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The study also looked at the effects of plant protein versus animal protein.
Ensuring adequate muscle mass and strength in lower extremities is crucial for older adults; without it, elderly people risk higher rates of falls, fractures, and other debilitating injuries. As it stands, adults begin losing 1%–2% of muscle mass each year starting at age 50. Dietary protein intake has been shown to contribute to muscle status, and now Harvard Medical School researchers are pulling data from the past to examine the role that protein intake-and different types of protein-plays in muscle mass and strength in this vulnerable population.
The researchers pulled data from the Framingham Offspring Cohort, a study started in 1971 primarily to examine risk factors of cardiovascular disease. Using cross-sectional protein-intake data from the years 1995-2001, researchers analyzed the protein intake of roughly 2600 men and women with a mean age of 59. Mean total protein intake was 80 g/day for men and 76 g/day for women. Measurements of subjects’ leg lean mass and isometric quadriceps strength were taken between the years 1996 and 2001.
Lean muscle mass in the leg was found to be highest in subjects with the highest level of total protein intake. The researchers also looked at types of protein-specifically, the effects of animal protein versus plant protein. High animal-protein intake was linked to increased muscle mass in men and women. Plant protein intake was not.
But the highest quartile of plant protein intake was initially linked to a higher level of quadriceps strength. According to researchers, muscle strength-or the lack thereof-strongly determines physical disability and mortality in older adults. But when researchers adjusted the data for fruit and vegetable intake, they no longer found a significant association between plant protein intake and muscle strength. “There could be several reasons for this observation,” they wrote, among them that “it may be difficult to isolate the effect of plant protein from other beneficial nutrients of fruits and vegetables, such as antioxidants and carotenoids.”
Overall, the researchers tout adequate protein intake as a “midlife modifiable risk factor” to lower the risk of conditions such as sarcopenia, which cost the U.S. healthcare industry an estimated $18.5 billion in 2000.
“Our findings suggest that maintaining adequate protein intake with aging may help preserve muscle mass and strength in adult men and women,” the researchers wrote. “Dietary protein types may differentially affect muscle mass and strength,” they added, noting that own observations “suggest a role for plant protein in the preservation of muscle with age.”
This study was funded in part by the National Institutes of Health.
Nutritional Outlook magazine
1. Sahni S et al., “Higher protein intake is associated with higher lean mass and quadriceps muscle strength in adult men and women,” The Journal of Nutrition, vol. 145, no. 7 (July 2015): 1569-1575.