Revisiting PINI Scoring in Light of Recent Biological Advances

The prognostic inflammatory and nutritional index (PINI) is a simple scoring formula allowing the follow-up of dietary protein restriction and infectious complications affecting critically ill patients hospitalized in medical and surgical wards. The World Health organization (WHO) has recently recommended using the binary CRP (C-reactive protein) and AGP (α1-acid glycoprotein) numerators of the PINI formula in underprivileged inhabitants of developing countries to evaluate their (sub)clinical infectious states making their chronic malnutrition worse. These studies, mainly located in Africa and Asia, demonstrate that children and women enduring the combined effects of infectious burden and (micro)nutrient deprivation (principally retinol and iron) usually manifest persistent refractoriness and slackened recovery throughout dietary rehabilitation. The additive measurement of ALB (albumin) and TTR (transthyretin) composing the denominator of the PINI formula is shown to be helpful in grading the downsizing of lean body mass (LBM), a cornerstone of bodybuilding. The confrontation of these four objective parameters thus allows the quantification of the respective importance of nutritional and inflammatory components of any disease process, taking into account that TTR is the sole plasma protein remaining highly correlated to the fluctuations of LBM. The below review highlights the prevailing roles played by protein nutritional states in the release of plasma retinol to target tissues and to the restoration of iron-deficient anemias.

Human Amino Acid Requirements: A Re-Evaluation

The most recent internationally stated estimates of the amino acid requirements in adult humans are those given in the 1985 report of the Joint FAO/WHO/UNU Expert Consultation on Energy and Protein Requirements. In this review we present, in brief a number of scientific concerns and problems that lead us to conclude that these current recommendations for amino acid requirements are not valid and that the appropriate values are likely to be considerably higher. Following a short review of the C-labelled amino acid tracer studies carried out at the Massachusetts of Technology (MIT) and designed to reassess the requirements for specific indispensable amino acids, we focus particular attention on the lysine requirement in adults. When various criteria and methods are used to estimate this requirement, it appears that a cohesive body of data indicates the mean requirement value for lysine in healthy adults to be about 30 mg/kg/day or 50 mg/g protein. Although this value contrasts with the FAO/WHO/UNU value of 12 mg/kg/day or 16 ma/g protein, this new, tentative requirement value is consistent with findings from studies carried out earlier at MIT on the nutritional quality of wheat proteins. We propose that it would be prudent to apply the MIT amino acid requirement pattern (see Food and Nutrition Bulletin 1990;12:298–300), rather than the 1985 FAO/WHO/UNU adult amino acid requirement pattern, in the design and implementation of sound nutrition policies and programmes that include considerations of the amount and quality of the protein component of national and regional diets.

World Essential Amino Acid Supply with Special Attention to South-East Asia

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.

World Balance of Dietary Essential Amino Acids Relative to the 1989 Fao/Who Protein Scoring Pattern

The world imbalance of dietary essential amino acids was studied using the latest available protein-supply data (1987–89) and the revised 1989 FAO/WHO protein scoring pattern in comparison with the 1973 FAO/WHO pattern, the 1985 FAO/WHO/UNU pattern, and a pattern proposed by Young et al. in 1989. The results obtained using the 1989 FAO/WHO scoring pattern indicate that the first limiting amino acid for developed countries is usually tryptophan, and that for developing countries is mainly lysine. Similar findings resulted with the Young pattern, but results using the 1973 and 1985 patterns differed substantially. On the basis of the 1989 FAO/WHO pattern, lysine was found to be the first limiting amino acid in the dietary protein supplies of 121 of the 164 countries studied worldwide; it is estimated that the total lysine deficiency in these 121 countries, the amount that would be needed to bring it to the level of the second limiting amino acid, was 1.15 million metric tons per year for 1987–89. In addition, same global correlations of protein and amino acid supplies with gross domestic product were recalculated in US dollars at 1985 prices.

Effect of lysine supplementation on hypertensive men and women in selected peri-urban community in Ghana

Background

Lysine is one of the essential amino acids and in cereal based diets it is known to be the most limiting and therefore determines the quality of dietary protein in such diets. This study investigated the effect of lysine supplementation on blood pressure of hypertensive adults in selected peri-urban community in Accra, Ghana.

