New research, published in Advances in Nutrition and supported by the Institute for the Advancement of Food and Nutrition Sciences (IAFNS), makes a case for closing the gaps in protein research and suggests a framework for doing so.
“We begin by emphasizing cardiometabolic health, frailty prevention, bone health and weight management but believe this is just the beginning of expanding our understanding of how protein intake can be optimized to benefit quality of life for all,” said John Carbone, lead author on the study and professor at the School of Health Sciences at Eastern Michigan University.
The investigation brought together leading researchers from McMaster University, San Diego State University, the U.S. Army Research Institute of Environmental Medicine and the Office of Dietary Supplements at the National Institutes of Health.
Closing the gaps in protein research
To build on the decades of past protein research, Carbone et al. emphasized the need to move beyond commonly used muscle or whole-body protein turnover assessments towards the identification of appropriate outcomes and credible biomarkers to determine if and how varying intake or source affects health across the lifespan.
“For example, altering dietary protein quantity, quality (that is, essential amino acid content, digestibility and bioavailability) and source (that is, amino acids, isolated protein, protein-rich foods or protein in mixed meals) may modulate insulin sensitivity, cardiovascular disease (CVD), frailty, osteoporosis and fracture risk, appetite and obesity,” they wrote.
In the United States, the current recommended dietary allowance (RDA) for protein is based on the minimum intake required for most people of 0.8 grams per kilogram of body weight. Research on optimal protein intake across different populations and need states, however, is ongoing—with a nuanced back-and-forth among academics and nutritionists about how much protein is too little or too much.
“There’s no ceiling for protein after you get to a certain number of grams,” Douglas Kalman, co-founder of consultancy Substantiation Sciences and the International Society of Sports Nutrition (ISSN), previously told NutraIngredients in response to a viral New York Times article titled “Is Protein Powder a Scam?”.
“Your immune system is using it,” he added. “Your gut is using it. Your muscles are using it for [their] structure. Your bones are using it. The only way the body is going to stop absorbing protein is if a person defecates or throws it up.”
Barbara Lyle, consulting senior nutrition advisor at IAFNS, considers that as a minimum to prevent deficiency, the recommendation misses the opportunity to propose protein intakes that support optimal health across the lifespan.
“In order to develop protein recommendations to help achieve optimum rather than minimum health, the pipeline of research needs to focus on meaningful health outcomes that support overall health in aging,” she said.
Meaningful outcomes and credible biomarkers
Research methods to measure optimal protein intakes differ from health outcome to health outcome—whether blood pressure and plasma lipid concentrations for cardiometabolic health or a combination of bone, muscle and mobility measures for frailty.
In all cases, Lyle noted that there are many factors that must be controlled or adjusted. Beyond tracking the effects of altering timing, amount, quality and specific amino acid building blocks of protein, she noted the need to determine study length for optimal outcomes and the effects of replacing other macronutrients with protein.
Professor Carbone said that he is particularly intrigued by the prospect of muscle-bone crosstalk and the impact of dietary protein on both muscle and skeletal health, referencing a recent systematic review organized by the Department of Health and Human Services Agency for Healthcare Research and Quality. The review highlighted the limited research available on the relationship between protein intake and bone health in children and adolescents.
Weakened bones and sarcopenia are also a growing public health concerns among older adults, where diets rich in protein, particularly those with adequate levels of essential amino acids, may be key to improving outcomes. As measures, the review suggested that more sophisticated imaging technologies like MRI and CT scans could provide deeper insights into how protein affects muscle and bone health.
“Bone health indicators may be another useful tool in evaluating and refining recommendations for protein intake beyond the traditional methods,” Professor Carbone added. These might include novel biomarkers of bone formation, resorption, myokine and osteokine concentrations in biological tissues, as well as calcium isotope tracers, which can measure calcium absorption, excretion, exchange with bone and whole-body retention.
The review also proposes potential methodologies and data collection techniques for weight management outcomes that prompt researchers to consider the influence of time-dependency of protein consumption, sex-based differences, subjective hunger sensations, microbiome metabolite production, appetite-regulating hormones, sleep influences and higher-than-RDA protein intake in future studies.
“Although our related understanding has increased dramatically, translating decades of acute laboratory studies focused on muscle or whole-body protein turnover to long-term health is challenging,” the researchers noted. “As the field shifts emphasis to elucidating the role of dietary protein in supporting and sustaining human health throughout the lifespan, past research accomplishments provide a foundation for innovative thinking and an approach for the continued creation of an evidence base to best support future public health policy guidance and nutrition initiatives.”
Source: Advances in Nutrition. doi: 10.1016/j.advnut.2024.100347. “Exploring Opportunities to Better Characterize the Effects of Dietary Protein on Health across the Lifespan”. Authors: John Carbone et al.
