Pattern of amino acid requirements in humans: an interspecies comparison using published amino acid requirement recommendations.

We undertook an interspecies comparison of essential (indispensable) amino acid requirements, in relation to those for total protein, to examine whether the current, internationally proposed human amino acid requirement patterns are significantly different from those of other animals. Data were compiled in their original form and then expressed as mg amino acid/g total dietary protein (N X 6.25) required (amino acid requirement pattern). Patterns of requirements within the various species were organized according to four, arbitrary age-developmental groupings (very young, early growth, growth and mature), and these were compared with the requirements for (a) human infants, (b) 2-5 year old children, (c) 10-12 year old children and (c) adults, respectively. Statistical comparisons determined if significant differences existed between humans and other species, at apparently similar age-development stages, for both the total and for individual indispensable amino acids. The sum of the specific indispensable amino acid requirements for humans was significantly different than that for other species at infancy, growth and adulthood; the greatest differences, however, were for the amino acid requirement pattern in adulthood. The change between the very young and adult was the greatest for humans. Some of this difference might be due to experimental factors, including the biological status of a species within the arbitrary groupings described and the criteria used to determine "requirements." Nevertheless, it is difficult to escape the conclusion that the current international human amino acid requirements, for adults in particular, appear to be anomalous when judged against data for other animal species.

Plant proteins in relation to human protein and amino acid nutrition.

Plant protein foods contribute approximately 65% of the per capita supply of protein on a worldwide basis and approximately 32% in the North American region. These sources of protein are discussed in relation to their amino acid content, human amino acid requirements, and dietary protein quality. Mixtures of plant proteins can serve as a complete and well-balanced source of amino acids for meeting human physiological requirements. This short review ends with a list of series of myths and realities concerning the relationship between plant protein and human nutrition and a list of some nutritional issues of concern to the health professional and informed consumer.

Nutritional implications of microparticulated protein.

Recent technological developments have permitted the large-scale preparation of ingredients enriched with microparticulated proteins (MPP) that can be used to replace much or essentially all of the fat in a variety of traditional, full-fat foods. These include ice cream, salad dressings, mayonnaise and cheese spreads. In this paper we consider the nutritional implications of MPP, beginning with an assessment of the need for a fat-substitute and then the potential impact of MPP on the fat content of applicable foods and on the diet as a whole. Under projected conditions of maximum use of these MPP-containing foods by the consumer, the mean reduction in the fat content of the "current U.S. diet" would be about 14%. Although not dramatic, this represents a significant move in the direction of dietary changes that have been recommended by national and international authorities concerned with diet-health relationships. The risk/benefit ratio associated with inclusion of MPP in the diet is considered to be very high. This new development by the food industry is of considerable scientific interest and of potential practical importance for the nutrition and well-being of our society.

Food energy requirements in humans.

The general principles behind the estimation of energy requirements in humans are discussed and a framework is proposed for estimation of energy allowances appropriate to the population of the United States. Although median weights are used for those less than 18 y, lowest mortality values, which approximate the 25th percentile weights for height in the US population, are used as the desirable weights for adults in assessing daily energy needs. For adults the procedure for estimating daily energy allowances involves calculation of resting energy expenditure by use of the Harris-Benedict equation, which is then multiplied by appropriate factors for activity. A factorial approach is followed for the additional needs of pregnancy and lactation. For young children allowances are based on intake data. Tabular data are presented for energy allowances at all ages together with worked examples for a more individualized approach when body size and activity patterns differ significantly from the mean.

A theoretical basis for increasing current estimates of the amino acid requirements in adult man, with experimental support.

Estimates of the minimum (obligatory) rates of loss of indispensable acids via irreversible oxidation in healthy young adults are predicted from published data for obligatory nitrogen losses and from published values for whole-body protein turnover and the efficiency of amino acid recycling. The estimates obtained by these two different approaches are consistent and equal to or in most cases considerably higher than current values for the upper range of the individual amino acid requirements in healthy adults. From these estimates of the obligatory, or minimum, rates of amino acid oxidation, the minimum requirements for indispensable amino acids are predicted. These are about two to three times higher than current requirement figures. Experimental support for these higher requirement figures is presented, based on published 13C-labeled amino acid tracer studies. When these revised estimates are expressed per unit of protein need, the amino acid pattern is similar to the 1985 Food and Agriculture Organization/World Health Organization/United Nations University amino acid scoring pattern for the preschool child (aged 2-5 y).

Protein intake and requirements with reference to diet and health.