Methods

The study was a randomized double-blind controlled study made up of adults men and women assigned to a lysine supplemented group and a placebo-supplemented (control) group. The subjects aged between 18 – 45 years and totaling 180.

Results

Total of 50 (28%) of the participating were hypertensive defined as Systolic Blood Pressure (SBP) ≥140 mmHg. The mean SBP of lysine-supplemented group significantly dropped from 146.11 ± 11.92 to 128.95 ± 10.44 mmHg (p = 0.02). That of women also dropped from 144.12 ± 10.41 to 132.28 ± 10.69 mmHg, (p = 0.06 while the control group had there SBP remained fairly constant after 112 days of intervention with changes in men from 145.79 ± 12.56 to 142.79 ± 11.07 mmHg (p = 0.32) and women in the control had very little drop from 145.15 ± 14.79 to 145.00 ± 17.93 mmHg (p = 0.96).

Conclusion

Lysine supplementation resulted in normalization/reduction of blood pressure of hypertensive subjects who have suboptimal lysine intake.

Current and Forward-Looking Approaches to Technological and Nutritional Improvements of Gluten-Free Bread with Legume Flours: A Critical Review

The gluten-free market currently offers a range of products which can be safely consumed by patients affected by celiac disease. Nevertheless, challenges for optimal formulation remain on the way in terms of appreciable texture, flavor, and adequate nutritional characteristics. Within that framework, legumes have recently attracted attention among scientists as structure- and texture-forming agents, as source of nutrients and bioactive compounds, and as a low-glycemic-index ingredient. This work aims at providing an updated and comprehensive overview of the advantages and disadvantages in the use of legumes in gluten-free breadmaking. It also shows how legumes can contribute to tackling the main technological, nutritional, and organoleptic challenges. From this critical analysis, it emerged that viscoelastic properties of gluten-free bread batter can be enhanced by the use of carob germ, chickpea, lupin, and soybean. Gluten-free bread organoleptic acceptability can be improved by incorporating leguminous flours, such as carob, chickpea, lupin, and soybean. Moreover, a better nutritional quality of gluten-free bread can be obtained by the addition of chickpea and soybean. Gaps and needs in the use of legumes in gluten-free breadmaking emerged and were gathered together to have a sound basis for future studies. The technological and nutritional potential of sourdough should be more extensively exploited. Moreover, in vitro and in vivo studies should be prompted to understand the health benefits of bread formulated with legumes. A holistic approach, interfacing food science, nutrition, and health might help to have, on the market, products with improved sensory properties and nutritional profile.

Lysine requirements of moderately undernourished school-aged Indian children are reduced by treatment for intestinal parasites as measured by the indicator amino acid oxidation technique

BACKGROUND

Lysine requirements of well-nourished children from developing regions have been found to be similar to those of children from developed regions (33.5 mg · kg⁻¹ · d⁻¹). However, intestinal parasites have been shown to increase lysine requirements in undernourished adults, and it is not known if a similar phenomenon occurs in undernourished children from poor and unsanitary environments.

OBJECTIVE

Our objective was to measure the lysine requirement of moderately undernourished school-aged Indian children by the indicator amino acid oxidation technique before and after successful treatment for intestinal parasites.

METHODS

Twenty-one undernourished school-aged children (∼8 y of age) with z scores between -2 SD and -3 SD for height-for-age or weight-for-age, who tested positive for intestinal parasites, were studied before and after successful antiparasite treatment. Children were fed any 2 of 7 levels of lysine intakes (5, 15, 25, 35, 50, 65, and 80 mg · kg⁻¹ · d⁻¹) in random order. The lysine requirement was determined by applying a 2-phase linear regression crossover analysis on the fractional oxidation rate of the tracer L-[1-¹³C] phenylalanine in response to the graded lysine intakes.

RESULTS

The lysine requirement of undernourished children with intestinal parasite infestations was determined to be 42.8 mg · kg⁻¹ · d⁻¹ (95% CI: 32.6, 53.1 mg · kg⁻¹ · d⁻¹), and after successful antiparasitic treatment it was determined to be 35.5 mg · kg⁻¹ · d⁻¹ (95% CI: 25.5, 45.5 mg · kg⁻¹ · d⁻¹). The results were significantly different (P < 0.05), although the 95% CIs overlapped.

