Quick Hit Summary
Many individuals work hard to lose weight. Unfortunately, a causality of this weight loss is lean muscle tissue. One of the ways to minimize this effect is by increasing protein intake during a time of caloric restriction. In a recent study, involving trained lean men (BMI- 23-24), eating 1 g of protein/lb/day attenuated loss of lean body tissue by 2 lbs vs. those consuming 0.45g of protein/lb/day over a 2 week period. This occurred despite both groups consuming 60% of usual caloric intake. Performance also did not suffer for these individuals.
Save Your Muscle While Losing Weight
In a previous article, Effect of Caloric Restriction and Exercise on Weight Loss and Heart Health, I discussed how equal weight loss could be achieved via dietary modifications alone or a combination of exercise + dietary changes. Unfortunately, in attempting to drop a few inches from the waistline (ie- decreasing fat mass), collateral damage, in the form of muscle breakdown, often occurs. Furthermore, the lower % body fat you have at baseline, the greater likelihood that muscle will be lost while on a caloric restricted diet1.
Figure 1 Are you really going to tell me that you don't want this meal on your diet plan9
For functional and aesthetic purposes, individuals often desire to lose fat while maintaining muscle tissue. Thus, various researchers have examined how weight loss can be maximized while still preserving as much lean muscle mass as possible. One way to offset this decline in lean muscle mass is via resistance training2. Additionally, it appears that macronutrient distribution (ie- % protein, % carbohydrates, % fat in diet) may also effect loss of lean muscle mass during times of caloric (kcal) restriction. In 2006, a large meta-analysis, which combined the results from 87 previously conducted studies, suggested that increasing dietary protein intake, in conjunction with a reduced kcal diet, preserved muscle tissue (and other fat free tissue)3. Most of the studies examining the influence protein intake has on body composition changes have focused on overweight, obese and/or individuals with preexisting health conditions4. However, few studies have examined the effects of protein on body composition in healthy, athletic populations while on a reduced kcal diet.
Influence of Dietary Protein on Body Composition in Healthy Athletes during Times of Energy Restriction
In a study completed by Walberg et al., researchers placed experienced body builders on a 1 week kcal restricted diets (51.4% of usual kcal intake). that consisted of either a high protein (0.73g/lb) or moderate protein (0.36g/lb) diets (See Figure 1 for macro distribution).5 Based off nitrogen balance tests, it appeared that those in the high protein group maintained lean tissue while on the low energy diets. This was not seen in the moderate protein group. However, those in the high protein group also experienced a 22% loss in muscular endurance in their quadriceps vs. baseline measurements. In contrast, no changes were found in the moderate protein group when comparing pre- and post-diet muscular endurance times. Despite maintaining a positive nitrogen balance, Lambert et al hypothesized that the decrease in muscular endurance of the quadriceps muscle was a result of the extreme reduction in total kcal consumption6, which potentially failed to provide enough carbohydrates to supply energy at higher intensities.
Table 1. Energy intake and percent of total energy contributed to each group by various macronutrients5. As seen below, dietary carbohydrate levels fluctuated to account for the changes in dietary protein, whereas fat content stayed relatively the same between diets.
| Group | Energy Intake (kcal/lb) | % kcal (protein) | % kcal (carbs) | % kcal (fat) |
| Moderate protein (0.36g/lb) | 8.2 kcal/lb | 17% | 70% | 13% |
| High Protein (0.73g/lb) | 8.2 kcal/lb | 35% | 50% | 15% |
In a recently published study (2010), Mettler et al. also examined the effects of dietary protein on body composition in 20 trained male athletes (mean age ~25 years; BMI ~23-24) while undergoing a 2 week diet consisting of 60% of usual kcal intake7. All participants were healthy (no reported metabolic disorders), participated in at least 2 resistance training sessions/week for >6 months and on average, exercised 4-5 times/week for a total duration of ~330-360 minutes. Participants were separated into 2 separate groups; a high (1.04g/lb) or moderate (0.45g/lb) protein group. Due to the importance of carbohydrates in supplying energy during high intensity training, Mettler et al. did not decrease the overall percentage of carbohydrates in the diet. Rather they altered the contribution that fat made to each diet as shown in Table 2.
Table 2. Energy intake and percent of total energy contributed to each group by various macronutrients7. As seen below, dietary fat levels fluctuated to account for the changes in dietary protein, whereas carbohydrate content stayed relatively the same between diets.
| Group | Energy Intake (kcal/lb) | % kcal (protein) | % kcal (carbs) | % kcal (fat) |
| Moderate protein (0.45g/lb) | 11.94 kcal/lb | 15% | 50% | 35% |
| High Protein (1.04g/lb) | 11.5 kcal/lb | 35% | 50% | 15% |
Please note that Mettler et al.7 reduced dietary energy intake to 60% of usual intake, vs. Walberg et al. who reduced it to 51.4%5. Therefore, despite having somewhat similar macronutrient distributions, those in Mettler et al.’s high protein group were consuming more total energy (and thus more protein, carbohydrates, etc) vs those in Walber et al.'s high protein group.
