Successful Dieting [2/5]: Protein Intake

A large volume of human clinical data supports increased dietary protein for favorable changes to body composition.

One systematic review concluded that in studies where a higher protein intervention was deemed successful there was, on average, a 58.4% g/kg/day between group protein intake spread versus a 38.8% g/kg/day spread in studies where a higher protein diet was no more effective than control (1). The average change in habitual protein intake in studies showing higher protein to be more effective than control was +28.6% compared to +4.9% when additional protein was no more effective than control (1).

It is clear that protein intakes above the RDA (0.8g/kg) between 1.3-1.8g/kg can promote lean mass gains and strength from resistance training and attenuate lean mass loss during energy deficits (2). Protein intakes substantially greater (2.3–3.1 g/kg/day FFM) can also offset lean mass losses in athletes (3). 

In a study with 19 weight lifters attempting to achieve a low body fat while maintaining fat free mass, subjects were divided into a control group with moderate-protein (0.8 g/kg) high-carbohydrate hypoenergy diet (MP/HC), or high-protein (1.6 g/kg), moderate-carbohydrate hypoenergy diet (HP/MC). Using nitrogen balance, results indicated that the higher protein diet was more effective in retaining lean body mass than a diet with higher carbohydrate but the RDA for protein (4). In fact the lower protein diet (RDA) was in negative nitrogen balance (-3.19g/day) while the higher protein/lower carb diet was in a positive nitrogen balance (4.13g/day).

Fifteen normal weighted women involved in recreational resistance training and aerobic training were recruited and randomized into two groups. The 1 KG group (n = 8; energy deficit 1100 kcal/day) was supervised to reduce body weight by 1 kg per week and the 0.5 KG group (n = 7; energy deficit 550 kcal/day) by 0.5 kg per week, respectively. Protein intake was kept at least 1.4 g/kg body weight/day for both groups and the weight reduction lasted four weeks (5).

After 4 weeks total body mass, fat mass and fat percentage were decreased in both groups,  but no changes in lean body mass and bone mass were observed. The 1 KG group lost more fat (-3.8kg) than the 0.5 KG group (-2kg) (5). There were no differences in performance changes between 1 KG and 0.5 KG after the 4-week period but in 1 KG maximal strength in bench press decreased. Vertical jumping performance is improved mainly due to decreased fat and body weight, and because a greater body mass was lost in the 1 KG group the decrease in maximal bench press was also somewhat expected.

Another study examined the interaction of 2 diets (high protein, reduced carbohydrates vs. low protein, high carbohydrates) with exercise on body composition and blood lipids in 48 women during weight loss for 4 months (6). Diets were equal in total energy (7.1 MJ/d; 1700kcal), consisted of 30% of energy as fat, but differed in protein content and the ratio of carbohydrate:protein at 1.6 g/kg and <1.5 (PRO group) vs. 0.8 g/kg and >3.5 (CHO group), respectively. The low carbohydrate diet was never below 130 g/d of carbohydrates. They compared lifestyle activity (control) vs. a supervised exercise program (5 d/wk walking and 2 d/wk resistance training).

Subjects in the PRO and PRO + EX groups lost more total weight and fat mass and tended to lose less lean mass than the CHO and CHO + EX groups. Exercise increased loss of body fat and preserved lean mass. Resulted showed that the combined effects of diet and exercise were additive for improving body composition, and that a diet with higher protein and reduced carbohydrates combined with exercise additively improved body composition during weight loss (6).

In contrast comes a study by Pasiakos et al., with physically active military personnel, that found that lean mass retention tended to be greater in a group consuming 1.6 g/kg/day versus a group consuming 2.4 g/kg/day (7). In this study subjects received protein diets of 0.8g/kg (RDA), 1.6 g/kg (2x RDA) and 2.4 g/kg (3x RDA) for periods of 21 days with 40% of energy deficit.

Dietary protein intake remained constant, and was provided as mixed, high-quality proteins (e.g., dairy, lean meats, and vegetable-based proteins). Dietary fat accounted for no more than 30% of total energy, and carbohydrate provided the remainder of the prescribed energy.

The 2x RDA group lost more fat mass (70.1%) followed by the 3x RDA (63.6%), and then RDA (41.8%). Lean body mass loss was lower for the 2x RDA (29.9%) followed by the 3x RDA (36.4%) compared to RDA (58.2%). Results indicated then that the 2x RDA with 1.6g/kg lost more body fat and the less lean body mass and was better in both regards than 3x RDA (7).