CONCLUSIONS

The lysine requirement in undernourished children is similar to that of well-nourished children, and intestinal parasitic infestation increased the lysine requirement by ∼20%.

Nutritional essentiality of sulfur in health and disease

Sulfur is the seventh most abundant element measurable in the human body and is supplied mainly by the intake of methionine (Met), an indispensable amino acid found in plant and animal proteins. Met controls the initiation of protein synthesis, governs major metabolic and catalytic activities, and may undergo reversible redox processes safeguarding protein integrity. Withdrawal of Met from customary diets causes the greatest downsizing of lean body mass following either unachieved replenishment (malnutrition) or excessive losses (inflammation). These physiopathologically unrelated morbidities nevertheless stimulate comparable remethylation reactions from homocysteine, indicating that Met homeostasis benefits from high metabolic priority. Inhibition of cystathionine-β-synthase activity causes the upstream sequestration of homocysteine and the downstream drop in cysteine and glutathione. Consequently, the enzymatic production of hydrogen sulfide and the nonenzymatic reduction of elemental sulfur to hydrogen sulfide are impaired. Sulfur operates as cofactor of several enzymes critically involved in the regulation of oxidative processes. A combination of malnutrition and nutritional deprivation of sulfur maximizes the risk of cardiovascular disorders and stroke, constituting a novel clinical entity that threatens plant-eating population groups.

vProtein: identifying optimal amino acid complements from plant-based foods

BACKGROUND

Indispensible amino acids (IAAs) are used by the body in different proportions. Most animal-based foods provide these IAAs in roughly the needed proportions, but many plant-based foods provide different proportions of IAAs. To explore how these plant-based foods can be better used in human nutrition, we have created the computational tool vProtein to identify optimal food complements to satisfy human protein needs.

METHODS

vProtein uses 1251 plant-based foods listed in the United States Department of Agriculture standard release 22 database to determine the quantity of each food or pair of foods required to satisfy human IAA needs as determined by the 2005 daily recommended intake. The quantity of food in a pair is found using a linear programming approach that minimizes total calories, total excess IAAs, or the total weight of the combination.

RESULTS

For single foods, vProtein identifies foods with particularly balanced IAA patterns such as wheat germ, quinoa, and cauliflower. vProtein also identifies foods with particularly unbalanced IAA patterns such as macadamia nuts, degermed corn products, and wakame seaweed. Although less useful alone, some unbalanced foods provide unusually good complements, such as Brazil nuts to legumes. Interestingly, vProtein finds no statistically significant bias toward grain/legume pairings for protein complementation. These analyses suggest that pairings of plant-based foods should be based on the individual foods themselves instead of based on broader food group-food group pairings. Overall, the most efficient pairings include sweet corn/tomatoes, apple/coconut, and sweet corn/cherry. The top pairings also highlight the utility of less common protein sources such as the seaweeds laver and spirulina, pumpkin leaves, and lambsquarters. From a public health perspective, many of the food pairings represent novel, low cost food sources to combat malnutrition. Full analysis results are available online at http://www.foodwiki.com/vprotein.

Alpha-aminoadipate delta-semialdehyde synthase mRNA knockdown reduces the lysine requirement of a mouse hepatic cell line

Alpha-aminoadipate delta-semialdehyde synthase (AASS) is the bifunctional enzyme containing the lysine alpha-ketoglutarate reductase (LKR) and saccharopine dehydrogenase activities responsible for the first 2 steps in the irreversible catabolism of lysine. A rare disease in humans, familial hyperlysinemia, can be caused by very low LKR activity and, as expected, reduces the lysine "requirement" of the individual. This concept was applied to a murine hepatic cell line (ATCC, FL83B) utilizing RNA interference (RNAi) to achieve AASS mRNA knockdown. Cells were antibiotic selected for stable transfection of 2 plasmids that express different short hairpin RNA sequences for AASS knockdown. Compared with the wild-type cell line, AASS mRNA abundance was reduced 79.0 +/- 6.4% (P < 0.05), resulting in a 29.8 +/- 5.2% (P < 0.05) reduction in AASS protein abundance, 41.3 +/- 10.0% (P < 0.05) less LKR activity, and a reduction in lysine oxidation by 50.7 +/- 11.8%. To determine the effect of AASS knockdown on the lysine requirement, cells were grown in media containing 12.5, 25.0, 50.0, 100, or 200 micromol/L lysine. Using a segmented model approach for growth rate analysis, the lysine requirement of the cell line with AASS silencing was 43.4 +/- 1.7 micromol/L, approximately 26% lower (P < 0.05), than the lysine requirement of the wild-type cell line. These results indicate AASS knockdown decreases the lysine requirement of the cell via a reduction of lysine catabolism through the saccharopine pathway, providing the initial proof in principle that RNAi can be used to reduce the nutrient requirement of a system.

