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.
Losing fat while gaining muscle is generally considered the holy grail of dieting. Unfortunately, the vast majority of weight loss studies show that as much as 20-30% of the body weight lost during dieting is from lean body mass (including muscle mass). Maintenance of muscle mass is important for everyone, but becomes particularly relevant when athletes are trying to lose weight while improving performance, as well as for older adults due to the importance of muscle mass for overall health and mobility.
Resistance training is one of the most important factors for maintaining muscle mass while dieting, with other major ones shown in Figure 1. It can attenuate the loss of muscle by stimulating muscle protein synthesis (MPS). And it’s also been well established that protein supplementation can augment the effects of strength training on MPS. However, the optimal protein intake to promote weight loss while retaining and/or increasing muscle mass has yet to be firmly determined.
Being in an energy deficit appears to reduce basal MPS, as well as the sensitivity of MPS from feeding. However, a resistance training program along with increased protein intake can synergistically increase rates of MPS. This is particularly valuable during an energy deficit, as one study showed consuming 30 grams of protein after resistance exercise led to a greater stimulation of MPS than the consumption of 15 grams of protein. Another study found that 1.6 grams of protein per kilogram of bodyweight (2x the Recommended Dietary Allowance, or RDA) was able to reduce the loss of lean body mass during energy restriction, while yet another study suggested that more than two grams per kilogram of bodyweight may be needed to maintain lean mass when dieting.
Beyond resistance training, high-intensity interval training during a calorie deficit can also help to retain lean mass. A further consideration is the effects of an energy deficit on hormone levels, with or without exercise. Hormones such as IGF-1 and testosterone may play a role in the maintenance of lean mass during an energy deficit combined with physical activity, though this remains somewhat of an open question.
With questions still remaining about the optimal protein intake and exercise regimens during an energy deficit, researchers designed a four-week study with participants undergoing an approximate 40% caloric reduction along with daily resistance or interval training, while consuming either moderate or higher protein intakes of 1.5x and 3x the RDA for protein. Changes in body composition, hormone levels, and indices of strength and aerobic capacity were measured. Unfortunately, measures of metabolic rate were not made either before or after the intervention.
Retention of lean body mass is important when dieting. Increased protein intake and resistance training can help preserve lean mass during a calorie deficit. This study was set up to test two different protein intakes consumed by people in a caloric deficit and following a daily exercise program.
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.
This four-week, single-blind, randomized trial provided 40 men with hypocaloric diets (40% energy reduction) that were either lower protein (1.2 g/kg/day) or higher protein (2.4 g/kg/day), while undergoing exercise training six days per week. 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).
Additionally, both groups had similar increases in strength as well as anaerobic and aerobic exercise capacity. Similar changes were seen between groups for all blood hormone levels, some of which would be considered favorable changes. There were decreases in total and free testosterone as well as in insulin and IGF-1, while increases were observed in growth hormone, ghrelin, and cortisol. Only the PRO group had an increase in blood urea nitrogen and estimated glomerular filtration rate, which tells us the kidneys are excreting the additional byproducts of protein metabolism.
Cortisol is a hormone that receives a lot of attention as the “stress hormone,” and is capable of inhibiting muscle synthesis, increasing muscle breakdown, and increasing fat mass (particularly visceral fat). Accordingly, there was a significant negative relationship between changes in cortisol and increases in lean body mass, with increasing cortisol levels leading to mildly smaller increases in lean body mass. There was also a relationship between cortisol and changes in fat mass, with smaller increases in cortisol levels being mildly associated with greater decreases in fat mass.
After the four-week intervention, both groups experienced similar weight loss, but lean body mass increased more in the PRO group than the CON group, while fat loss was greater in the PRO group compared with the CON group. All measures of performance improved similarly between groups.
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.
The big picture
It has been proposed that athletes in a caloric deficit require higher than normal protein intakes, with greater intakes being required for greater calorie deficits. Non-athletes who are exercising while in an energy deficiency would likely have similar needs, and the results of this study are generally in accordance with previous research (as depicted in Figure 3).
