Can We Define Dietary Requirements of Dispensable Amino Acids?

A discussion on the 'dispensable' amino acids

PURPOSE OF REVIEW

Recently, the concept of dietary dispensable amino acids has been increasingly challenged, as more indirect and direct (experimental) evidence has pointed to the need for them in the diet during specific life stages or disease states. Here, we discuss the classification of amino acids, methods to assess the needs for dispensable amino acids with experimental evidence from our recent studies, and highlight the role of specific dispensable amino acids in metabolism and health.

RECENT FINDINGS

There exist differences among the dispensable amino acids to act as effective nitrogen sources in humans. Glycine, a dispensable amino acid is conditionally indispensable in later stages of human pregnancy.

SUMMARY

The so-called 'dispensable' amino acids are quantitatively nearly 75% of the daily protein needs in humans. In certain life-stages and diseases, there is a dietary demand for the dispensable amino acids. Future well-designed studies are required to identify the dietary demand for these amino acids, which will certainly be useful for dietary management in specific diseases and to maintain health across all life-stages.

Adequacy and Sources of Protein Intake among Pregnant Women in the United States, NHANES 2003-2012

Limited information is available on protein intake and adequacy of protein intake among pregnant women. Using data from a sample of 528 pregnant women in the National Health and Nutrition Examination Surveys (NHANES) 2003–2012, usual intake of protein (g/day and g/kg body weight (bw)/day) and prevalence of intake below the Estimated Average Requirement (EAR) by trimester of pregnancy were calculated using the National Cancer Institute method. Percent contributions to protein intake by source (i.e., plant and animal, including type of animal source) were also calculated. Mean usual intake of protein was 88 ± 4.3, 82 ± 3.1, and 82 ± 2.9 g/day among women in trimester 1, 2, and 3 of pregnancy, respectively, or 1.30 ± 0.10, 1.35 ± 0.06, and 1.35 ± 0.05 g/kg bw/day, respectively. An estimated 4.5% of women in the first trimester of pregnancy consumed less protein than the EAR of 0.66 g/kg bw/day; among women in the second and third trimesters of pregnancy, 12.1% and 12.8% of women, respectively, consumed less protein than the EAR of 0.88 g/kg bw/day. Animal sources of protein accounted for approximately 66% of total protein. Findings from this study show that one in eight women in the second and third trimesters of pregnancy have inadequate intake of protein. Pregnant women should be encouraged to consume sufficient levels of protein from a variety of sources.