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).
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
References
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