Fifty-Five-Year Personal Experience with Human Nutrition Worldwide

By 1950 the vitamins had been identified, but little was known of their functions. Beriberi, pellagra, and ariboflavinosis were disappearing, but kwashiorkor and/or marasmus were common in most developing countries. Requirements for protein were still uncertain, and those for essential amino acids or essential fatty acids were unknown. The author's contributions in the field of vitamins began in the 1950s and have been reported in more than 650 publications and in 20 books or monographs. These contributions include establishing the Institute of Nutrition of Central America and Panama, the Department of Nutrition and Food Science at the Massachusetts Institute of Technology, the World Hunger Program of the United Nations University, and the International Nutrition Foundation. His scientific contributions include identification of synergistic interactions of nutrition and infection, use of potassium iodate for fortifying crude moist salt, research in the epidemiology of kwashiorkor and marasmus, development of a successful low-cost protein-rich food for infants and young children, establishment of human protein requirements, and investigation of single-cell protein for food use.

What are the essential elements needed for the determination of amino acid requirements in humans?

The aims of this introductory article are to survey and critically evaluate the concepts and approaches that have been used to assess amino acid adequacy and to hypothesize about possible future directions of research. The issue in question is extensive, consequently this article will be limited to: 1) definitions of amino acid requirements; 2) available techniques to assess amino acid requirements; 3) actual recommendations for healthy adults; 4) factors influencing requirements; and 5) requirements in acute and chronic wasting diseases. Recommendations for amino acid intakes for healthy adults were proposed by the FAO/WHO expert committee in 2001. They have not yet been published. The major factors affecting amino acid requirements are the stage of development, reproductive state, environmental factors, digestibility of dietary proteins, genotype of the individual, and pathological conditions. Remarkably, there are no conclusive data relative to changes in requirements induced by infection, injury, trauma, and renal or liver failure. Future research using modern methods to evaluate requirements must thus receive a high priority. Wasting diseases are associated with deficiencies and imbalances of particular amino acids causing specific changes in requirements. Consequently, a new approach has been used to categorize amino acids as conditionally indispensable according to their functional and physiological properties. Kinetic measurements of plasma amino acids might help to estimate qualitative requirements. Measurement of tissue intracellular free amino acid deficiencies or excesses is another method to estimate qualitative requirements. Based on these measurements tentative values for conditionally indispensable amino acids during disease are given in the article.

Lysine Fortification of Wheat Flour Improves Selected Indices of the Nutritional Status of Predominantly Cereal-Eating Families in Pakistan

Wheat provides more than 50% of the protein and calorie intake of the population of Pakistan. Legumes and animal protein that could complement the amino acid pattern of wheat, in which lysine is the first limiting amino acid for utilization of protein, are not affordable by members of lower socioeconomic groups in developing countries. The purpose of the study was to determine whether lysine fortification of wheat flour would have a positive impact on populations consuming a predominantly wheat-based diet. A double-blind study was carried out for three months on the outskirts of Peshawar, Pakistan. Forty families received wheat flour fortified with lysine, and 40 families received wheat flour without lysine. Wheat provided 59% of the protein for men, 65% for women, and 58% for children. The weight and height of the children in both groups increased during the study, but the increase was significantly greater in the lysine group. Hemoglobin increased significantly in the women receiving lysine-fortified flour. Transferrin levels increased significantly in men, women, and children in the lysine group as compared with those in the control group. Prealbumin increased significantly in adults receiving additional lysine but decreased in children. Men, women, and children in the lysine-supplemented families had significant increases in CD4, CD8, and complement C3 as compared with controls. These results indicate that lysine fortification of wheat flour can significantly improve sensitive indicators of nutritional status in a population consuming a diet in which 58% to 65% of the protein, depending on age and sex, is supplied by wheat.

