While some diets load up on protein and other diets dictate protein sources, it can be hard to know what to consume while managing weight or during weight loss.
A new study by Purdue University nutrition scientists shows that eating more protein daily than what is recommended may benefit only a few - those who are actively losing weight by cutting calories or those strength training to build more lean muscle mass. This study also affirms that the recommended dietary allowance, of 0.8 grams of protein per kilogram of body weight per day - or 0.36 grams per pound - is adequate for most people. For example, an adult who weighs 150 pounds should eat 54 grams of protein a day, which could be three ounces of lean meat, three cups of dairy and one ounce of seeds or nuts within a day.
"But here is the hard part for consumers: These findings support that most adults who are consuming adequate amounts of protein may only benefit from moderately higher protein intake when they are purposefully trying to change their body composition such as when dieting or strength training. The results are not meant to encourage everyone to increase their protein intake in general," said Wayne Campbell, a professor of nutrition science, whose research integrates exercise physiology, geriatrics and nutrition, especially protein.
The study was led by Joshua L. Hudson, Purdue postdoctoral research associate, and it is published in Advances in Nutrition.
"This research uniquely assesses whether adults benefit from consuming more protein than the current recommended dietary allowance," Hudson said. "This research was not designed to assess whether or not adults would benefit from consuming more protein than they usually consume. This distinction is important because the recommended dietary allowance is the standard against which to assess nutrition adequacy; however, most adults consume more protein than what is recommended."
When people are in a neutral metabolic state - not losing weight or lifting weights - eating more protein does not influence their body composition any differently, including lean mass, which is consistent with the current recommended dietary allowances being adequate for generally healthy sedentary weight-stable people. This does not include adults with Type 2 diabetes.
"And that is important because there is so much encouragement, advertising and marketing for everyone to eat higher protein diets, and this research supports that, yes, under certain conditions, including strength training and weight loss, moderately more protein may be helpful, but that doesn't mean more is needed for everybody at all times," Hudson said.
More than 1,500 nutrition articles were screened across journal databases to identify 18 studies with 22 intervention groups and 981 participants that addressed this topic. The studies were selected based on specific factors including inclusion of healthy adults, protein intake, weight loss and physical activity. The sources of protein evaluated included lean and minimally processed meats, dairy, eggs, nuts, seeds and legumes.
"This research is clinically more important for women and especially older women who are known to typically consume lower amounts of protein and should be maintaining a healthy bodyweight and regularly strength training," Campbell said.
What do these findings mean for someone watching their weight during the holidays or planning New Year's resolutions?
"If you are going to start losing weight, don't cut back across all foods you usually consume, because you'll inadvertently cut back protein. Instead, work to maintain, or even moderately increase, protein-rich foods. Then, cut back on the carbs and saturated fat-containing foods," said Campbell, who studies how sources and amounts of protein - which is critical to building muscle mass - may be a part of adopting healthy eating patterns, including the Mediterranean diet and DASH diet.
These findings are in general, and more evaluation is needed to determine effects on age and gender. This research does not apply to elite athletes or people who lost weight with bariatric surgery, nor does it relate to protein supplements.
No external funding was used for this study. Campbell's lab continues to study the influences of healthy eating patterns and diets with different amounts and sources of protein on changes in body composition and clinical health risk factors.
Protein Intake Greater than the RDA Differentially Influences Whole-Body Lean Mass Responses to Purposeful Catabolic and Anabolic Stressors:
A Systematic Review and Meta-analysis
Joshua L Hudson, Yu Wang, Robert E Bergia III, and Wayne W Campbell
Under stressful conditions such as energy restriction (ER) and physical activity, the RDA for protein of 0.8 g · kg?1 · d?1 may no longer be an appropriate recommendation. Under catabolic or anabolic conditions, higher protein intakes are proposed to attenuate the loss or increase the gain of whole-body lean mass, respectively. No known published meta-analysis compares protein intakes greater than the RDA with intakes at the RDA. Therefore, we conducted a systematic review and meta-analysis to assess the effects of protein intakes greater than the RDA, compared with at the RDA, on changes in whole-body lean mass. Three researchers independently screened 1520 articles published through August 2018 using the PubMed, Scopus, CINAHL, and Cochrane databases, with additional articles identified in published systematic review articles. Randomized, controlled, parallel studies ?6 wk long with apparently healthy adults (?19 y) were eligible for inclusion. Data from 18 studies resulting in 22 comparisons of lean mass changes were included in the final overall analysis. Among all comparisons, protein intakes greater than the RDA benefitted changes in lean mass relative to consuming the RDA [weighted mean difference (95% CI): 0.32 (0.01, 0.64) kg, n = 22 comparisons]. In the subgroup analyses, protein intakes greater than the RDA attenuated lean mass loss after ER [0.36 (0.06, 0.67) kg, n = 14], increased lean mass after resistance training (RT) [0.77 (0.23, 1.31) kg, n = 3], but did not differentially affect changes in lean mass [0.08 (?0.59, 0.75) kg, n = 7] under nonstressed conditions (no ER + no RT). Protein intakes greater than the RDA beneficially influenced changes in lean mass when adults were purposefully stressed by the catabolic stressor of dietary ER with and without the anabolic stressor of RT. The RDA for protein is adequate to support lean mass in adults during nonstressed states. This review was registered at http://www.crd.york.ac.uk/prosperoasCRD42018106532.
Advances in Nutrition