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World essential amino acid supply with special attention to South-East Asia

Peter L. Pellett

Abstract

On the basis of calculations using regional and country food balance sheets, dietary surveys from Pakistan and India, and amino acid composition data, it is proposed that the essential amino acid lysine may be relatively lacking in many areas of the world where diets heavily based on cereals are consumed. By combining food balance sheet and gross national product data, it can be demonstrated that as wealth increases, not only are more food energy and protein available, but there are also major changes in the pattern of foods selected. When dietary and health data are stratified by gross national product, the poorest countries, with a combined population of nearly 3,000 million, have the highest proportion of their protein originating from plant sources. These are also the countries with the lowest life expectancy and the highest mortality rate among children under five years of age. Rich countries, in contrast, obtain much of their protein from animal sources. Such different dietary patterns of the rich and the poor lead to very different daily availabilities of lysine Although large differences also exist for all other essential amino acids, the difference is considered to be nutritionally significant only for lysine The coefficient of variation (CV %) in lysine content in some 100 dietary calculations was more than three times the average CV % of the other essential amino acids. The amino acid compositions of animal, pulse, and cereal proteins are also sufficiently different from each other to allow food group data to be used to predict the lysine value of diets. Dietary survey data from both India and Pakistan showed wide intra-country variations of lysine availability. Average lysine values were low in both countries and would indicate a considerable risk of inadequate levels of intake in many subsections of the population. Strategies to alleviate possible global problems of low lysine supply must include improving dietary diversity as well as consideration of cereal nutrient fortification.

Introduction

Global nutrition priorities

Despite major improvements in health and social services in recent years, as well as in food availability (table 1), hunger and malnutrition remain devastating problems facing the majority of the world's poor. One out of five persons in the developing world is chronically undernourished, nearly 200 million children suffer from protein-energy malnutrition, and over 2,000 million experience micronutrient deficiencies. In addition, diet-related non-communicable diseases, such as obesity, cardiovascular diseases, diabetes, and some forms of cancer, exist or are emerging as public health problems in many countries [1].

TABLE 1. Per capita dietary energy supply by region or economic group (kcal/person/day)

Source: ref. 1.
a. Includes the least developed countries.

The improvements have, however, been considerable. An estimated 941 million people were chronically undernourished in 1969 1971, compared with some 786 million in 1988-1990 (table 2). Dietary energy supplies in developing countries also continued to increase in the 1980s, although at a slower rate than in the previous decade (table 1). Protein-energy malnutrition, however, as assessed by physical growth and body measurements, is still widespread throughout the world, primarily among those under five years of age.

TABLE 2 Estimate of chronic undernutrition^a in developing regions for 1969-71, 1979--81, and 1988-90

Source: ref. 1.
a. Defined as "chronic dietary energy deficiency."

Whereas the percentage of underweight children has declined in all continents over the last 15 years, the absolute numbers have remained fairly stable as a result of population increases. The number of underweight children is highest in Asia (155 million), as is shown in table 3. The numbers in Africa, although much smaller, have actually increased. Mortality rates are correlated with underweight status and may be as high as 200 deaths per 1,000 live births in the least developed countries, compared with an average rate of 20 per 1,000 for the developed parts of the world. The prevalence of low-birthweight (<2.5 kg) infants in 1991 was nearly 19% in developing countries, with very high rates in South-East Asia and Africa, compared with 6% in developed countries. Low birthweight is an indicator of foetal undernutrition resulting from maternal undernutrition or infections.

TABLE 3. Prevalence and number of underweight^a children under five years of age by region

Source: ref. 1.

1. Underweight is defined as weight-for-age less than minus 2 SD of the WHO reference.
2. Population projections for 1990 and 2005 are based on the medium variant from the UN.
3. East, middle, southern, and western Africa, and including the Sudan from North Africa.
4. Excluding the countries of the former USSR, and the Near East (or western Asia), which are tabluated separately.
5. Papua New Guinea and Vanuatu.
6. Excluding Gaza Strip and Cyprus.

Micronutrient deficiencies

The most prevalent micronutrient deficiencies are lack of iron (over 2,000 million affected), lack of iodine (over 1,000 million at risk), and insufficient vitamin A (40 million affected). Iron deficiency primarily affects pregnant women, women of childbearing age, and young children, and can affect half the people in these segments of the population. Various other micronutrient deficiencies consisting of a lack of zinc, selenium, and other trace elements affect large numbers of people in various parts of the world [1]. As will be elaborated below, the relative lack of the essential amino acid lysine is also likely to be widespread in vast areas of the world consuming cereal-based diets, including most of South Asia.

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 cognitive abilities, and increased morbidity and mortality.

Low birth-weight, itself commonly a result of maternal malnutrition, is associated with impairment of subsequent growth performance and high neonatal and infant mortality.

In women, poor nutritional status is linked with an increased prevalence of anaemia, pregnancy and delivery problems, and increased rates of intra-uterine growth retardation, 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 constrain community and national development.

