Amino acid requirements: quantitative estimates.

Abstract

There are now several direct experimental methods that are available to measure indispensable amino acid (IAA) requirements. In all these, increasing intakes of amino acids are given until a change is observed in the response curve. The response could be nitrogen (N) balance or growth, although current methods measure amino acid oxidation or its surrogate by the use of stable isotope tracers. N balance or growth progressively increase until the requirement level of intake of the IAA is reached, after which it plateaus. Oxidation of the test IAA is measured as the primary route of loss of that amino acid, such that the IAA balance (intake-oxidation) can be measured. For oxidation, there is no change in response as graded levels of the IAA are fed below the requirement level. However, once the requirement level is reached there is a linear increase in oxidation. The IAA balance follows the same pattern as the N balance. However, both these methods have several requirements and assumptions, and are technically demanding. A third method has also been developed, related to measuring the oxidation of a selected amino acid whose kinetics are well described, in response to graded intakes of the test IAA. The selected amino acid (other than the test IAA) is called an indicator amino acid, and its oxidation (or balance) response is measured. The oxidation of the indicator, particularly in the fed state, is an index of protein synthesis, and will fall as increasing levels of the test IAA are fed until the requirement level is reached, after which there is no further change. The advantage of this method is that it is relatively non-invasive, and effectively is a breath test, since the oxidation of the tracer-labelled amino acid itself acts as a surrogate for whole-body amino acid oxidation. A modification of the indicator amino acid oxidation method relates to using the measured IAA balance as a surrogate for N balance, in 24-h indicator amino acid balance (IAAB) studies. Here, the balance response follows the same pattern as that of N balance and growth. The indicator amino acid oxidation (and balance) technique is now used primarily in both developed and developing countries, to derive estimates of amino acid requirements in humans. Values of IAA requirements based on the direct and indicator amino acid oxidation and balance (IAAO and IAAB) techniques are considerably higher than those derived from N balance studies, and these tracer-based estimates are now the basis of the recent WHO et al. (2007) recommendations for amino acid requirements.

Carbon Footprints for Food of Animal Origin: What are the Most Preferable Criteria to Measure Animal Yields?

“…Therefore one of the main goals of animal husbandry is the production of food of animal origin. Such food contributes substantially to meeting the human requirements in essential amino acids (e.g., [ 74 , 75 , 76 ]) because of the high content in essential amino acids (such as lysine, methionine and cysteine, threonine, leucine, etc. ; see [ 77 ]).…”

Dairy Cow Health and Greenhouse Gas Emission Intensity

“…Food, and especially protein of animal origin can be considered the main objective of animal husbandry, apart from other performances (power, fertilizer, skins, bones, sport, entertainment, etc.). On the one side, products of animal origin contribute substantially to meet human requirements Dairy 2020, 1 of amino acids, minerals, and vitamins [5][6][7][8][9], and they have an important enjoyment value. For a better comparison of animal yields, Table 1 shows the yields of edible protein depending on animal species/production categories and performance of animals.…”

Challenges for Plant Breeders from the View of Animal Nutrition

“…As vegans demonstrate, there is no essential need for food of animal origin, if the human diets are supplemented with all essential nutrients. However, on the other hand, the consumption of meat, fish, milk and eggs may contribute significantly to meeting the human requirements for amino acids [26,[31][32][33][34][35] and some important trace nutrients (such as Ca, P, Zn, Fe, I, Se, and Vitamins A, D, E, and B12), especially for children and juveniles, as well as for pregnant and lactating women [36]. Human nutritionists [37,38] have recommended that about one-third of the daily protein requirements (0.66-1 g per kg body weight) [34,37,[39][40][41][42] of adults should originate from protein of animal origin.…”