for-height data can be used to assess malnutrition without accurate knowledge of the individual’s age.

Height for age

The height-for-age indicator is used for assessing chronic undernutrition in children. Prolonged undernutrition causes retardation of growth in both height and weight to a roughly comparable degree. Impaired height gain is called ‘stunting’. Height gain is most affected by long-standing environmental and socio-economic factors; hence, it reflects general socio-economic conditions.

Weight for age

The proportion of children under five years of age in many developing countries who are below the weight-for-age reference median minus 2 SDs ranges from 10% to 100%, with an average of around 20% to 30%. The weight-for-age indicator is often easier to determine and is hence more readily available than weight for height or height for age. It can, however, be more difficult to interpret because it is a consequence of either acute or chronic undernutrition or, indeed, of both.

Present procedures for using the above indicators and for evaluating results obtained with them were prescribed following a major survey in Egypt (USAID 1978), which involved 8600 children from the whole country. According to the usual criteria for malnutrition, 47% were considered malnourished using weight for age, 22% using height for age, but only 3% when using weight for height. Body-size adaptation to poor nutrition and poor health was recognised, and many arguments developed as to how many children were really malnourished and who were those at most risk. Currently we usually assess malnutrition by using all three criteria and base action accordingly. Highest priorities for action are given for acute malnutrition, i.e., those with weight to height that is more than 2 SDs below the median. If 5-10% of the population group is below this level, the degree of acute undernutrition may be described as moderate; if the proportion is more than 10%, the situation is generally considered severe.

In developing countries, widespread chronic undernutrition (stunting) is common. The proportion of individuals below the median minus 2 SDs is often in the range of 20% to 60%, with an average near 100%. Populations in which height for age of 25% to 100% of the children under five is 2 SDs below the median are commonly considered to be moderately affected while those with more than 100% are considered severely affected.

Body-mass index

Body-mass index, or BMI, provides a measure of body mass ranging from thin to obese. A proposed classification for body-mass index for adults is shown in Table 7. There is no firm agreement on the cited cut-off points and discussion continues. Despite the ongoing arguments (FAO 1994; James 1994) involving the validity of the index, causes of low BMI and the cut-off levels to be used, there is general agreement that adults with low BMI generally have lower work capacity and limited social activity. They also generally have lower incomes and more sickness, and women have a higher proportion of LBW babies.

Table 7. A proposed classification using body mass index (BMI, weight in kg/height² in m).

Chronic energy deficiency, Grade 3	<16.0
Chronic energy deficiency, Grade 2	16.0-16.9
Chronic energy deficiency, Grade I	17.0-18.4
Normal	18.5-24.9
Overweight	25.0-29.9
Obese	30.0-100.0
Morbidly obese	>100.0

Source: USDHHS (1988) for normal and obese: for normal and for chronic energy deficiency from James (1994) and FAO (1994).

Validity considerations include consideration of cut-off levels and sex specificity, whether the cut-off levels should be age dependent, whether there are cultural or ethnic differences in body composition and energy stores and also whether there are a number of other important interactions (FAO 1994; James 1994).

Severe adult undernutrition, now termed ‘chronic energy deficiency’ (CED), is of major consequence worldwide and can be assessed by the use of BMI. Some of the causes of chronic energy deficiency are inadequate food energy intake, though care should be taken to note whether there are significant seasonal variations in energy availability. Anorexia from intestinal parasites together with chronic infection and trace element deficiencies can also cause CED.

Global nutrient distribution

Source: Adapted from FAO (1996a).
Figure 2. Population and nutrient distribution in developed and developing nations.

Disparity in the availability of food and the dietary patterns between the rich and poor, especially when associated with different health conditions, is a major cause of malnutrition. In Figure 2, distributions of population and of selected nutrients are depicted for developed and developing nations.

Seventy- six per cent of the world population lives in the developing regions. In terms of nutrient distribution, however, 29% of total food energy is available to developed areas as compared with 71% in developing areas. Total protein availability is higher at 34% for the developed areas compared with 66% for the developing areas; total lysine and fat availability are 41% and 43%, respectively, for the developed areas, leaving only 59% and 57% for the much larger population of the developing areas.

Dietary energy supply (DES) has always been higher in developed countries. In the late 1960s, their average food energy supply was 3190 kcal/day, compared with 21100 kcal/day in the developing world. Since then there has been an increase in both groups. Because the level was already more than adequate in the developed regions, the rate of increase has been much higher for the developing world, but, as illustrated in Table 8, a gap still exists between the two. More detailed information for regional groupings is shown in Table 9.

Table 8. Per capita dietary energy supply (kcal/day) for developed and developing countries in 1969-71, 1990-92 and estimated for 2010.

33100

Region	1969-71	1990-92	2010
Developed	3190		3390
Developing	21100	2520	2770
World	24100	2720	2900

Source: FAO (1996a).

Table 9. Per capita dietary energy supply by region in 1969-71 and 1990-92.

Region	1969-71	1990-92
Latin America and Caribbean	2510	27100
Sub-Saharan Africa	21100	20100
Near East and North Africa	2380	2960
East and South-East Asia	2060	2680
South Asia	2060	2290

Source: FAO (1996a).

Developed countries have a greater availability of per capita DES and of total protein, lysine and fat (Figure 2) and a much greater proportion of the protein is animal in origin (Table 10). Although there has been a significant increase in the total protein supply for both developing and developed areas, a great difference remains in the total amount available. For the developed countries more than 100% of the total protein was of animal origin in both 1969-71 and 1990-92. For the developing areas, however, animal protein is a much smaller portion of the total protein supply (Table 10).

