Current issues in determining dietary protein and amino-acid requirements

Understanding the role of the gut in undernutrition: what can technology tell us?

Gut function remains largely underinvestigated in undernutrition, despite its critical role in essential nutrient digestion, absorption and assimilation. In areas of high enteropathogen burden, alterations in gut barrier function and subsequent inflammatory effects are observable but remain poorly characterised. Environmental enteropathy (EE)-a condition that affects both gut morphology and function and is characterised by blunted villi, inflammation and increased permeability-is thought to play a role in impaired linear growth (stunting) and severe acute malnutrition. However, the lack of tools to quantitatively characterise gut functional capacity has hampered both our understanding of gut pathogenesis in undernutrition and evaluation of gut-targeted therapies to accelerate nutritional recovery. Here we survey the technology landscape for potential solutions to improve assessment of gut function, focussing on devices that could be deployed at point-of-care in low-income and middle-income countries (LMICs). We assess the potential for technological innovation to assess gut morphology, function, barrier integrity and immune response in undernutrition, and highlight the approaches that are currently most suitable for deployment and development. This article focuses on EE and undernutrition in LMICs, but many of these technologies may also become useful in monitoring of other gut pathologies.

Milk products in the dietary management of childhood undernutrition - a historical review

The present narrative review outlines the use of milk products in infant and young child feeding from early history until today and illustrates how research findings and technical innovations contributed to the evolution of milk-based strategies to combat undernutrition in children below the age of 5 years. From the onset of social welfare initiatives, dairy products were provided by maternal and child health services to improve nutrition. During the last century, a number of aetiological theories on oedematous forms of undernutrition were developed and until the 1970s the dogma of protein deficiency was dominant. Thereafter, a multifactorial concept gained acceptance and protein quality was emphasised. During the last decades, research findings demonstrated that the inclusion of dairy products in the management of severe acute malnutrition is most effective. For children suffering from moderate acute malnutrition the evidence for the superiority of milk-based diets is less clear. There is an unmet need for evaluating locally produced milk-free alternatives at lower cost, especially in countries that rely on imported dairy products. New strategies for the dietary management of childhood undernutrition need to be developed on the basis of research findings, current child feeding practices, socio-cultural conditions and local resources. Exclusive and continued breast-feeding supported by community-based nutrition programmes using optimal combinations of locally available complementary foods should be compared with milk product-based interventions.

The Rise and Fall of Protein Malnutrition in Global Health

BACKGROUND

From the 1950s to the mid-1970s, United Nations (UN) agencies were focused on protein malnutrition as the major worldwide nutritional problem. The goal of this review is to examine this era of protein malnutrition, the reasons for its demise, and the aftermath.

SUMMARY

The UN Protein Advisory Group was established in 1955. International conferences were largely concerned about protein malnutrition in children. By the early 1970s, UN agencies were ringing the alarm about a 'protein gap'. In The Lancet in 1974, Donald McLaren branded these efforts as 'The Great Protein Fiasco', declaring that the 'protein gap' was a fallacy. The following year, John Waterlow, the scientist who led most of the efforts on protein malnutrition, admitted that a 'protein gap' did not exist and that young children in developing countries only needed sufficient energy intake. The emphasis on protein malnutrition waned. It is recently apparent that quality protein and essential amino acids are missing in the diet and may have adverse consequences for child growth and the reduction of child stunting. Key Messages: It may be time to re-include protein and return protein malnutrition in the global health agenda using a balanced approach that includes all protective nutrients.

Human Protein and Amino Acid Requirements

Human protein and amino acid nutrition encompasses a wide, complex, frequently misunderstood, and often contentious area of clinical research and practice. This tutorial explains the basic biochemical and physiologic principles that underlie our current understanding of protein and amino acid nutrition. The following topics are discussed: (1) the identity, measurement, and essentiality of nutritional proteins; (2) the definition and determination of minimum requirements; (3) nutrition adaptation; (4) obligatory nitrogen excretion and the minimum protein requirement; (5) minimum versus optimum protein intakes; (6) metabolic responses to surfeit and deficient protein intakes; (7) body composition and protein requirements; (8) labile protein; (9) N balance; (10) the principles of protein and amino acid turnover, including an analysis of the controversial indicator amino acid oxidation technique; (11) general guidelines for evaluating protein turnover articles; (12) amino acid turnover versus clearance; (13) the protein content of hydrated amino acid solutions; (14) protein requirements in special situations, including protein-catabolic critical illness; (15) amino acid supplements and additives, including monosodium glutamate and glutamine; and (16) a perspective on the future of protein and amino acid nutrition research. In addition to providing practical information, this tutorial aims to demonstrate the importance of rigorous physiologic reasoning, stimulate intellectual curiosity, and encourage fresh ideas in this dynamic area of human nutrition. In general, references are provided only for topics that are not well covered in modern textbooks.

Protein requirements of healthy pregnant women during early and late gestation are higher than current recommendations

BACKGROUND

Adequate maternal dietary protein intake is necessary for healthy pregnancy. However, current protein intake recommendations for healthy pregnant women are based on factorial calculations of nitrogen balance data derived from nonpregnant adults. Thus, an estimate of protein requirements based on pregnancy-specific data is needed.

OBJECTIVE

The objective of this study was to determine protein requirements of healthy pregnant women at 11-20 (early) and 31-38 (late) wk of gestation through use of the indicator amino acid oxidation method.

METHODS

Twenty-nine healthy women (24-37 y) each randomly received a different test protein intake (range: 0.22-2.56 g · kg(-1) · d(-1)) during each study day in early (n = 35 observations in 17 women) and late (n = 43 observations in 19 women) gestation; 7 women participated in both early and late gestation studies. The diets were isocaloric and provided energy at 1.7 × resting energy expenditure. Protein was given as a crystalline amino acid mixture based on egg protein composition, except phenylalanine and tyrosine, which were maintained constant across intakes. Protein requirements were determined by measuring the oxidation rate of L-[1-(13)C]phenylalanine to (13)CO2 (F(13)CO2). Breath and urine samples were collected at baseline and isotopic steady state. Linear regression crossover analysis identified a breakpoint (requirement) at minimal F(13)CO2 in response to different protein intakes.

RESULTS

The estimated average requirement (EAR) for protein in early and late gestation was determined to be 1.22 (R(2) = 0.60; 95% CI: 0.79, 1.66 g · kg(-1) · d(-1)) and 1.52 g · kg(-1) · d(-1) (R(2) = 0.63; 95% CI: 1.28, 1.77 g · kg(-1) · d(-1)), respectively.

CONCLUSIONS

These estimates are considerably higher than the EAR of 0.88 g · kg(-1) · d(-1) currently recommended by the Dietary Reference Intakes. To our knowledge, this study is the first to directly estimate gestational stage-specific protein requirements in healthy pregnant women and suggests that current recommendations based on factorial calculations underestimate requirements. This trial was registered at clinicaltrials.gov as NCT01784198.