Lysine Fortification: Past, Present, and Future

Fortification with lysine to improve the protein value of human diets that are heavily based on cereals has received support from the results of these recent studies [1,2]. Support also comes from examination of average food and nutrient availability data derived from food balance sheets. Whereas nutritional status is influenced by the nutrient content of foods consumed in relation to need, the requirements for protein and amino acids are influenced by many additional factors [10, 12, 14, 28, 29]. These include age, sex, body size, physical activity, growth, pregnancy and lactation, infection, and the efficiency of nutrient utilization. Even if the immune response was influenced by the added lysine, adequate water and basic sanitation would remain essential. Acute and chronic undernutrition and most micronutrient deficiencies primarily affect poor and deprived people who do not have access to food of adequate nutritional value, live in unsanitary environments without access to clean water and basic services, and lack access to appropriate education and information [30]. A further variable is the possible interaction between protein and food energy availability [31]. This could affect the protein value of diets when food energy is limiting to a significant degree. Thus, the additional effects of food energy deficiency on protein utilization could well be superimposed on the very poorest. The improvement of dietary diversity must be the long-term aim, with dietary fortification considered only a short-term solution. The former should take place as wealth improves and the gaps between rich and poor diminish. Although such changes are taking place, they are highly uneven. Over the last several decades, increases have occurred in the availability of food energy, total protein, and animal protein for both developed and developing countries. However, for the very poorest developing countries over the same period, changes have been almost nonexistent, and the values for some nutritional indicators have even declined. For estimated lysine value, the developed countries showed increases in per capita availability from 5,400 to 6,167 mg per day and the developing countries from 2,400 to 3,454 mg per day, while in contrast, the very poorest countries remained static at about 2,400 to 2,500 mg per day. Thus, although lysine fortification may be theoretically only a short-term solution, in the very poorest countries changes in wealth such that dietary diversity and lysine availability may increase by natural progression remain remote. If we can justify using lysine to fortify animal feed in the rich regions of the world for economic gain, perhaps we should now consider adding lysine to the flour consumed by the deprived people in the poorest regions of the world to improve both their nutrition and their resistance to disease.

Contribution of intestinal microbial lysine to lysine homeostasis is reduced in minipigs fed a wheat gluten-based diet

BACKGROUND

We previously reported microbial lysine contribution to plasma lysine homeostasis in humans with an adequate lysine intake.

OBJECTIVE

We sought to explore whether the low lysine intake from a wheat gluten-based diet is balanced by enhanced microbial lysine contribution in a pig model.

DESIGN

Twenty miniature pigs (minipigs) fitted with ileo-ileal cannulas were fed 2 wheat gluten-based diets. One diet provided 2.7 g lysine/kg diet (WG diet) and one diet was supplemented with crystalline lysine to provide 6.6 g lysine/kg diet (WG+Lys diet). Both diets were fed for 10 or 100 d (n = 5 per group): 10WG+Lys, 10WG, 100WG+Lys, and 100WG diets. Ileal microbial lysine, which we considered to be the precursor pool for absorption, was labeled by oral administration of (15)NH(4)Cl for the final 10 d. On days 10 and 100, a 10-h fast-fed tracer protocol with [1-(13)C]lysine was performed.

RESULTS

Lysine rates of appearance decreased by 25% with the WG diet in the fed state but increased by 50% with the WG+Lys diet in the fasted state (P < 0.05). Daily gross microbial lysine contribution was lower (P < 0.05) with the WG diet (205.3 micro mol. kg(-) (1). d(-)(1)) than with the WG+Lys diet (370.7 micro mol. kg(-) (1). d(-)(1)), irrespective of the adaptation period and was similar to the ileal lysine loss with the WG diet. In the WG groups, incorporation of microbial lysine increased in the duodenum and liver (P < 0.05) but not in whole-body and muscle proteins.

CONCLUSION

Minipigs fed the WG diet did not adapt by showing an enhanced absorption of microbial lysine to the extrasplanchnic tissues, presumably because microbial lysine continues to be used for splanchnic protein synthesis.

