Can high protein help conserve muscle mass and decrease fat mass during weight loss? And if so, what is the right amount that should be consumed? A recent paper published in 2013 discusses a study that looks into these very questions. The RDA is set at .8g per kg of body weight per day, the study evaluates body composition of participants as they consume diets of various protein levels during weight loss. The findings in this paper support that consuming protein at levels above the RDA can help to preserve fat-free mass during short-term weight loss (1).
In this randomized controlled experimental trial, 39 physically active volunteers (with BMI between 22 and 29) were assessed. A weight-management period of 10 days was then followed by a 21 day energy deficit of 40%. Each volunteer was randomly assigned to one of three diets providing protein at the recommended dietary allowance (RDA) of 0.8g/kg, 2X-RDA (1.6), and 3X-RDA (2.4). The dietary protein intakes were kept constant during the weight-management phase as well as the energy deficit phase. During the 21 day energy deficit phase, participants consumed a diet that reduced their energy intake by 30% and increased their physical activity to expend 10% more energy than in the weight management phase. During both phases, body composition and protein synthesis were measured. At the end of the study, participants had lost an average of 3.2 kg of body weight regardless of which diet they consumed, however, those who received the 2X-RDA and 3X-RDA when compared to the RDA had a lower proportion of weight loss due to decreases in fat-free mass (p < 0.05) and had a higher loss of fat mass (p < 0.05). The protein building response after a high protein meal was lower during energy deficit than weight management for the participants consuming protein at the RDA level (p < 0.05), but for the 2X-RDA and 3X-RDA diets the protein building response showed no difference (p > 0.05). They also found that the loss of fat-free mass versus fat mass was no different between the 2X-RDA and 3X-RDA diets.
One main strength of this study is that it is an experimental design, because of this cause and effect can be observed. From this study, a conclusion can be drawn that eating a diet above the RDA in times of energy deficiency can help to keep fat-free mass. The fact that there is no difference between the 2X-RDA and 3X-RDA diets indicates that there is a plateau and that there is an optimal level of protein to help shield fat-free mass. Another strength of this study is that it was randomize, insuring that the results wouldn’t be biased. There are a few limitations of this study however. One limitation is that the study only lasted for 31 days, so these findings can only be applied to short-term, moderate energy deficiency. Another limitation is that the population was very specific, military personal and civilians with a BMI of 22-29, physically active and without any prior medical issues. While this did help to control confounding factors during the study, it makes it hard to generalize these findings to everyone, especially with this relatively small sample size. It is true however, that this sample size is larger than those used in various other studies that have assessed similar diets.
The idea of high protein diets are popular right now as a promising strategy to achieve weight loss. A potential mechanism to account for this is that protein increases secretion of satiety hormones such as GIP and GLP-1 and decreases hormones that stimulate hunger such as ghrelin (2). In previous studies done on this topic of ideal protein level it has been shown that diets intended to loose weight that were higher in protein resulted in a higher loss of fat when compared to diets high in other nutrients (3). This study went on to build on that by comparing levels of protein and determining the optimal level of protein to achieve this. A possible mechanism for this FFM-conserving effect may be related to alterations in protein turnover that are induced by diet and protein (Phillips, 2008). In a previous study done by Paskios (4) the findings concluded that in short term energy deficiency in normal-weight adults down regulates muscle protein synthesis. This could be an adaptive mechanism to conserve energy and protein reserves in times of food deprivation. One of the important findings in this study is that those receiving the 2X-RDA were able to conserve Fat-Free Mass, while those receiving the 3X-RDA had no additional benefits. In a previous study of Mettler et al. it was shown that consuming a greater amount of protein during energy deficiency can help to conserve fat free mass, but they did not try levels about 2x the RDA (5). Thus, one of the important findings in this study is that those receiving the 2X-RDA were able to conserve Fat-Free Mass, while those receiving the 3X-RDA had no additional benefits, indicating a plateau.
While there are a few limitations of this study, for the most part it provides strong evidence that an increase of protein to 2x the RDA during energy restriction will help to conserve muscle and help you to loose fat more efficiently. It also shows that increasing the level of protein above that of 2X the RDA provides no additional benefit. This can help those who are trying to lose weight and want to improve their body composition as well. This study was an experimental, randomized controlled trial from which a cause and effect relationship can be drawn. Based on this study, when trying to cut back on calories, increasing your protein intake and your level of exercise can be beneficial.
Reference List
1. Pasiakos S, Cao J, Young A, et al. Effects of high-protein diets on fat-free mass and muscle protein synthesis following weight loss: a randomized controlled trial. FASEB Journal [serial online]. September 2013:27(9):3837-3847. Available from Academic Search Premier, Ipswich, MA. Accessed February 4, 2015. Accessed at: http://www.fasebj.org.dist.lib.usu.edu/content/27/9/3837.full.pdf+html
2. Pesta D, Samuel V. A high-protein diet for reducing body fat: mechanisms and possible caveats. Nutrition & Metabolism [serial online]. December 2014: 11(1):1-17. Available from: Academic Search Premier, Ipswich, MA. Accessed February 5, 2015.
3. Layman D, Boileau R, Christou D, et al. A Reduced Ratio of Dietary Carbohydrate to Protein Improves Body Composition and Blood Lipid Profiles during Weight Loss in Adult Women. Journal of Nutrition [serial online]. February 2003:133(2):411-417. Available from: Academic Search Premier, Ipswich, MA. Accessed February 4, 2015.
4. Pasiakos S, Vislocky L, Rodriguez N, et al. Acute Energy Deprivation Affects Skeletal Muscle Protein Synthesis and Associated Intracellular Signaling Proteins in Physically Active Adults. Journal of Nutrition [serial online]. April 2010:140(4): 745-751. Available from: Academic Search Premier, Ipswich, MA. Accessed February 4, 2015
5. Mettler S, Mitchell N, Tipton K. Increase Protein Intake Reduces Lean Body Mass Loss during Weight Loss in Athletes. Medicine & Science In Sports & Exercise [serial online]. February 2010:42(2):326-337. Available from Academic Search Premier, Ipswich, MA. Accessed February 5, 2015.
Reviewed by Viktoriya Wolff