We have reviewed, in brief, various aspects of human protein and amino-acid metabolism with particular reference to the assessment of protein and amino acid needs. The current requirements for protein and amino acids in various groups of healthy people were then summarized. Emerging from this discussion was the view that some plant protein foods, such as soy for example, are of much better nutritional value for humans than has been commonly appreciated. The figures for requirements were then compared with intakes characteristic of populations in the developed regions of the world. It is evident that these intakes greatly exceed the minimum physiologic need for most healthy individuals but little is known about the possible health benefit or otherwise of these intake levels of protein. Furthermore, also it was pointed out that consideration of different food proteins in relation to amino acid and nitrogen requirements constitutes an important, but only an initial, basis for evaluating the role of dietary protein and of various food protein sources in human nutrition and health. Different food protein sources influence, in various ways, the utilization of and possibly requirements for other nutrients. This complicates determination of requirements and the setting of rational and safe dietary allowances as well as of dietary guidelines for individuals and population groups. A further assessment of the role and impact of food proteins and their interrelationships with and interactions among other foods and essential nutrients, particularly with respect to the nutritional and metabolic status of free-living individuals and their long-term health, presents a difficult but exciting research challenge to nutrition and other health professionals.

Effect of guar gum, lignin and pectin on proteolytic enzyme levels in the gastrointestinal tract of the rat: a time-based study.

The effects of dietary pectin (P), guar gum (G) and lignin (L) on stomach emptying and potential levels of pepsin, trypsin and chymotrypsin during a 2-h period after force-feeding were investigated in growing rats. All of the fibers delayed stomach emptying by 21-26 min. Total potential pepsin activity over 2 h decreased for P (57%), G (44%) and L (20%). In the intestine, total potential trypsin activity over 2 h increased for L (16%) but decreased for P (21%). Total potential chymotrypsin activity over 2 h increased for L (54%) and G (39%). Sixteen to 21% of the variability in intestinal activity over time was statistically attributable to variation in the weight of intestinal contents. The results indicate that fiber components altered proteolytic enzyme levels in the gastrointestinal tract, but the decreased protein utilization previously observed with these fibers is probably not due to reduced levels of intestinal proteases.

Wheat proteins in relation to protein requirements and availability of amino acids.

Wheat is a major source of plant protein for man. In parallel with other cereal staples, wheat proteins do not contain as high a concentration of the nutritionally indispensable amino acids as do animal protein foods. Thus, when consumed as an essentially sole source of protein they are not utilized with the same efficiency as animal protein foods and more wheat protein is required to meet the physiological needs in children and adults for both total protein and specific indispensable amino acids, especially lysine and also for threonine and tryptophan in specific cases. However, when combined with other food proteins such as legumes, oil seeds or animal products the proteins of wheat exhibit excellent nutritional complementarity. Furthermore, when wheat-based foods are considered in relation to broader concerns for diet, food habits and long-term health it is to be concluded that the proteins of wheat can and should continue to make a nutritionally important role toward meeting the protein and amino acid needs of populations throughout both the developing and developed regions of the world. Further research devoted toward improving the digestibility and overall nutritional value of wheat proteins and developing acceptable and economic sources of wheat protein concentrates should contribute to an even more substantial longterm role of wheat as a source of protein in human nutrition.

Comparison of interlaboratory variation in amino acid analysis and rat growth assays for evaluating protein quality.

Estimates of inter- and intralaboratory variation of protein efficiency ratio (PER), relative PER (RPER), net protein ratio (NPR), relative NPR (RNPR), and nitrogen utilization (NU) were compared with those of amino acid analysis in the same batches of 7 protein sources (ANRC casein, egg white solids, minced beef, soy assay protein, rapeseed protein concentrate, pea flour, and whole wheat flour). Interlaboratory variation (estimated as between-laboratories coefficients of variation, CV) of NPR and RNPR (up to 6.0%) was lower than that of PER (up to 20.2%) and RPER (up to 18.5%). The interlaboratory determination of NPR and RNPR was also more reproducible than that of most essential amino acids (CV up to 10.0%), especially tryptophan (CV up to 23.7%), cystine (CV up to 17.6%), and methionine (CV up to 16.1%). Intralaboratory variation (estimated as within-laboratories CV) of amino acid analysis (up to 4.7%), however, was comparable to that of protein quality indices in most protein sources (up to 6.0%). The significant (P less than 0.01) positive correlations (r = 0.68-0.74) between amino acid scores and protein quality indices based on rat growth were further improved when amino acid scores were corrected for digestibility of protein (r = 0.73-0.78) or individual amino acids (r = 0.79-0.82).

Evaluation of the use of amino acid composition data in assessing the protein quality of meat and poultry products.

A detailed analysis of the amino acid composition data of meat and poultry products, in relation to PER, clearly reveals high correlations between amino acid data expressed in various forms and results of protein quality estimations obtained with the PER assay. The significance of these observations in reference to protein quality evaluation for regulatory purposes will be considered in Background Paper 5.

Amino acid composition in relation to protein nutritional quality of meat and poultry products.