Lysine requirements of healthy adult Indian subjects receiving long-term feeding, measured with a 24-h indicator amino acid oxidation and balance technique

BACKGROUND

The mean lysine requirement of healthy Indian subjects was estimated from short-term experimental diet periods to be 29 mg x kg(-1) x d(-1), which is higher than the 1985 FAO/WHO/UNU upper requirement of 12 mg x kg(-1) x d(-1).

OBJECTIVE

Our objective was to confirm our proposed requirement of 29 mg x kg(-1) x d(-1) by extending the diet period to 21 d and by using 4 test lysine intakes (12, 20, 28, and 36 mg x kg(-1) x d(-1)) and a 24-h indicator amino acid oxidation and balance approach.

DESIGN

During two 21-d diet periods, 18 healthy Indian men were randomly assigned to receive 12 and 28 or 20 and 36 mg lysine x kg(-1) x d(-1) as part of an L-amino acid diet. At 1800 on days 6 and 20, [(13)C]leucine was infused over 24 h to assess leucine oxidation and daily leucine balance at each test intake.

RESULTS

Leucine oxidation, balance, and flux did not differ significantly between days 7 and 21. Twenty-four-hour leucine oxidation was lower at lysine intakes of 28 and 36 mg than at 12 and 20 mg. Leucine balances at lysine intakes of 12 and 20 mg were negative and significantly less than equilibrium (P < 0.01) and lower (P < 0.02) than balances at 28 and 36 mg lysine. Two-phase regression analysis indicated a breakpoint at 31 mg lysine x kg(-1) x d(-1) in the relation between lysine intake and 24-h leucine oxidation and balance.

CONCLUSIONS

Full adaptation to a low lysine intake occurs within 7 d. The previously proposed tentative mean lysine requirement for Western subjects of 30 mg x kg(-1) x d(-1) is confirmed for healthy Indian adults.

Daily requirement for and splanchnic uptake of leucine in healthy adult Indians

BACKGROUND

The 1985 FAO/WHO/UNU requirement for leucine is too low according to tracer-derived estimates of leucine oxidation and balance in adults from developed regions.

OBJECTIVE

The leucine requirement in populations in developing countries was assessed with use of the 24-h tracer balance method and on the basis of nitrogen balances.

DESIGN

Twenty healthy Indian men were studied during their consumption for 6 d of 2 L-amino acid diets that supplied either 14 and 30 (n = 10) or 22 and 40 (n = 10) mg leucine x kg(-1) x d(-1) in random order. At 1800 on day 7, a 24-h constant intravenous [13C]leucine tracer-infusion protocol was conducted to determine leucine oxidation and daily leucine balance. During the intake of 40 mg leucine/d, [2H3]leucine was given orally to assess the splanchnic uptake of leucine.

RESULTS

Mean 24-h leucine oxidation rates were 29.8, 30.6, 33.6, and 39.3 mg x kg(-1) x d(-1) at leucine intakes of 14, 22, 30, and 40 mg x kg(-1) x d(-1), respectively; daily leucine balances were -16.5, -9.0, -3.3, and 0.5 mg x kg(-1) x d(-1), respectively. Mixed-models linear regression of balance against leucine intake resulted in a zero balance at a leucine intake of 37.3 mg x kg(-1) x d(-1). Nitrogen balances were -12.7, -17.9, -3.9, and 1.0 mg x kg(-1) x d(-1) at leucine intakes of 14, 22, 30, and 40 mg x kg(-1) x d(-1). Regression of nitrogen balance against intake resulted in a zero balance at a leucine intake of 37.6 mg x kg(-1) x d(-1). The first-pass splanchnic uptake of leucine was 45.7% and 33.9% in the fasted and fed periods, respectively.

CONCLUSION

A tentative mean leucine requirement of 40 mg x kg(-1) x d(-1) is proposed for healthy Indian adults, as it is for Western subjects.

Lysine requirements of healthy adult Indian subjects, measured by an indicator amino acid balance technique

BACKGROUND

In an earlier study, using a modification of the indicator amino acid oxidation approach, we concluded that the 1985 FAO/WHO/UNU-proposed lysine requirement of 12 mg x kg(-1) x d(-1) is likely inadequate to maintain body amino acid homeostasis in apparently healthy south Asian subjects and that our proposed requirement of 30 mg x kg(-1) x d(-1) is more appropriate.

