Does high-protein intake help when dieting?
We analyze a study which suggests that a higher protein-intake while dieting can help you lose more fat.
Who and what was studied?
Forty overweight men (mean of 23 years old, BMI 29.7, body fat 24.2%) participated in this single-blind study.
Participants were recreationally active, performing some type of physical activity once or twice a week, but not following any kind of structured resistance or aerobic training. The participants had not been training, but had a training history (e.g. former rugby or hockey players). A group with an average pre-test 1RM bench press of over 100 kilograms is not an 'untrained' population.
Participants were randomly assigned to one of two groups, both of which had a 40% reduction in energy intake compared with their estimated requirements (this is a very large daily deficit!). A control group (CON) consumed 1.2 grams of protein per kilogram of bodyweight (about 2284 kcal; 15% protein, 50% carbohydrate, 35% fat), and the higher protein group (PRO) consumed 2.4 grams of protein per kilogram (about 2409 kcal; 35% protein, 50% carbohydrate, 15% fat).
All meals were provided to the participants throughout the four-week intervention. Additionally, both groups received beverages containing whey protein to be consumed immediately after training sessions. The amount of carbohydrate in the drinks was similar between groups (about 45 grams), though the amount of protein was greater in the PRO group than the CON group (49 grams vs. 15 grams). Participants were not aware of the group they were assigned to, and the post-workout drinks accounted for over 90% of the daily macronutrient differences between groups.
An important aspect of this study was the six days of rigorous exercise sessions every week, which included:
Two days of a full body resistance training circuit (10 reps/set for three sets at 80% of the participant’s one repetition max, with the last set of each exercise to volitional failure and one minute rest between sets)
Two days of high intensity interval training (one session of four to eight 30 second cycling sprints with four minutes of rest between sets, and one session of 10 sprints for one minute with one minute of active recovery)
One day of a 250-kJ cycling time trial (about 20 minutes)
One day of a plyometric bodyweight circuit
Additionally, participants were given a pedometer and instructed to accumulate at least 10,000 steps per day. If they reported less than 10,000 steps for two consecutive days, they were told to complete a greater number of steps in the following days to ensure their average daily steps were at least 10,000. Body composition, measures of strength and aerobic capacity, and blood markers were measured before and after the intervention.
What were the findings?
The primary study findings are shown in Figure 2. Both groups lost weight (about 3.5 kilograms), and there were no differences in the amount lost between the groups. However, while lean body mass (including muscle) remained unchanged throughout the study in the control group, it increased in the high-protein group (+1.2 kilograms). This increase was also significant in comparison to the control group . This means that both groups lost fat mass, but the fat losses were greater in the PRO group (-4.8 kilograms) than the CON group (-3.5 kilograms).
What does the study really tell us?
This study is very encouraging because it shows that people can lose weight while gaining muscle mass. While the recommended daily intake of protein in the U.S. is 0.8 grams per kilogram, consuming three times that amount was more effective for improving body composition than consuming 1.5x that amount.
This study highlights the importance of increased protein intake in combination with resistance training for improving body composition, in particular maintaining lean mass, during weight loss. These subjects were in a 40% caloric deficit while undergoing a very active exercise routine. Participants had six supervised exercise sessions per week in addition to walking 10,000 steps per day. Finally, the participants were provided with a post-exercise whey protein shake. Whey protein has been shown to be better than other protein sources at stimulating muscle protein synthesis, and the post-workout window may provide optimal timing for muscle rebuilding.
However, as noted in an interview with one of the researchers, the drastic caloric deficit caused the participants to became somewhat obsessed with food after just one week of the study, and they were talking about and thinking about food constantly. This suggests that some (or all) of the weight loss may have been undone once the participants returned to a setting where they could eat freely. While this doesn’t negate the importance of the findings, it shifts the potential focus to short-term interventions (e.g. physique competitions, preparing for physical activity testing in police or firefighter academies, etc.) rather than as a sustainable long-term model of weight-loss.