Table 10. Total protein and animal protein supplies (g/capita per day) by region in 1969-71 and 1990-92.

	Total protein		Animal protein
Region	1969-71	1990-92	1969-71	1990-92
Developed	95	102	51	59
Developing	53	62	10	15
World	65	71	22	25

Source: FAO (1996a).

Source: Adapted from FAO (1996a).
Figure 2. Population and nutrient distribution in developed and developing nations.

Animal protein in the diet is important, as it is usually highly digestible and provides higher levels of essential amino acids, especially lysine, as well as useful levels of several micronutrients in highly bioavailable forms. The distribution of protein from various food groups, calculated using data from FAOSTAT (1996) for Syria, the USA and the world for 1994, is shown in Figure 3. There is a clear difference in the apparent consumption of cereals and animal foods between Syria and the USA. Cereals contribute a much larger percentage of protein (approximately 65%) in the Syrian diet. In contrast, animal foods including meat, fish, milk and eggs make up approximately 70% of the total protein in the American diet.

Figure 4 shows the major sources of protein in Syria from1961 to 1994. Cereal protein consumption has increased over the years, the increase being marked from the early 1980s. Animal protein availability, while increasing steadily until the early 1980s, has since declined. As a result of these changes, the estimated average lysine availability for Syria increased from about 2700 mg/day in 1961 to 3900 mg in the early 1980s and then declined to about 3300 mg/day in 1994.

The pattern for the per capita supply of fat is similar to that of protein. Developed countries had more than twice as much fat available per capita compared with developing countries in both 1969-71 and 1990-92 (Table 11). Developing countries had much lower levels of available animal fat, which, although higher than in 1969-1971, were still only 26% of the level of developed countries. The disparity is much sharper with respect to protein and fat supplies than energy, because foods that are rich in protein and fat are normally more expensive than basic energy-rich foods.

Table 11. Total fat and animal fat supplies (g/capita per day) by region in 1969-71 and 1990-92.

	Total fats		Animal fat
Region	1969-71	1990-92	1969-71	1990-92
Developed	108	125	68	73
Developing	33	51	12	19
World	55>	69>	28	32

Source: FAO (1996a).

Source: FAOSTAT (1996).
Figure 4. Major sources of protein Syria: 1961-1994.

The dietary role of animal foods

Animal foods contribute significantly to the protein and fat in the diet. Legumes are also a major source of dietary protein, but the nutritional quality of animal protein is superior to that of cooked legumes because of the somewhat better balance of essential amino acids (Pellett and Young 1988, 1990; Briggs and Schweigert 1990; Young and Pellett 1990). Animal foods also provide significant quantities of vitamins, including the B-complex vitamins, vitamins A, D, E and K, and minerals such as calcium, copper, iron, manganese and zinc. Usually these are in a highly bioavailable form. There are a number of major nutritional advantages as well as some disadvantages in the consumption of animal foods, as shown in Table 12.

Table 12. Advantages and disadvantages of animal foods in the diet.

Advantages	Disadvantages
Highly desired and digestible	High in saturated fat and cholesterol
Good quality protein	Low levels of complex carbohydrates and fibre
Highly bioavailable micronutrients	Expensive and perishable
Small amounts required to nutritionally transform cereal-based diets	High cost of production
Good source of fat in the diet

Animal foods are highly digestible and contain protein that is usually, but not always (hair, skin and connective tissue are exceptions) of high nutritional quality. They contain good levels of all the essential amino acids and are significantly higher than most other foods in their content of lysine. They are, however, low in complex carbohydrates and fibre and high in cholesterol and saturated fat, which can be a problem in developed countries, with an increased risk of cardiovascular and other nutritionally related chronic diseases.

For many people in developing countries, animal products do not contribute significantly to the diet and hence to the risk of chronic diseases due to overconsumption of animal fat. Problems lie more in the lack of fat in the diet, since lipids are required for a number of important metabolic and physiological functions as well as being a source of energy. Some of these functions are shown in Table 13. Fat is involved in cell structure and hormone production, as well as being a source of cholesterol for hormones and essential fatty acids, required for the production of prostaglandins. Fat-soluble vitamins A, D, E and K are better absorbed in the presence of fat. Fat also makes food more palatable and increases the energy density of the diet. Body fat deposits insulate and cushion important organs and are a readily available energy store.

Animal foods are, however, expensive and often perishable. Their production often means that the animal has to consume large amounts of food energy to build body tissue. Only very small amounts of food of animal origin, however, are required to improve the nutritional quality of cereal-based diets.

Table 13. Importance of fat in the diet.

Energy, structural and hormonal roles

Source of essential fatty acids (linoleic, linolenic and arachidonic) and cholesterol

Vehicle for fat-soluble vitamins A, D, E and K

Increases palatability of food

Provides high-energy density

Insulation, cushion and energy store in body

Protein and essential amino acids

The role of protein in the diet cannot be overemphasised, since protein is the basis of life. Protein deficiency along with energy deficiency has been recognised for more than a century as a major nutritional problem in the world. Since 1936, a number of international groups, including the League of Nations, FAO, WHO, the United Nations University (UNU) and the International Dietary Energy Consultative Group (IDECG), have made recommendations on the protein requirements of infants, children and adults (Pellett 1990).