OBJECTIVE

We assessed the lysine requirement in a similar population by using 4 test lysine intakes (12, 20, 28, and 36 mg x kg(-1) x d(-1)) with an indicator amino acid balance approach.

DESIGN

Sixteen healthy male Indians were studied during each of 2 randomly assigned 8-d L-amino acid diets that supplied either 12 and 28 or 20 and 36 mg lysine. At 1800 on day 8, a 24-h intravenous [(13)C]leucine tracer-infusion protocol was conducted to assess leucine oxidation and daily leucine balance at each lysine intake.

RESULTS

Mean 24-h leucine oxidation rates decreased significantly (P = 0.005) across different lysine intakes and were 104.1, 97.8, 87.3, and 87.3 mg x kg(-1) x d(-1) at intakes of 12, 20, 28, and 36 mg x kg(-1) x d(-1), respectively; mean 24-h leucine balances were 3.3, 9.1, 19.7, and 20.7 mg x kg(-1) x d(-1), respectively (P = 0.015, mixed-model analysis of variance). Oxidation and balances differed significantly between the lower and higher lysine intakes but were not significantly different between the 12- and 20-mg and 28- and 36-mg test intakes. Two-phase regression analysis indicated a mean breakpoint at 29 mg lysine x kg(-1) x d(-1) in the relation between lysine intake and leucine oxidation or balance.

CONCLUSION

We propose a mean lysine requirement of 30 mg x kg(-1) x d(-1) for healthy Indian adults, which is the same amount we proposed previously for Western populations.

The nutritional value of plant-based diets in relation to human amino acid and protein requirements

The adequacy of plant-based diets in developed and developing countries as sources of protein and amino acids for human subjects of all ages is examined. Protein quantity is shown not to be an issue. Digestibility is identified as a problem for some cereals (millet (Panicum miliaceum) and sorghum (Sorghum sp.)) and generally is poorly understood. Direct measurements of biological value in children are reviewed and scoring is considered. Various existing requirement values for amino acids and especially lysine are reviewed, and it is concluded that stable-isotope studies do not yet provide adequate alternative values of N balance data, which for lysine are robust after recalculation and adjustment. A new maintenance requirement pattern is developed, with higher values than those of Food and Agriculture Organization/World Health Organization/United Nations University (1985) but lower values than the Massachusetts Institute of Technology pattern (Young et al. 1989). Calculations of age-related amino acid requirements are based on most recent estimates of human growth and maintenance protein requirements, a tissue amino acid pattern and the new maintenance amino acid pattern. These values appear valid when used to score plant proteins, since they indicate values similar to or less than the biological value measured directly in young children. When used to score plant-based diets in India, no marked deficiencies are identified. All regions score > 1 for adults, whilst for children scores range from > 1, (Tamil Nadhu) from 6 months of age to 0.78 (West Bengal), rising to 0.9 in the 2-5 year old, consistent with reports that high-lysine maize supports similar weight and height growth to that of casein. Inadequate amino acid supply is not an issue with most cereal-based diets.

Adult human amino acid requirements

This brief review is concerned with the status of our current understanding of the quantitative needs for dietary amino acids in healthy adults. The nutritional significance of the conditionally indispensable amino acids is assessed and the requirements for the indispensable amino acids are discussed. Recent research involving the use of the tracer balance approach is reviewed, and the importance of resolving the current uncertainties regarding adult human amino acid needs is highlighted.

Metabolic demands for amino acids and the human dietary requirement: Millward and rRvers (1988) revisited

In 1988, Millward and Rivers reappraised existing metabolic models for amino acid requirements. The metabolic demand for amino acids was reviewed in relation to both obligatory metabolic consumption and adaptive pathways of amino acid oxidation. The obligatory demand pattern was deemed unknowable from first principles except that the level of one amino acid would be similar to its concentration in an amount of tissue protein equivalent to the obligatory nitrogen loss. The adaptive demand pattern was predicted to vary in relation to the amount and the periodicity of food protein intake that influenced the amplitude of the diurnal cycle of gains and losses. A regulatory influence of protein intake on anabolism, the anabolic drive, was identified in animal studies; benefit appeared to derive from intakes in excess of the minimum for balance, which could facilitate definition of an optimal requirement. The inherent and design-related limitations of both nitrogen and stable isotope balance studies of requirement were recognized as a major problem in identifying secure values for indispensable amino acid requirements. A decade of research of increasing methodological sophistication has generated much new information, confirming the adaptive diurnal model of balance regulation and allowing development of the anabolic drive into a general protein-stat theory for coordinated control of growth and maintenance of the lean body mass. However, notwithstanding several new estimates of amino acid requirement values, definition of a widely accepted human amino acid requirement pattern remains unresolved. Although a case can be made for an adjusted 1985 FAO adult requirement pattern being a reasonable estimate of the obligatory indispensable amino acid requirements for human maintenance, the problems posed by adaptation, methodological inadequacies and lack of independent measures of adequacy mean that assessment of the adequacy of the human diet to satisfy amino acid needs remains inherently difficult.