This study clearly showed that consuming twice the amount of dietary protein than the RDA measurably protects FFM and promotes the loss of body fat during short-term weight loss. This study also demonstrated that consuming dietary protein three times the current RDA fail to confer further fat free mass protection or protein metabolic advantage during short-term weight loss. Levels as high as 2.4 g/kg are likely unnecessary and a plateau may exist above which consuming more dietary protein confers no additional benefit (7).

In a previous study dietary protein at 2.3 g/kg was superior to 1.0 g/kg for the maintenance of FFM in response to a 2-wk, 40% ED in young athletes who maintained their habitual training (8). Subjects consuming 1.0 g/kg (8) study did not appear to achieve that plateau. Although there were no differences between groups in either fat loss (-1.2 kg) or performance measures, the normal-protein group experienced a significant loss of lean mass (-1.6 kg), while the high-protein group almost preserved lean mass (-0.3 kg). 

Consistent with the nitrogen adaptation hypothesis, the energy cost of protein metabolism may contribute to the preservation of FFM in higher protein diets. Nitrogen and FFM may be spared at the expense of body fat due to the metabolic cost of exogenous protein catabolism.

Under rigorous experimental conditions in a metabolic ward, higher protein diets have been shown to result in more lean mass (9). While a low protein diet (5%) resulted in loss of LBM (-0.70 kg), a normal protein diet (15%) resulted in a gain of 2.87 kg LBM and a higher protein diet (25%) resulted in a gain of 3.18 kg LBM. With the low protein diet, more than 90% of the extra energy was stored as fat and with the normal and high protein diets only about 50% of the excess energy was stored as fat with most of the rest consumed (thermogenesis). There were no significant differences between energy intake and energy expenditure between the 3 diets.

The metabolic advantage of higher protein diets above the RDA during weight loss on FFM can be attributed to the energetics of protein metabolism, protein-sparing effects on lean body mass and protein-induced modulations in postprandial muscle protein synthesis (10,11).

Previously I have discussed the importance of exercise in sparing lean body mass while dieting, next time I will explore the combined effects of calorie restriction, higher protein diet and exercise.

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Summary of 34 articles with 36.528 words and 1121 references on
Exercise and nutrition

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2. Churchward-Venne TA, Murphy CH, Longland TM, et al. Role of protein and amino acids in promoting lean mass accretion with resistance exercise and attenuating lean mass loss during energy deficit in humans. Amino Acids. 2013;45:231–40.
3. Helms ER, Zinn C, Rowlands DS, et al. A systematic review of dietary protein during caloric restriction in resistance trained lean athletes: a case for higher intakes. Int J Sport Nutr Exerc Metab. 2013;24:127–38.
4. Walberg JL, Leidy MK, Sturgill DJ, et al. Macronutrient content of a hypoenergy diet affects nitrogen retention and muscle function in weight lifters. Int J Sports Med. 1988;9:261–6
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7. Pasiakos SM, Cao JJ, Margolis LM, et al. Effects of high-protein diets on fat-free mass and muscle protein synthesis following weight loss: a randomized controlled trial. FASEB J. 2013;27:3837–47.
8. Mettler S, Mitchell N, Tipton KD (2010). Increased protein intake reduces lean body mass loss during weight loss in athletes. Med Sci Sports Exerc 42(2):326–337. doi:10.1249/MSS.0b013e3181b2ef8e
9. Bray, G. A., Smith, S. R., de Jonge, L., Xie, H., Rood, J., Martin, C. K., Most, M., Brock, C., Mancuso, S., and Redman, L. M. (2012). Effect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial. JAMA 307, 47–55
10. Layman, D. K., Boileau, R. A., Erickson, D. J., Painter, J. E., Shiue, H., Sather, C. & Christou, D. D. (2003) A reduced ratio of dietary carbohydrate to protein improves body composition and blood lipid profiles during weight loss in adult women. J. Nutr. 133:411-417.
11. Bistrian, D. R., Winterer, J., Blackburn, G. L., Young, V. & Sherman, M. (1977) Effect of a protein-sparing diet and brief fast on nitrogen metabolism in mildly obese subjects. J. Lab. Clin. Med. 89:1030-1035.