Protein requirement is defined by the FAO/WHO/UNU (1985) group as ‘the lowest level of dietary protein intake that will balance the losses of nitrogen from the body in persons maintaining energy balance at modest levels of physical activity. In children and pregnant or lactating women, the protein requirement is taken to include the needs associated with the deposition of tissues or the secretion of milk rates consistent with good health.’ Recommendations on protein requirements for children have changed significantly over the years. In 1953, 3-4 g/kg per day of protein were recommended for children between about six months and three years of age (NAS-NRC 1953), whereas now the recommended level is about 1 g/kg per day (IDECG 1996). These changes have significantly affected views on the causes of child malnutrition in developing countries.

Besides total protein requirement, protein quality and hence essential amino acid requirements are also important. There is evidence that lysine may be the key limiting amino acid in the human diet (Young et al 1989; FAO/WHO 1991; Pellett 1996) and lysine intakes have been shown to be the most variable of all the essential amino acids, whether expressed as milligrams per gram of food protein or as milligrams per day (Pellett and Young 1990; Pellett 1996).

Lysine levels vary with the composition of the diet and are positively correlated with the amount of animal protein present. Cereals, which are the major source of food energy and protein in many of the diets of the developing world, are not a good source of lysine (Young and Pellett 1994). Legume proteins, however, are good lysine sources.

Table 14 shows that the availability of total food energy, total protein, animal protein and lysine increases with an increase in GNP. Average daily lysine values differ considerably between the richest and the poorest groups. At the same time, child mortality rates decline. No direct correlation between mortality rates and diet is implied, but both are significantly correlated with wealth. Between 1961 and 1994, lysine levels in Syrian diets first rose and then fell, corresponding to the decrease in animal protein and the steady increase in cereal protein (Figure 4) over that period.

Table 14. Total population, nutrient availability, mortality rate, and life expectancy in relation to economic class (data from 122 countries world-wide).

GNP class US$ per person per year	Coun-tries (no.)	Total popn.(millions)	Food energy (kcal/d)	Total protein (g/d)	Animal protein (%)	Cereal protein (%)	Pulsesoy protein (%)	Lysine (mg/d)	Lysine (mg/g protein)	Lysine (mg/103 kcal)	Under 5MR1	Life expc2 (yr)
<1000	37	2990	2070	51	20	53	11.4	21005	47	1174	171	52
1000-2,000	41	862	2570	65	31	100	7	3270	100	1268	76	64
2,000-10,000	21	548	2913	78	>45	39	5.6	4484	58	1544	39	69
>10,000	23	806	3335	101	61	24	2.7	6555	65	1966	9	77

1. Number of deaths below the age of 5 years per 1000 live births.
2. Life expectancy in years at birth.
Source: Pellett (1996).

A number of options exist for increasing the lysine value of cereal-based diets, including increasing the amounts of cereals consumed, consuming greater amounts of foods high in lysine and fortifying with the synthetic amino acid. The latter procedure is frequently used for animal feeds in the developed regions of the world. The first option is often not feasible, as people may not be willing or able to eat the extra bulk of food. This is especially true of young children, who have small somachs.

The option of increasing the availability of animal foods will be highly constrained by social and economic factors. Only small quantities, however, are required to improve quality, which may be economically possible. Lysine can be added in synthetic form, together with micronutrients, to improve the quality of the protein, especially with wheat-based diets where flour is centrally milled.

Micronutrient deficiencies

The most prevalent micronutrient deficiencies are iron, affecting over 2 billion people; iodine, affecting 1 billion; and vitamin A, affecting 100 million (FAO/WHO 1992). More recently, zinc and copper deficiencies have been identified as being of greater importance in children than was previously considered. Zinc deficiency in diets with low levels of animal protein may increasingly become a major public health problem. Allen (1994) has extensively reviewed the role of these and other micronutrients in growth faltering.

Iron

Iron-deficiency anaemia is a major problem worldwide, especially in women and children (Table 15). Both low iron intakes and the lack of factors such as vitamin C that enhance the utilisation of non-haem iron contribute to deficiency. The absorption of non-haem iron from most foods is poor, sometimes as low as 2%. Only animal foods, especially meat products, provide haem iron, of which 20-30% is absorbed. Table 16 shows the iron content of selected foods.

Table 15. Prevalence of anaemia and iron deficiency in the world.

WHO region	Number of anaemic or iron deficient people (millions)	revalence of anaemia in pregnant women (%)
Africa	206	52
Americas	94	100
Europe	27	18
Eastern Mediterranean	149	100
South-East Asia	616	74
Western Pacific	1058	100
Developed countries	na1	18
Developing countries	na	56
Total	21100	51

1. Figures not available.
Source: WHO/UNU/UNICEF (1993).

Anaemia in children and infants may retard physical and cognitive development. In adults it can cause fatigue, reduce work capacity and impair reproductive function. In pregnancy it is associated with reduced foetal growth, low birth weight, and greater perinatal mortality. Twenty per cent of maternal deaths may be associated with anaemia as it predisposes to haemorrhage and infections (FAO/WHO 1992). The role of iron in the growth and development of children has been extensively studied. Improved weight gain in infants and children under 3 years of age has been observed (Aukett et al 1986). Indonesian children showed increased height and weight when their diet was supplemented with iron for 12 weeks (Chwang et al 1988). Kenyan children showed improved weight and appetite though no increase in height (Latham et al 1990).

Table 16. Iron content (mg/100 g of edible portion) of selected foods.