Low nutritional quality of unconventional tropical crop seeds in rats

As the search for alternative sources of food to alleviate hunger continues, this study was undertaken to determine the biological value in growing rats (BV) of proteins of some lesser known tropical seeds gathered in Nigeria. Antinutritional factors (trypsin inhibitors, phytic acid, oxalate, tannin, alkaloids) and amino acid compositions were also determined, and protein digestibility-corrected amino acid score (PDCAAS) was calculated using the amino acid requirement pattern of the preschool child and individual seed-specific correction factors for crude protein. A rat growth and balance study was conducted to determine digestibility, nitrogen-, and energy balance by feeding as the only unsupplemented protein source milled and heat-treated seeds of Adansonia digitata (Bombacaceae) and Prosopis africana, Lonchocarpus sericeus, Enterolobium cyclocarpium, Sesbania pachycarpa and Pterocarpus osun (Leguminosae) in comparison to casein fortified with methionine (control). Diets containing P. africana and L. sericeus seeds caused poor feed intake and weight loss in rats and were excluded from the nitrogen-balance test. Among the seed samples, S. pachycarpa followed by A. digitata showed the most advantageous nutritional quality [amino acid composition, digestibility, BV and net protein utilization (NPU)]. True digestibility was 82.9 and 74.5 vs. 98.5, BV was 64.6 and 70.0 vs. 90.4, and NPU was 53.5 and 52.1 vs. 89.0 for S. pachycarpa and A. digitata vs. casein (control), respectively. In terms of PDCAAS, lysine was the first limiting amino acid for S. pachycarpa (88%) and for A. digitata (58%). The PDCAAS of all essential amino acids was below 100% for E. cyclocarpium (e.g., cysteine + methionine: 37%) and for P. africana (e.g., threonine: 46%, except valine and a very high content of cysteine and methionine). In conclusion, all seeds tested in the rat balance trial were of inferior quality compared to casein. Before these tropical seeds could be used as food components or feed supplements, safety studies and proper processing to remove antinutritional factors and possible toxic constituents were required.

[Calculation of recommendations regarding protein intake: their application to preschool, school students and adults taking Brazilian foods]

The recommendations for protein consumption depend on the essential amino acid and total nitrogen content of a diet, and food digestibility. International recommendations are based on egg or milk proteins. However, populations eat different food mixtures. Brazilians use rice and beans as their main protein food source. This study presents different Brazilian diets, with variable amount of rice and beans. The results show that for each diet there is a different amount of protein recommended. Pre-school children, for example, must receive from 1.15 to 1.77 g/protein/day, depending on the mixture of their dietary protein intake. Besides the diet protein's quality and quantity, the total food intake and presence of other essential nutrients, such as iron, calcium and vitamin C has also to be considered. The correct protein recommendation with respect to a diet or a mixture of food, should take into consideration: digestibility, total nitrogen, essential amino acids, presence of others nutrients and weight of food consumed.

Linking the field to the laboratory in nutrition research

The three examples presented illustrate the dynamic way in which the field and the laboratory interact. Both types of study rely on sound research design and clear articulation of the relevant exposure. In all studies it is essential to consider the effect that measurement error will have on the estimate of the effect of the exposure on the outcome. Epidemiological studies rely on metabolic research to refine the methods and measures of nutritional exposures used in studies of cause-effect relationships. Metabolic studies rely on population studies to determine whether the experimental evidence they reveal is of public health importance. The Nutrition Society provides a vital forum within which this exchange between the field and the laboratory will continue.