The protein nutritional value of meat, poultry, and their products must be considered in relation to humans. Because direct assessment of protein nutritional value in human subjects is impractical for regulatory purposes, methods based on in vitro (chemical) and animal bioassays for assessment of protein quality have been developed. Herein, a case is made for the use of amino acid data as a basis for regulation of meat and poultry products, where considerations of protein nutritional value are included in the regulation. Current data on the protein nutritional quality of these products are based almost entirely on the use of the rat PER assay procedure, supplemented by data on the amino acid content of these products. Because of the inadequacy of the PER assay, the available data base provides an inadequate body of knowledge from which to draw final recommendations concerning policies for regulation of the protein nutritional quality of meat and poultry products. However, if it is necessary to include a measure of protein nutritional quality in a regulation, these data provide a reasonably sound basis for tentatively recommending use of amino acid composition data rather than the standard rat bioassay procedure. In such an approach based on amino acid composition data, consideration might be given to the contents of hydroxyproline (or possibly proline), 3-methylhistidine, lysine, and nitrogen, with a view to establishing a composite or minimum value for the noncollagen muscle protein content of these products.

Inter- and intra-laboratory variability in rat growth assays for estimating protein quality of foods.

Protein efficiency ratio (PER), relative PER (RPER), net protein ratio (NPR), relative NPR (RNPR), and nitrogen utilization (NU) methods were investigated in an interlaboratory rat growth study. Six collaborating laboratories studied 7 protein sources (ANRC casein; minced beef; soya assay protein, SAP; pea flour; whole wheat flour, WW; rapeseed protein concentrate, RPC; and egg white solids, EW), and their 10 supplementary or complementary mixtures (casein + Met, SAP + Met, pea flour + Met, WW + Lys, WW + casein, WW + beef, WW + SAP, WW + pea flour, WW + RPC, WW + EW). Test protein(s) were added at the 8% level (N X 6.25). Casein + Met was used as the reference protein. Interlaboratory variation (estimated as between-laboratories coefficients of variation) of PER (up to 17.2%) was greater than that of RPER (up to 14.9%), NU (up to 9.5%), NPR (up to 7.0%), and RNPR, which had the lowest variability (up to 4.7%). In most cases, intralaboratory variation (estimated as within-laboratories coefficients of variation) for all the methods was less than 5%.

Effect of dietary fiber components on fecal nitrogen excretion and protein utilization in growing rats.

The effects of purified fiber components and wheat bran on several indices of protein utilization were determined in growing rats. A control diet containing 10% casein was diluted with either cellulose (C), pectin (P), lignin (L), guar gum (G), or wheat bran (W) at fiber levels ranging from 3% to 20%. All fibers except C caused a decrease in net protein ratio (NPR) as compared to the control casein diet. This depression in NPR increased as the dietary fiber level increased. Apparent and true nitrogen digestibilities also decreased with all fibers at all levels. At the highest level of fiber (20%) the depression was greater for G and W and was least for C. NPR when divided by digestibility (analogous to biological value) decreased with P,L, W (all levels) and G (20% level) but not with C. When rats were fed fiber without protein, there was increased excretion of endogenous fecal nitrogen with all fibers at all levels. The results demonstrate that fiber(s) affected protein utilization as measured by NPR, digestibility and endogenous fecal nitrogen excretion and that the negative effect increased with the level of fiber consumed.

Observations on nutritional marasmus in a newly rich nation.

A study was performed in a pediatric hospital in Tripoli, Libya where the familial backgrounds of 50 marasmic infants were compared with those of a group of 50 essentially healthy infants of similar age. Families with marasmic infants had more children but lived in smaller homes than the comparison families. Total income was similar in both sets of families and major consumer items such as television sets, cars, and refrigerators were widely present in both groups. Families with marasmic infants, however, had less literate mothers who tended to breastfeed for shorter periods and to feed purchased pureed baby foods more frequently. The causation of marasmus in these circumstances is probably unhygienic infant feeding despite the availability of clean water and modern kitchen facilities. All 3 factors, adequate housing, adequate income, and an adequately educated mother appear to be necessary simultaneously before infantile marasmus can be prevented.

Diets in the first six months of infants in western Massachusetts. I. Energy-yielding nutrients.

Two hundred sixty-eight infants under six months of age from three ethnic and three income backgrounds were surveyed by trained nutritionists. The cross-sectional findings were based on maternal information on familial and socioeconomic background, prenatal health history, weight and length measurements at birth, health and development of the infant, and finally, a nutritional history and a 24-hr. recall of food intake. Total daily caloric intakes of infants in this group were not significantly different from intakes of the children studied in Denver by the Child Research Council (5). However, the composition of the diets differed. Differences in the carbohydrate, protein, and lipid are due to the use primarily of evaporated milk formulas with gradually decreasing addition of sugar and the high-cholesterol and low-linoleic acid content in the CRC study, and of premodified formulas with constant sugar content and low cholesterol and high linoleic acid in this study.

Diets in the first six months of infants in western Massachusetts. II. Semi-solid foods.

The early introduction of solid foods was observed in three ethnic and income groups in a survey of 268 infants in western Massachusetts. By four weeks of age, cereal had been introduced into the diets of 57 per cent and fruit to 32 per cent of the infants. Patterns of introducing and feeding solid foods to breast-and formula-fed infants were similar and were related more to income than to type of milk fed. The cost of infant feeding can draw heavily on the family's food budget.