Food	Total iron	Haem iron	Non-haem iron1
Beef	2.62	1.05	1.57
Lamb	1.88	0.75	1.13
Liver	6.82	2.73	4.09
Chicken	1.17	0.47	0.7
Crab	0.59	0.23	>0.36
Milk	0.05	-	0.05
GLV	2.71	-	2.71
Rice	4.36	-	4.36
Wheat flour	3.88	-	3.88
White flour	1.17	-	1.17

1. Calculated by the method of Monsen et al (1978).
Source: USDA (1976-1994).

Vitamin A

At least 190 million children (Table 17) live in areas where consumption of foods containing vitamin A is low (FAO/WHO 1992). Of these, 100 million are deficient in available vitamin A and 14 million have clinical signs of deficiency. Every year a quarter to half a million children become partially or totally blind due to vitamin A deficiency. Two-thirds of these children die within a few months of becoming blind. Vitamin A deficiency reduces resistance to infection, causes night blindness and eventually xerophthalmia, affects physical growth and increases morbidity and mortality in children (FAO/WHO 1992).

Table 17. Population (millions) at risk and affected by vitamin A deficiency.

Region	At risk	Affected (xerophthalmia)
Africa	18	1.3
Americas	2	0.1
South-East Asia	138	10
Europe	-	-
East Mediterranean	13	1
Western Pacific	19	1.4
Total	190	13.8

Source: FAO/WHO (1992).

Vitamin A is fundamental to the development and function of tissues and plays an important role in cellular differentiation, in the immune system and in vision. Vitamin A deficiency is caused not only by the low content of retinol or beta-carotene or both in the food supply but also by their low absorption and utilisation. In addition, diarrhoeal and respiratory diseases can precipitate deficiency. Vitamin A is present as retinol in animal foods but as beta-carotene in plant foods. Beta-carotene is less efficiently absorbed than the retinol from animal foods. Most of the population in developing countries obtain their vitamin A from plant foods.

Associations between linear growth stunting and night blindness or xerophthalmia have been demonstrated (Brink et al 1979; Muhilal et al 1988; Mele et al 1991). Indonesian children with subclinical vitamin A deficiency showed improvements in linear growth when their diet was supplemented with vitamin A (Muhilal et al 1988). Rahmathulla et al (1991), however, reported no improvement in growth or weight in Indian children whose diet was supplemented with vitamin A for one year.

Zinc

Zinc deficiency was described nearly three decades ago among the poor of the Middle East (Halstead et al 1972; Prasad et al 1972; Ronaghy et al 1974). Manifestations of the deficiency include severe growth retardation, delayed sexual maturation and an increased incidence of pregnancy complications. Other manifestations include suppressed immunity, poor healing, dermatitis and impairments in neuropsychological functions. Zinc deficiency was found to be associated with diets high in phytate and fibre and low in protein, which were common in much of the Middle East region. Other conditions such as hookworm and schistosomiasis, which lead to blood loss, increase the incidence of zinc deficiency. Geophagia, commonly practised in Iran, was also cited as leading to zinc and iron deficiency (Sandstead 1991).

Animal foods are a significant source of zinc. While cereals can also apparently be good sources, they are high in fibre and phytate, which causes much of the zinc in cereals to be unavailable. For many foods, there is a rough correlation between the zinc content and the protein content. The zinc content of selected foods is shown in Table 18. It is interesting, but not very relevant, that the amount of zinc in oysters is exceptionally high. In addition to the zinc content of foods in the diet, the presence of other dietary components can affect its bioavailability and hence may be involved in the pathogenesis of zinc deficiency. These can be both inhibitors and facilitators. Inhibitors include phytate, oxalate, dietary fibre, products of Maillard browning, phosphopeptide products of the digestion of casein, ferrous iron, calcium, copper and cadmium. Facilitators for zinc absorption include digestible dietary proteins, histidine, cysteine, citrate, picolinate and EDTA (Sandstead et al 1990; Sandstead 1991).

Table 18. Zinc content (mg/100 g of edible portion) and protein content (g/100 g of edible portion) of selected foods.

Food	Zinc	Protein
Oysters	91	7.1
Beef	5.9	25.9
Lamb	4.5	24.5
Chicken	2	27.3
Lentils	3.6	28.1
Milk	0.4	3.3
Rice	1.2	6.6
Wheat flour	2.9	13.7
White flour	0.7	10.3

Source: USDA (1976-1994).

Zinc deficiency can impair growth. Experimentally, zinc supplementation for low-income preschool children in developed countries improved growth (Krebs et al 1984; Gibson et al 1989); breast-fed or low-weight infants showed improved height and weight gain (Walravens et al 1992) on dietary supplementation with zinc. In developing countries, growth-retarded children in Ecuador showed improved height and weight (Dirren et al 1994), and malnourished Jamaican and Chilean children showed improved weight gain when their diets were supplemented with zinc (Golden and Golden 1981; Castillo-Duran et al 1987). Improved linear growth with zinc supplementation has also been demonstrated by Behrens et al (1990) in Bangladeshi children recovering from malnutrition and diarrhoea.

Iodine

Iodine deficiency is also a major public health problem (FAO/WHO 1992), leading to goitre and to impaired physical and mental development. Iodine deficiency in pregnancy can lead to irreversible foetal brain damage as well as stillbirths, spontaneous abortions and congenital abnormalities. Its main cause is an iodine-depleted soil and it can be alleviated by increasing levels of seafood in the diet or by the use of iodine-fortified salt.

