Published September 25, 2021 in Current Developments in Nutrition (CDN), “A Whole-Grain Diet Increases Whole-Body Protein Balance Compared to a Macronutrient-Matched Refined-Grain Diet,” has quickly captured global attention. This original research article, authored by ASN member Jacob T. Mey et al., has already placed in the top 5% of all research outputs scored by Altmetric.
The Dietary Guidelines for Americans, 2020-2025 recommend that at least half of all grains consumed be whole grains. Unfortunately, according to the Dietary Guidelines, 98% of Americans fall below these whole-grain recommendations.
Whole grains haven’t had their bran and germ removed by milling; therefore, all of the nutrients remain intact. They are better sources of fiber and other important nutrients, such as selenium, potassium, and magnesium. Refined grains, in contrast, are milled, stripping out many nutrients, including fiber.
Among the many benefits that whole grains confer, limited data from randomized controlled trials suggest that whole grains may enhance protein metabolism. This enhanced protein metabolism may be particularly important for older adults: as we age, we tend to lose muscle mass and muscle function, the result of protein breakdown rates chronically surpassing protein synthesis rates.
Nutritional interventions designed to positively impact protein turnover by increasing protein and energy intake have shown little effect on enhancing muscle function. In response, Dr. Mey and his team of investigators wanted to know if consuming a whole-grain diet might make a difference. Specifically, the authors wanted to determine:
- Clinical effects of a whole-grain diet on whole-body protein turnover
- Cellular effects of whole grains on protein synthesis in skeletal muscle cells
- Population effects of whole-grain intake on age-related muscle loss
In order to conduct their research, the authors implemented a carefully designed three-pronged approach to gain a broad perspective on the effect of a whole-grain versus a refined-grain diet on protein turnover in adults. The core elements of this approach included a randomized controlled feeding trial, in vitro mechanistic cell culture studies, and an investigation of epidemiologic data.
Participants in the feeding trial, all adults with obesity or overweight, were randomized to follow either a whole-grain enriched or refined-grain diet for a period of eight weeks. Diets were matched for macronutrient composition and were isocaloric for each individual participant. The study diets were designed to meet dietary guidelines for macronutrient, vitamin, and mineral intake. As part of the trial, the authors tracked key cardiovascular, glucose, and protein metabolism markers.
Findings from the feeding trial revealed that “when adults with overweight/obesity consume a whole-grain diet, whole-body protein turnover and 24-hour integrated net protein balance is increased compared to a carefully matched refined-grain diet.” Specifically, the data suggest that when whole-grain intake aligns with Dietary Guideline recommendations, the equivalent of five to six servings a day, whole-body protein turnover is enhanced in adults with overweight or obesity.
In support of these findings, the authors provided additional evidence from their complementary in vitro cell culture studies, which demonstrated that “a whole-grain extract increases skeletal muscle global protein synthesis rates in response to anabolic stimuli.” Moreover, findings from the epidemiologic investigation suggested that “whole-grain intake is associated with greater muscle function in older adults.” Together, findings from this three-pronged approach “corroborate the view that whole-grain intake positively impacts short-term whole-body protein turnover with a potential to impart long-term physiologic benefits.”
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*Heather Schier is a PhD student at the Ohio State University and recently served as an ASN Science Policy Fellow.
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