While protein has been extensively studied in older adults, not as much is known about the relationship of amino acids and functional health outcomes in this population. This cross-sectional study characterized usual intakes of total and individual amino acids and determined associations between usual intakes and body composition, muscle strength, and physical function in U.S. adults 65 y and older utilizing the NHANES dataset from 2001-2018. Usual intakes of each essential amino acid (EAA) were above the Estimated Average Requirement (EAR) for all deciles in both males and females over the age of 65 y. Absolute (g/d) and relative (mg/kg ideal body weight/d) EAA, leucine, lysine, and sulfur-containing amino acid (SAA) intakes were not associated with body composition measures of appendicular lean mass, whole body fat mass, BMI, and waist circumference in males for the fully adjusted model. Absolute lysine intakes were positively associated with BMI (linear trends only; 3.0 ± 0.7, P < 0.0001) and waist circumference (linear trends only, 7.0 ± 1.7, P = 0.0001) in females. Absolute intakes of EAA were also positively associated with waist circumference in females (linear trends only, 2.1 ± 0.6, P = 0.0007). Relative intakes of EAA, leucine, and lysine were positively associated with BMI (linear trends only, 0.1 ± 0.02, P < 0.0001; linear trends only, 0.3 ± 0.1, P = 0.0004; 0.4 ± 0.1 per decile, P < 0.0001, respectively) and waist circumference (linear trends only, 0.2 ± 0.01, P < 0.0001; linear trends only, 0.8 ± 0.2, P < 0.0001; 0.1 ± 0.2 per decile, P < 0.0001, respectively) in females. Relative intakes of lysine were also positively associated with whole body fat mass (linear trends only, 0.2 ± 0.1, P = 0.0006) in females. Absolute and relative EAA, leucine, lysine, and SAA intakes were not associated with muscle strength measures of combined grip strength in both males and females. Self-reported physical function measures (difficulties of walking up 10 steps without resting, walking for a quarter mile, standing up from an armless chair, pulling or pulling large objects and lifting or carrying something as heavy as 10 pounds) were not associated with absolute or relative amino acid intakes in older men or women except for difficulty of pushing or pulling large objects which was negatively associated with absolute EAA, leucine, and SAA intakes in older men (-0.9 ± 0.27, P = 0.0010; -0.2 ± 0.05, P = 0.0007; -0.1 ± 0.02, P = 0.0003, respectively). Overall, individual usual amino acid intakes were above the EAR for U.S. older adults. There does not appear to be a relationship between amino acid intake and body composition in older men. Amino acid intake may be positively associated with BMI and waist circumference in older women. There is no relationship between amino acid intake and muscle strength in older men and women. There is no relationship between amino acid intake and self-reported physical function in older women. The self-reported physical function of pulling or pulling large objects may be negatively associated with amino acid intake in older men.