Copper

Copper deficiency has been documented in infants recovering from malnutrition as well as in LBW infants and in adults receiving long-term total parenteral nutrition. Copper is found in animal products, whole grains, legumes, nuts and seeds (Johnson and Nielsen 1990). Severe deficiency symptoms include anaemia, inability to produce white blood cells such as the leukocytes and the neutrophils and osteoporosis with increased susceptibility to bone fracture. Mild copper deficiency over a long period may be associated with arthritis, arterial disease, myocardial disease and neurologic effects. Children recovering from severe malnutrition have been shown to have low copper stores and benefit from copper supplementation, especially if they have been fed high-energy, low-copper diets (Castillo-Duran et al 1983). Delayed bone maturation has also been observed in such infants; copper supplementation relieved the condition (Cordano et al 1964). A beneficial effect on weight gain and weight for height was reported by Castillo-Duran and Uauy (1989) when 11 children suffering from malnutrition received a copper supplement of 80 mg/kg per day for one month.

Type I and Type II nutrient deficiencies

A new classification of nutrients based on the response to deficiencies has been proposed by Golden (1995). The first type of response is that of a reduction in the bodily functions involving the deficient nutrient with little effect on growth until the deficiency becomes severe. Such nutrients are referred to as Type I. The second type of response involves early reduction in growth with an avid conservation of the nutrient within the body to make it more internally available and to maintain the cellular concentration of the nutrient. Such nutrients are referred to as Type II. Golden considers that Type I nutrients are required primarily for specific metabolic functions rather than for metabolism in general. They include most of the nutrients that have had traditional deficiency syndromes associated with them, such as iron, iodine, thiamin, folate, vitamin C, and vitamins A, D, E and K. In contrast, Type II nutrients are needed for all cellular functions but deficiencies are not associated with characteristic signs or symptoms. Nevertheless, deficiency is eventually indicated by poor growth, leading to stunting and wasting. These nutrients include protein and specific amino acids, zinc, magnesium, phosphorus, potassium and sodium. The role of food energy is somewhat equivocal. Major differences between Type I and Type II nutrient deficiencies are shown in Table 19.

Type I nutrient deficiencies can be identified by biochemical tests appropriate to the specific pathway or storage site involved, whereas Type II deficiencies can only be identified by growth faltering and anthropometry. In many cases such deficiencies remain unobserved or are associated with environmental factors that also cause growth faltering. Golden (1995) claims that it is important to be aware of these differences and to provide the undernourished not only with Type I but also with Type II nutrients. In many cases, patients are treated with a diet that provides adequate energy and Type I nutrients but without additional Type II nutrients. Deficiency of the latter may have caused stunting and wasting in the first place. Type II nutrient deficiencies may remain uncorrected and the condition is often unalleviated. While there are a number of loose ends in the Golden hypothesis, which is not universally accepted, the concept is useful and may explain some of the causes of growth faltering in children in developing countries. Micronutrient deficiencies such as zinc may be far more widespread than previously supposed.

Table 19. Type I and II nutrient deficiencies.

Source: Golden (1995).

Strategies for intervention

While many people in poorer countries may be meeting their food energy needs, or may have adapted their body size and patterns of activity to the food energy available, their diets may still be lacking in many of the key nutrients needed for growth in children and for the special needs of pregnancy and lactation. The majority of deprived and undernourished people in the world are subsisting on diets heavily based on cereals, which are bulky and are low in high-quality protein and lysine as well as in a number of micronutrients including iron, zinc, vitamin A and copper. Strategies are available for alleviating these deficiencies.

Dietary diversity

The first approach involves improving dietary diversity by stimulating the production and consumption of protein- and micronutrient-rich foods. Foods of animal origin can frequently fulfil this role. Not only are they generally highly desirable but they can provide good quantities of the nutrients likely to be low or non-existent in cereal-based diets. The addition of even small amounts of animal foods to the diet can improve dietary quality significantly, information that nutrition education programmes should make more widely known.

Animal foods have been considered above as a group with similar nutritional composition. While this is true for their content of lysine when expressed as milligrams of lysine per gram of protein, it is far from true for other micronutrients. Table 20 shows how far white wheat flour, lean lamb meat, whole milk and chicken eggs meet the needs of a young child for food energy, protein, lysine and a number of micronutrients. One hundred kilocalories of all four foods supply about 8% of the daily food energy needs (1300 kcal/day) of a child aged 1 to 3. Lean meat, providing the same amount of energy, provides almost 100% of protein needs and exceeds lysine requirements. White flour provides negligible amounts of lysine. The 100 kcal of whole milk contains more fat than the lean meat and provides calcium and riboflavin, but is a poorer source of protein and lysine than the meat. Milk, however, is not a good source of zinc or iron while lean meat provides these as well as riboflavin. Eggs are a good source of protein, lysine and riboflavin. The degree to which nutritional needs are met would, of course, differ significantly if whole-wheat flour, fatty meat and skim milk were used instead. The diet should, whenever possible, include a variety of animal foods.

Food fortification

A complementary approach is food fortification by adding micronutrients to common foods. This fortification is especially applicable to cereals when used in a milled form. Fortification is more difficult where there are many small-scale producers, but it can be very effective where large, centralised milling facilities exist. Staple foods can also be enriched through plant breeding (Bouis 1995). This technique may become a major strategy in the future.

Table 20. Percentage of young child’s (1-3 years) nutrient requirement provided by 100 kcal of flour, meat, milk or egg.

