Obesity
Commentary
Higher Dietary Protein During Weight Loss: Muscle Sparing? Stuart M. Phillips
In this issue, Smith et al. (1) present an eloquent trial addressing whether consumption of higher dietary protein (50% above the recommended dietary allowance [RDA]) preserves skeletal muscle mass during hypoenergetic diet-induced weight loss. Higher dietary protein has been proposed to mitigate reductions in fat-free mass (FFM) during weight loss (2). Meta-analyses have shown that higher dietary protein intake results in greater fat mass loss and a better retention of FFM in older (3) and younger persons (4). Whether the preserved FFM is skeletal muscle is unclear, but speculation has been that if the loss of FFM is muscle, then weight loss might have some disadvantageous consequences, such as placing older people at risk for sarcopenia (5). In a tightly controlled trial, groups of postmenopausal women with obesity were randomly assigned to weight loss while consuming protein at the RDA (0.8 g protein/kg/d; weight loss [WL]) or a higher protein intake (1.2 g protein/kg/d; weight loss plus protein supplementation [WL-PS]). The authors showed that muscle volume losses were greater in the WL versus WL-PS group when participants had lost 5% of their body weight, but at 10% of body weight loss, there was no statistical difference between the groups. In the short time frame of the study (6 months), there were no changes (or differences) in various composite measures of leg strength associated with the reductions in muscle mass. This is unsurprising, as the losses of muscle volume were, by the authors’ admission, small, and participants were fully mobile and weight bearing during their weight loss. Where then are we left insofar as dietary protein and weight loss are concerned? If protein is not protective against loss of muscle mass, then exercise would appear to be the most obvious adjunct during weight loss (6). The authors rightly point out that protein supplementation may not have resulted in increased retention of muscle because of the relative refractoriness of older persons to provision of protein; however, exercise would be an important addition to weight loss even if it did not enhance lean mass retention, as it would provide a multitude of health benefits besides (6). It is also
likely that exercise may have ablated the lack of change in insulin sensitivity the authors had previously reported (7). Not discounting the authors’ findings (7), it is noteworthy that a meta-analysis shows that weight loss induced by higher-protein diets is associated with health benefits, including improvements in glycemic variables, that are similar to or greater than standard protein diets (4). Interestingly, Clifton et al. also concluded that “the short-term benefit of higherprotein diets appears to persist to a small degree long term,” noting that fasting triglyceride and insulin were lower with a higher-protein (lower-carbohydrate) diet (8). Clearly, as with most science in the realm of weight loss, more work remains to be done; nonetheless, the intriguing findings of Smith et al. (1) are an important part of the puzzle.O
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References 1. Smith GI, Commean PK, Reeds DN, Klein S, Mittendorfer B. Effect of protein supplementation during diet-induced weight loss on muscle mass and strength: a randomized controlled study. Obesity (Silver Spring) 2018;26:854-861. 2. Leidy HJ, Clifton PM, Astrup A, et al. The role of protein in weight loss and maintenance. Am J Clin Nutr 2015;10:1320S-1329S. 3. Kim JE, O’Connor LE, Sands LP, Slebodnik MB, Campbell WW. Effects of dietary protein intake on body composition changes after weight loss in older adults: a systematic review and meta-analysis. Nutr Rev 2016;74:210-224. 4. Wycherley TP, Moran LJ, Clifton PM, Noakes M, Brinkworth GD. Effects of energy-restricted high-protein, low-fat compared with standard-protein, low-fat diets: a meta-analysis of randomized controlled trials. Am J Clin Nutr 2012;96: 1281-1298. 5. Phillips SM, Chevalier S, Leidy HJ. Protein "requirements" beyond the RDA: implications for optimizing health. Appl Physiol Nutr Metab 2016;41:565-572. 6. Villareal DT, Aguirre L, Gurney AB, et al. Aerobic or resistance exercise, or both, in dieting obese older adults. N Engl J Med 2017;376:1943-1955. 7. Smith GI, Yoshino J, Kelly SC, et al. High-protein intake during weight loss therapy eliminates the weight-loss-induced improvement in insulin action in obese postmenopausal women. Cell Rep 2016;17:49-861. 8. Clifton PM, Condo D, Keogh JB. Long term weight maintenance after advice to consume low carbohydrate, higher protein diets--a systematic review and meta analysis. Nutr Metab Cardiovasc Dis 2014;24:224-235.
Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada. Correspondence: Stuart M. Phillips (
[email protected]) See accompanying article, pg. 854. Disclosure: Dr. Phillips reports competitive research funding, honoraria, and travel reimbursement from the US National Dairy Council, outside the submitted work. Received: 14 March 2018; Accepted: 14 March 2018; Published online 24 April 2018. doi:10.1002/oby.22186
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Obesity | VOLUME 26 | NUMBER 5 | MAY 2018
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