Greater intake of total EAAs may not improve physical function in older adults

“We hypothesized greater intake of total EAAs would be associated with greater muscle strength, physical function and appendicular lean mass and reduced whole-body fat mass, waist circumference and BMI,” wrote study authors Claire Berryman and Susan Cheung, both affiliated with Florida State University and Pennington Biomedical Research Center. 

Researchers Victor Fulgoni III of Nutrition Impact, Harris Lieberman of the U.S. Army Research Institute of Environmental Medicine (USARIEM) and Stefan Pasiakos, now director of the Office of Dietary Supplements at the National Institutes of Health (and chief of USARIEM Military Performance Division at the time of the study), also contributed to the investigation. 

"Our group has conducted a series of studies investigating the relationships between protein intake and cardiometabolic health measures," Dr. Berryman told NutraIngredients-USA. "We wanted to extend this research by investigating the relationships between specific essential amino acids (EAAs) and cardiometabolic health and physical function in older Americans. As adults age, they consume fewer calories and have a reduced capacity to build muscle. Therefore, in this population, optimizing dietary EAA intake may be particularly important." 

The work was supported by the non-profit Institute for the Advancement of Food and Nutrition Sciences (IAFNS) Protein Committee, the U.S. Army Medical Research and Development Command (USAMRDC) and the Department of Defense Center Alliance for Nutrition and Dietary Supplements Research.

How much EAA intake is needed?​

Consumption of dietary protein at levels above the Recommended Dietary Allowance (RDA; 0.8 g/kg body weight per day) has been proposed as a dietary strategy to maintain lean mass and physical function, particularly given the reduced energy intake and muscle anabolic resistance to ingested nutrients in older adults. The researchers emphasized the quality over quantity of the protein source based on digestibility and EAA content—the primary stimulus for muscle protein synthesis. 

“[I]n older adults, dietary EAA intake may be associated with health and functional outcomes, independent of total protein intake,” they wrote, adding that findings from interventional studies to date are unclear and that these studies typically provide a specific dose of EAAs to participants, which is not representative of their habitual EAA intake, for a prescribed period in addition to their normal eating pattern. 

“More protein or EAA intake is needed to stimulate muscle protein synthesis (MPS) to the same extent in older adults as it does in younger adults, a phenomenon known as anabolic resistance,” the researchers wrote. “However, improvements in lean body mass and function are not consistently demonstrated in longer-term intervention studies supplementing protein and/or EAA in older adults.”

In addition to total EAA, the study assessed individual relationships between habitual consumption of leucine, lysine and total sulfur-containing amino acids (SAAs) and the designated endpoints, hypothesizing that greater intakes would each be associated with better outcomes.

Study details​

The cross-sectional study extracted data from the National Health and Nutrition Examination Survey (NHANES) 2001–2018 to determine individual usual intakes (IUIs) of total EAAs, leucine, lysine and SAAs in a cohort of 10,843 adults 65 years and older.

Data from the dietary intake assessment component of NHANES—What We Eat in America (WWEIA)—was combined with the Food and Nutrient Database for Dietary Studies (FNDDS) to generate gram amounts and determine nutrient values. To access existing amino acid composition data for the nutrient values of the foods, the researchers linked the FNDDS to the U.S Department of Agriculture Standard Reference database. 

Muscle strength measured by isometric grip test, body mass index (BMI), waist circumference, dual-energy X-ray absorptiometry-measured appendicular lean mass and whole-body fat mass and self-reported physical function (activities of daily living) served as primary outcomes.

“Habitual EAA, leucine, lysine and SAA intakes, covaried with physical activity level and usual protein intake, were not associated with lean mass, muscle strength or physical function in adults ≥65 y,” the researchers reported. “However, EAA intakes, particularly lysine, were positively associated with measures of adiposity in older females.”

The study also considered the discrepancies between current study findings and previous NHANES analyses​ performed by members of the research group that found that increases in total protein intake and protein intakes from both animal and plant sources were associated with reduced adiposity in U.S. adults. 

While the researchers noted that factors such as variability in amino acid composition and the way in which protein compared with amino acid intakes were expressed may contribute to discrepant determinations, they suggested that age may be the biggest driver.

A previous study in a 19-and-older population​ reported a positive correlation between waist circumference and age, however the current study reported an inverse relationship in the 65 and older population. There were also no correlations observed between BMI and age in the younger population, but they were inversely related in the older adults. 

“It should be considered that greater adiposity in the ≥65 y population may be protective, as higher body mass in older age has been associated with lower mortality rates,” the researchers wrote. “Furthermore, in those ≥19 y, age was positively associated with plant protein intake and negatively associated with animal protein intake.”

“Discrepancies between analyses lend justification for precision nutrition efforts,” they added.

For future study, Dr. Berryman said that analyses will focus on evaluating whether the absolute quantity of lysine in the diet or dietary patterns with high lysine content is driving the relationship with adiposity.

Source: Current Developments in Nutrition​
doi: 10.1016/j.cdnut.2024.104411​
“Associations between Essential Amino Acid Intake and Functional Health Outcomes in Older Adults: Analysis of the National Health and Nutrition Examination Survey, 2001–2018”
Authors: Susan Cheung et al.