Food	Fresh weight (g)	Total energy (%)	Total protein (%)	Total lysine (%)	Calcium (%)	Ribo-flavin (%)	Zinc (%)	Iron (%)
Flour1	28	8	21	7	0.5	1	2>	3
Meat2	74	8	95	144	1	22	31	13
Milk3	164	8	34	46	24	33	6	0.8
Egg4	67	8	52	65	4	43	7	10

1. White, unenriched wheat flour.
2. Lean lamb meat.
3. Whole cow milk.
4. Whole chicken egg without shell.
Source: Nutrient composition, USDA (1976-1994); child requirement, NAS-NRC (1989).

Supplementation

Supplementation is the direct individual supply of the nutrient, orally or by other means, such as injection. This option is generally applicable only as a temporary measure until long-term dietary solutions can be implemented, usually because of economic improvements. Supplementation, nevertheless, has been and remains very successful in alleviating the problems of iron-deficiency anaemia and vitamin A deficiency.

Public health measures

Additional strategies require public health measures and legislation to address critical environmental factors such as water quality, sanitation and food hygiene, and to promote essential services such as immunisation programmes, control of endemic diseases, maternal and child health, primary health care and health education and information (FAO/WHO 1992). The UNICEF/WHO Child Survival Strategy, which includes growth monitoring, oral rehydration, breast feeding and immunisation, is used widely and has been a major factor in reducing infant and child mortality rates world-wide.

Summary and conclusions

Malnutrition, in both its acute and chronic forms, and most micronutrient deficiencies mainly affect poor people who have no access to adequate food, clean water, basic services or appropriate education and information (FAO/WHO 1992). The consequences of malnutrition are varied and far reaching. In infants and young children, undernutrition and growth retardation are associated with reduced physical activity, lowered resistance to infection, impaired intellectual development and increased morbidity and mortality. Low birth weight, itself commonly a result of maternal malnutrition, is associated with impairment of subsequent growth and high neonatal and infant mortality.

In women, poor nutritional status is linked with an increased prevalence of anaemia, problems during pregnancy and childbirth, poor intra-uterine growth, low birth weight and perinatal mortality. In adults, undernourishment and anaemia can lead to poor health and productivity, resulting in impaired physical and intellectual performance, which can also constrain community and national development.

Nutritional care is also of supreme importance. This care includes the role of women and their ability to allocate time to child care and breast feeding. Factors that affect the role of women include male and female participation in economic activities, family size, time spent on food preparation, per capita expenditure on food, parental education, the number of children under six years, and the age and sex of the child (Chaudhury 1984; 1985; 1986).

All the above factors are important in determining nutritional status as they affect the availability of different foods. Consumption of expensive animal foods is excessive in developed countries and low in developing ones. Animal foods contain good-quality protein, essential amino acids such as lysine, and micronutrients such as iron, zinc, copper and vitamin A in highly bioavailable forms. The provision of small quantities of these foods can significantly improve diets in the developing world.

Until relatively recently, only the immediate causes of malnutrition were discussed, mainly related to deficiencies of food and nutrients. The underlying and basic causes, which were considered as being outside the concern of nutritionists, are now, however, more widely accepted. It is now recognised that, no matter how desirable the role of animal foods in improving nutritional status, greater consumption will not occur in poor countries unless either purchasing power increases or production costs are reduced. The crux of the problem is poverty, which is and will remain for the foreseeable future the root cause of malnutrition. The political will must be found in all societies to give a much greater priority in global development to the alleviation of poverty.

References

Allen L.H. 1994. Nutritional influences on linear growth: a general review. European Journal of Clinical Nutrition 48 (1):75S-89S.

Aukett M.A., Parks Y.A., Scott P.H. and Wharton B.A. 1986. Treatment with iron increases weight gain and psychomotor development. Archives of the Diseases of Childhood 61:849-857.

Behrens R.H., Tomkins A.M. and Roy S.K. 1990. Zinc supplementation against diarrhoea: a fortification against malnutrition? Lancet: 442-443.

Bouis H. 1995. Enrichment of food staples through plant breeding: a new strategy for fighting micronutrient malnutrition. Administrative Committee on Coordination—Subcommittee on Nutrition of the United Nations. ACC/SCN c/o WHO, Geneva, Switzerland. SCN News 12:15-19.

Briggs G.M. and Schweigert B.S. 1990. An overview of meat in the diet. In: Pearson A.M. and Dutson T.R. (eds), Meat and Health: Advances in Meat Research, vol. 6. Elsevier Applied Science, London and New York. pp. 1-18.

Brink E.W., Perera W.D.A. and Broske S.P. 1979. Vitamin A status of children in Sri Lanka. American Journal of Clinical Nutrition 32:84-91.

Castillo-Duran C. and Uauy R. 1989. Copper deficiency impairs growth of infants recovering from malnutrition. American Journal of Clinical Nutrition 47:710-714.

Castillo-Duran C., Fisberg M., Egana J.I., Valenzuela A. and Uauy R. 1983. Controlled trial of copper supplementation during the recovery from marasmus. American Journal of Clinical Nutrition 37:898-903.

Castillo-Duran C., Heresi G., Fisberg M. and Uauy R. 1987. Controlled trial of zinc supplementation during recovery from malnutrition effects on growth and immune function. American Journal of Clinical Nutrition 45:602-608.

Chaudhury R.H. 1984. Determinants of dietary intake and dietary adequacy for pre-school children in Bangladesh. Food and Nutrition Bulletin 6(4):24-33.

Chaudhury R.H. 1985. Determinants of nutrient adequacy for lactating and pregnant mothers in a rural area in Bangladesh. Food and Nutrition Bulletin 7(1):26-32.

Chaudhury R.H. 1986. Determinants of nutrient adequacy in a rural area in Bangladesh. Food and Nutrition Bulletin 8(4):24-31.