Results
Normal training routines were maintained during the 2 weeks of kcal restriction. At the end of the 2 week kcal restricted period, both groups experienced similar fat mass losses. However, individuals in the moderate protein group lost ~2 lbs more fat free mass (which includes lean muscle mass) than those in the high protein group.
Body composition and athletic/anaerobic performance measurements (squat jump, maximal isometric leg extension, one-repetition maximum (1RM) bench press, muscle endurance bench press, and 30-s Wingate test) were taken at baseline and at the completion of the trial7. Athletic performance measurements did not appear to suffer over this 2 week time span for either of the groups. This conflicts with the results of Walberg et al. who found a decrease in muscular endurance of the quadricep muscles5. An overall smaller kcal reduction (48.6% vs. 40%) and greater carbohydrate content of the diet employed by Mettler et al. may have accounted for this difference.
A Few Related Notes
There are a couple of things I'd like to discuss with regards to these studies. First, only males participated in this study and gender differences are something I always consider when looking at results. However, studies completed on women, albeit overweight and/or obese, have shown higher protein levels to be protective against loss of lean tissue during times of kcal restriction with8 or without9 the inclusion of a supervised exercise program.
Second, I’d also like to point out that neither of the dietary interventions employed in these 2 studies dropped carbohydrate content less than 50% of overall kcal consumption. Individuals in the study by Mettler et al. still consumed ~1.5 grams of carbohydrates/lb once kcal intake was reduced to 60% of usual consumption.
Finally, I must point out that this study was only 2 weeks in duration. Thus, one must be careful in how they extrapolate these results (performance and body composition) out to longer time duration. Despite these limitations, this study provides strong evidence that consuming higher protein levels, during times of caloric restriction (60% of usual intake), minimizes the loss of muscular tissue.
Bottom Line
When losing any significant amount of weight, it’s unrealistic to think that some of the loss won’t be in the form of muscle. This is even truer in thin individuals who have lower initial % body fat prior to weight loss. For non active individuals, losing 2-3 pounds of lean muscle tissue, along with 8-10 lbs of body fat, may not seem like a large deal. However, for active individuals and/or competitive athlete, maximizing fat loss while minimizing muscle loss is often desired.
In conclusion, collateral damage, in the form of muscle breakdown, commonly occurs when reducing one’s weight. When decreasing kcal intake, be sure to still consume ~1 gram of protein/lb of body weight. In turn, these measures will help minimize potential muscle breakdown, assisting you in acquiring the body you desire!
References
1 Forbes GB. Body fat content influences the body composition response to nutrition and exercise. Ann N Y Acad Sci. 2000 May;904:359-65.
2 Stiegler P, Cunliffe A.The role of diet and exercise for the maintenance of fat-free mass and resting metabolic rate during weight loss. Sports Med. 2006;36(3):239-62.
3 Krieger JW, Sitren HS, Daniels MJ, Langkamp-Henken B. Effects of variation in protein and carbohydrate intake on body mass and composition during energy restriction: a meta-regression 1. Am J Clin Nutr. 2006 Feb;83(2):260-74.
4 Stiegler P, Cunliffe A.The role of diet and exercise for the maintenance of fat-free mass and resting metabolic rate during weight loss. Sports Med. 2006;36(3):239-62.
5 Walberg JL, Leidy MK, Sturgill DJ, Hinkle DE, Ritchey SJ,Sebolt DR. Macronutrient content of a hypoenergy diet affects nitrogen retention and muscle function in weight lifters. Int J Sports Med. 1988;9(4):261–6.
6 Lambert CP, Frank LL, Evans WJ. Macronutrient considerations for the sport of bodybuilding. Sports Med. 2004;34(5):317-27.
7 Mettler S, Mitchell N, Tipton KD. Increased protein intake reduces lean body mass loss during weight loss in athletes. Med Sci Sports Exerc. 2010 Feb;42(2):326-37.
8 Layman DK, Evans E, Baum JI, Seyler J, Erickson DJ, Boileau RA Dietary protein and exercise have additive effects on body composition during weight loss in adult women. J Nutr. 2005 Aug;135(8):1903-10.
9 Image created by Mike Johnson – TheBusyBrain.com. Accessed on June 14, 2010 from:www.flickr.com/photos/thebusybrain/2885879361/
10 Archive Image created by FotoosVanRobin. Accessed on June 19, 2010 from: www.flickr.com/photos/fotoosvanrobin/3182238046/