A four-month study in overweight women following a resistance training program during a calorie deficit found that the group consuming 1.3 grams of protein per kilogram of bodyweight per day gained more lean mass and lost more fat mass than people consuming 0.8 grams per kilogram. A similar study used a 21-day energy deficit of 40% with protein intake at the RDA as well as twice (1.6 grams per kilogram) and three times (2.4 grams per kilogram) the RDA, and had participants perform low to moderate-intensity endurance and resistance exercise. The participants on the moderate protein diet (1.2 grams per kilogram) retained a substantial amount of lean body mass. However, they still did lose some muscle mass and there was no additional benefit for lean body mass with the higher protein intake (2.4 grams per kilogram). Another study that also used a 40% calorie reduction for two weeks found that neither 1.0 or 2.3 grams of protein per kilogram were able to prevent the loss of lean body mass in athletes. However, the higher protein group had much smaller losses (-1.6 kilogram vs. -0.3 kilograms).
Potential reasons for the differences between study outcomes include the type of exercise intervention (and the fact that the current study used supervised training sessions), the type of body composition analysis (this study used a Bod Pod as opposed to DEXA), the post-workout protein timing, and the fact that the athletes maintained their habitual training program while participants in this new study went from light exercise to training hard. A very recent three-month study put 80 overweight and obese women on an energy restricted diet (about 1200 kcal) that included varying amounts of protein (0.7, 0.9, and 1.3 grams per kilogram of bodyweight). All groups lost weight that came from fat mass as well as fat-free mass, but the highest protein group showed the greatest improvements in blood lipid values. Exercise was encouraged, but it was not the structured training that participants in this study undertook. This is noteworthy because similar to adherence to diet programs, adherence to unsupervised exercise advice is often poor as well.
While the assumption is that changes in lean mass occur due to the protein intake, any diet that shifts protein intake will lead to changes in the other macronutrients by default. This study used 15% protein, 50% carbohydrate, 35% fat for the CON group, and 35% protein, 50% carbohydrate, 15% fat for the PRO group. This was due to the important role that carbohydrate plays in performance and recovery. Consecutive days of intense training while consuming a diet that is inadequate in carbohydrate can severely diminish muscle glycogen stores, leading to disturbances in the hypothalamic-pituitary axis along with a decline in athletic performance and even worsened mood. This decline in performance and mood can be mitigated by a higher carbohydrate intake, so the decision to maintain a relatively higher carbohydrate intake in this study seems justified. It is also possible, but not likely, that the difference in fat intake is what was responsible for the different results seen between the two groups.
Researchers observed hormonal changes, as would be expected when doing vigorous activity in a calorie deficit. Previous research has observed that changes in IGF-1 correlated with changes in fat mass, however that was not the case in this study. Cortisol, which generally opposes fat loss and promotes muscle catabolism, behaved as expected and was significantly correlated negatively with both fat loss and muscle gain.
Researchers addressed some of the typical challenges of free-living studies by providing the participants with all of their food and beverages and supervising all training sessions. Also noteworthy is the fact that this was a single-blind study. The paper states that the analysis was done in a blinded manner, but it is unclear why the researchers conducting the sessions were not also blinded, which introduces a potential for bias.
Results of this study are generally in line with previous research, though an increase in lean body mass during such a drastic calorie reduction has not typically been seen before. Reasons for this may include the fact that, unlike other studies mentioned, they were utilizing heavy training as well as a rigorous protocol to ensure both a high protein intake and adherence to the exercise regimen.
Frequently asked questions
Would the results be the same during a longer study?
This was a four-week study, and it is unclear if a longer time period would continue the increased trend in body composition improvements. One study found that increasing protein intake during a weight maintenance phase was indeed helpful for preventing weight regain. A longer diet duration could make the effects of cortisol more relevant, to the point of undoing some of the positive changes seen in body composition. Future studies of a longer duration could measure hormone levels along with body composition at various time points, and examine if there is a time point when results plateau. It is possible that periodic refeeding during a longer program would be helpful as well.
Would even higher protein be better?
Perhaps, though there is not a lot of research on very high protein intakes during a calorie deficit. Several recent studies using very high protein intakes of 3.3 g/kg, 3.4 g/kg, and 4.4 g/kg have shown interesting results with regard to body composition, however the subjects were not in a caloric deficit.
We have a more expansive article on how much protein you do need to eat - more is not always better.
What should I know?
Overweight young men consumed a high protein or moderate protein diet during a 40% calorie reduction diet, while performing high intensity exercise six days per week, for four weeks. The high protein group (three times the RDA for protein, or 2.4 grams per kilogram of bodyweight) was able to increase lean body mass, while the moderate protein group (1.5x the RDA, of 1.2 grams per kilogram) was able to preserve, but not increase, their lean mass. Both groups lost the same amount of weight, but the high protein group was also able to lose more fat mass.
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