Chwang L.C., Soemantri A.G. and Pollitt E. 1988. Iron supplementation and physical growth of rural Indonesian children. American Journal of Clinical Nutrition 47:496-1001.

Cordano A., Baertl J.M. and Graham G.G. 1964. Copper deficiency in infancy. Pediatrics 34:324-325.

Dirren H., Barclay D., Gil Ramos J., Montalvo M.M. and Lozano R. 1994. Zinc supplementation and infant growth in Ecuador. In: Allen L.H., King J.C. and Lonnerdal B. (eds), Nutrient Regulation during Pregnancy, Lactation and Infant Growth. Advances in Experimental Medicine and Biology. Plenum Press, New York. pp. 215-222.

FAO (Food and Agriculture Organization of the United Nations). 1994. Body Mass Index: A Measure of Chronic Energy Deficiency in Adults. FAO Food and Nutrition Paper No. 56. Main authors, P.S. Shetty and W.P.T. James. FAO, Rome.

FAO (Food and Agriculture Organization of the United Nations). 1996a. The Sixth World Food Survey. FAO, Rome. 154 pp.

FAO (Food and Agriculture Organization of the United Nations). 1996b. World Food Summit. Technical background documents 1-5, vol. 1. FAO, Rome. 45 pp.

FAO/WHO (Food and Agriculture Organization of the United Nations/World Health Organization of the United Nations). 1991. Report of the Joint FAO/WHO Expert Consultation on Protein Quality Evaluation, Bethesda, Maryland. FAO Food and Nutrition Paper No. 51. FAO, Rome, Italy.

FAO/WHO (Food and Agricultural Organization of the United Nations/World Health Organization). 1992. International Conference on Nutrition: Nutrition and Development—A Global Assessment. FAO, Rome, Italy.

FAO/WHO/UNU (Food and Agricultural Organization of the United Nations/World Health Organization/United Nations University). 1985. Energy and Protein Requirements. Report of a Joint FAO/WHO/UNU Expert Consultation. Technical Report Series No. 724. FAO, (Food and Agriculture Organization of the United Nations), Rome. 207 pp.

FAOSTAT. 1996. Food Balance Sheets 1961-1994. FAOSTAT-PC: FAO Computerized Information Series, version 3. FAO (Food and Agricultural Organizaion of the United Nations) , Rome.

Gibson R.S., Smit Vanderkooy P.D., MacDonald A.C., Goldman A., Ryan B.A. and Berry M. 1989. A growth limiting mild zinc deficiency syndrome in some southern Ontario boys with low height percentiles. American Journal of Clinical Nutrition 49:1266-1273.

Golden M. 1995. Specific deficiencies versus growth failure: Type I and Type II nutrients. Administrative Committee on Coordination—Subcommittee on Nutrition of the United Nations. ACC/SCN c/o WHO, Geneva, Switzerland. SCN News 12:10-14.

Golden M.H.N. and Golden B.E. 1981. Effect of zinc supplementation on dietary intake, rate of weight gain and energy cost of tissue deposition in children recovering from severe malnutrition. American Journal of Clinical Nutrition 34:900-908.

Halstead J.A., Ronaghy H.A., Abadi P. et al. 1972. Zinc deficiency in man. American Journal of Medicine 53:277-284.

Heymsfield, S.B. and Williams P.J. 1988. Nutritional assessment by clinical and biochemical methods. In: Shils M.E. and Young V.R. (eds), Modern Nutrition in Health and Disease, 7th ed. Lea and Febiger, Philadelphia. pp. 817-860.

IDECG (International Dietary Energy Consultative Group). 1996. Energy and protein requirements. In: Scrimshaw N.S., Waterlow J.C. and Schorch B. European Journal of Clinical Nutrition, vol. 100 suppl. 1.

James, W.P.T. 1994. The challenge of adult chronic energy deficiency. In: James W.P.T. and Ralph A. (eds), The Functional Significance of Low Body Mass Index. European Journal of Clinical Nutrition 48 (3):51-59.

Johnson P.E. and Nielsen F.H. 1990. Copper, manganese, cobalt and magnesium. In: Pearson A.M. and Dutson T.R. (eds), Meat and Health: Advances in Meat Research, vol. 6. pp 275-300.

Jonnson, U. 1995. Towards an improved strategy for nutrition surveillance. Food and Nutrition Bulletin 16(2):102-111.

Krebs N.F., Hambidge K.M. and Walravens P.A. 1984. Increased food intake of young children receiving a zinc supplement. American Journal of Diseases of Childhood 138:270-273.

Latham M.C., Stephenson L.S., Kinoti S.N., Zaman M.S. and Kurz K.M. 1990. Improvements in growth following iron supplementation in young Kenyan children. Nutrition 6:159-165.

Lusk, G. 1928. The Elements of the Science of Nutrition, 4th ed. W.B. Saunders, Philadelphia and London.

Mele L., West K.P., Kusdiono P.A., Nendrawati H., Tilden R.L. and Tarwotjo I. 1991. Nutritional and household risk factors for xerophthalmia in Aceh, Indonesia: a case control study. American Journal of Clinical Nutrition 53:1460-1465.

Monsen E.R., Halberg L., Layrisse M., Hegsted D.M., Cook J.D., Mertz W. and Finch C.A. 1978. Estimation of available dietary iron. American Journal of Clinical Nutrition 31:134-141.