Poverty is the root cause of malnutrition. Acute and chronic undernutrition and most micronutrient deficiencies primarily affect poor and deprived people who do not have access to adequate food, live in unsanitary environments without access to clean water and basic services, and lack access to appropriate education and information [1].

Nutrition status is largely influenced by the nutrient content of foods consumed in relation to requirements. Requirements are determined by various factors such as age, sex, body size, physical activity, growth, pregnancy and lactation, infections, and the efficiency of nutrient utilization [2-5]. Adequate water and basic sanitation are thus also essential.

Stable food availability at the national, regional, and household levels is a cornerstone of nutritional well-being. Aggregate estimates of food availability at the global, regional, or country level, while often indicative, cannot truly reflect household or individual food consumption. Food consumption is affected by the ability of households to produce or procure food, which in turn depends on income levels and distribution, food availability and wastage, prices, and consumer choices.

Of supreme importance at the individual level is the role of women and their ability to allocate time to child care. Causative factors here 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 of age, and the children's age and sex [6-8].

World data concerning the numbers of people affected by chronic dietary energy deficiency are presented in table 2. Since these figures do not take into account problems of intra-household food distribution, or seasonal or acute problems of malnutrition or infection, the actual number of undernourished people is likely to be higher. By these estimates, again as with child malnutrition, the largest numbers are in Asia and represent almost 70% of those suffering chronic energy deficiency throughout the world. Energy availability may also affect protein utilization because of the biochemical interrelationships between protein and energy metabolism [9].

Strategies for intervention

The majority of the deprived and undernourished population, especially in South-East Asia, subsists on diets heavily based on cereals. Such diets are likely to be low in a number of micronutrients, including the amino acid lysine. Strategies and activities to alleviate micronutrient deficiencies must include several approaches. The first involves improving dietary diversity by stimulating the production and consumption of micronutrient-rich foods. A complementary approach is fortification of common foods by the addition of micronutrients. Fortification is especially applicable to cereals that are used in a milled form. Fortification can be difficult where there are multiple small-scale producers but can be much simpler where large, centralized milling facilities exist. Additional requirements for successful fortification are the adoption and enforcement of appropriate legislation as well as the convincing of both consumers and professionals that such plans are to their benefit.

Supplementation should only be considered as a temporary measure until long-term solutions can be implemented. It has, nevertheless, been very successful in alleviating the problems of vitamin A deficiency. Additional necessary procedures 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 immunization programmes, control of endemic diseases, maternal and child health, primary health care, and health education and information [1].

Essential amino acid supply

Comparison of data from different countries has shown that as wealth (gross national product) decreases, the availability of food energy decreases and also major changes occur in the pattern of foods that are selected. In particular there are significant decreases in the availability of animal protein foods [10-14]. Further, of the essential amino acids, the difference between the diets of rich and poor people in the amount consumed is greatest for lysine The amino acid compositions of animal, pulse, and cereal proteins are sufficiently distinctive from each other to allow food group data to be used for simple predictions of the lysine value of diets. Standard tables of amino acid composition show that the values for cereals range from 26 to 38 mg lysine/g protein, whereas the values for animal foods range from 70 to 100 mg lysine/g protein [13]. A recent important analysis concerning the world balance of dietary essential amino acids also demonstrated the central role of lysine [15].

Standards of comparison are needed to assess whether a diet meets the needs for essential amino acids, both in absolute quantities, as measured by milligrams of amino acid per day, and qualitative terms, as measured by milligrams of amino acid per gram of protein. Throughout this review the values from FAD/WHO have been used as this standard [5]. For lysine the adult requirement is 58 mg/g protein, which translates to 2,840 mg/day for a young, 65-kg adult male whose protein requirement is 49 g/day. Lower recommendations, based on stable isotope studies, have been published: 50 mg/g protein or 2,450 mg/day for the same young adult male [16].

The human lysine requirement is the subject of current collaborative international research, and future agreement on the actual value is essential for the assessment, on a global basis, of those at risk for deficiency. It is recognized that the use of the FAO/WHO [5] lysine value may result in some over-assessment of those at risk. The requirements for the other essential amino acids are similar in both sets of recommendations. The use of either standard leads to the conclusion that many millions may be at risk for lysine limitation, even if the numbers differ. Risk assessment can, however, be made with accuracy only by using estimates based on individual variability in intake. These data do not exist at present for the populations of South-East Asia. It is recommended that studies be undertaken to estimate individual variability of lysine intake in populations consuming diets based on high levels of cereals.

A further variable mentioned above is the possible interaction between protein and food energy availability [9]. This could affect the protein value of diets when food energy is limiting to a significant degree. Subsequent considerations here make the assumption that food energy availability is not generally in sufficient deficit that protein utilization is severely affected. The following discussion will therefore elaborate and extend observations on foods, diets, amino acid composition, and limiting amino acids in various regions of the world, paying particular attention to the diets of South-East Asia. Nevertheless, the additional effects of food energy deficiency on protein utilization could well be superimposed on the very poorest.

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