Muhilal P.D., Idjradinata Y.R., Muherdiyantiningsih and Karyadi D. 1988. Vitamin A fortified monosodium glutamate and health, growth and survival of children: a controlled field trial. American Journal of Clinical Nutrition 48:1271-1276.

NAS-NRC (National Academy of Sciences-National Research Council). 1953. Recommended Dietary Allowances. Publication 302. National Academy of Sciences, Washington, D.C.

NAS-NRC (National Academy of Sciences-National Research Council). 1989. Recommended Dietary Allowances, 10th rev. ed. National Academy of Sciences, Washington, D.C.

Pellett P.L. 1990. Protein requirements in humans. American Journal Clinical Nutrition 51:723-737.

Pellett P.L. 1996. World essential amino acid supply with special attention to South-East Asia. Food Nutrition Bulletin. 17(3):204-234.

Pellett P.L. and Young V.R. 1988. The contribution of livestock products to human dietary needs with special reference to West Asia and North Africa. In: Thomson E.F. and Thomson F.S. (eds), Increasing Small Ruminant Productivity in Semi-Arid Areas. Kluwer Academic Publishers, Dortrecht, The Netherlands, for ICARDA, Aleppo, Syria.

Pellett P.L. and Young V.R. 1990. The role of meat as a source of protein and essential amino acids in human protein nutrition. In: Pearson A.M. and Dutson T.R. (eds), Meat and Health: Advances in Meat Research, vol. 6. Elsevier Applied Science, London and New York.

Prasad A.S., Halstead J.A. and Nadimi M. 1972. Syndrome of iron deficiency anemia, hepatosplenomegaly, hypogonadism, dwarfism and geophagia. American Journal of Medicine 31:532-546.

Rahmathulla L., Underwood B.A., Thulasiraj R.D. and Milton R.C. 1991. Diarrhea, respiratory infections and growth are not affected by a weekly low dose of vitamin A supplement: a masked controlled field trial in children in southern India. American Journal of Clinical Nutrition 54:568-577.

Ronaghy H.S., Reinhold J.G., Mahloudji M. et al. 1974. Zinc supplementation of malnourished boys in Iran: increased growth and other effects. American Journal of Clinical Nutrition 27:112-121.

Sandstead H.H. 1991. Zinc deficiency: a public health problem? American Journal of Diseases of Childhood 145(8):853-859.

Sandstead H.H. Darnell L.S. and Wallwork J.C. 1990. Role of zinc and the contribution of meat to human nutrition. In: Pearson A.M. and Dutson T.R. (eds), Meat and Health: Advances in Meat Research, vol. 6. Elsevier Applied Science, London and New York. pp 237-274.

Scrimshaw, N.S., Taylor, C.E. and Gordon, J.E. 1968. Interactions of Nutrition and Infection. WHO Monograph Series No. 57. World Health Organization, Geneva.

UNDP (United Nations Development Programme). 1996. Human Development Report. Published for UNDP by Oxford University Press, New York and Oxford. 229 pp.

UNICEF(United Nations International Children’s Emergency Fund). 1990. Strategy for Improved Nutrition of Children and Women in Developing Countries. UNICEF, New York.

UNICEF (United Nations International Children’s Emergency Fund). 1996. The State of the World’s Children. Oxford University Press, New York and Oxford. 103 pp.

UNICEF (United Nations International Children’s Emergency Fund). 1997. The State of the World’s Children. Oxford University Press, New York and Oxford.

USAID (United States Agency for International Development). 1978. Arab Republic of Egypt: National Nutrition Survey. USAID, Department of State, Washington, DC.

USDA (United States Department of Agriculture). 1976-1994. Agricultural Handbook No. 8-1(1976); 8-2(1977); 8-5(1979); 8-6(1980); 8-7(1982); 8-8(1982); 8-9(1982); 8-10(1983); 8-11(1984); 8-12(1986); 8-13(1986); 8-14(1986); 8-15(1987); 8-16(1986); 8-17(1989); 8-18(1994); 8-19(1991); 8-20(1989); 8-21(1988). Agriculture Research Service, United States Department of Agriculture, Washington, D.C.

Walravens P.A., Chakar A., Mokni R., Denise J. and Lemonnier D. 1992. Zinc supplements in breast fed infants. Lancet 3100:683-685.

WHO (World Health Organization). 1986. WHO Working Group on the Use and Interpretation of Anthropometric Indicators of Nutritional Status. Bulletin of the World Health Organization 64:929-941.

WHO (World Health Organization). 1995. Physical Status: The Use and Interpretation of Anthropometry. Report of a WHO Expert Committee. WHO Technical Report Series No. 854. World Health Organization, Geneva. 452 pp.

WHO-UNU-UNICEF (World Health Organization-United Nations University-United Nation’s Children’s Emergency Fund). 1993. Population Studies of the Relative Effectiveness of Weekly and Daily Iron Supplementation in Pregnant Women, Adolescent Girls and Preschool Children. Master Protocol. WHO, Geneva.

Young V.R. and Pellett P.L. 1990. Current concepts concerning indispensable amino acid needs in adults and the implications for international nutrition planning. Food and Nutrition Bulletin 12(4):289-299.

Young V.R. and Pellett P.L. 1994. Plant proteins in relation to human protein and amino acid nutrition. American Journal of Clinical Nutrition 59 (5S):1203S-1212S. May suppl.

Young V.R., Bier D.M. and Pellett P.L. 1989. A theoretical basis for increasing current estimates of the amino acid requirements in adult man with experimental support. American Journal of Clinical Nutrition 100(1):80-92.