The effects of a high protein diet on indices of health and body composition – a crossover trial in resistance-trained men.
Antonio et al. (2016)
A high protein diet is extremely popular in the fitness industry. This is one of the first studies to examine the correlation between high protein intake and the effect on body composition and other markers of health, whilst coupled with a resistance training program.
A group of resistance-trained males underwent 2 x 8 week trials, whereby they consumed their normal protein intake, followed by a high protein intake ( > 3 g/kg/day; equal to about 200 – 250g of protein a day).
The aim of this study was to assess whether a high protein intake affected health markers, such as liver and kidney function, body composition and performance in resistance trained subjects.
In the normal protein group participants consumed around 2.6 g/kg/day, this equates to approximately 175 – 200g of protein a day; whereas in the higher protein trial participants consumed around 3.3 g/kg/day, equating to about 230 -250g of protein a day.
Over the 16 week trial period, the average protein intake was around 2.9 g/kg/day. Therefore, the average intake over the 16 week period was around 200 – 230g day. Other than the high protein group consuming more calories (approximately 400 more), there were no other differences in carbohydrate or fat intake.
For performance, there was no significant difference between groups when performing a 1-RM bench press strength test or muscular endurance test (RTF at 60 % of the 1-RM bench press).
Although for body composition the study states there were no significant differences between groups, on an individual level, the graph below shows that despite the high protein group eating around 400 additional calories, 8 of the participants showed a slight decrease in fat mass when consuming higher protein compared to their normal protein diet.
Figure 1: Individual changes in fat mass.
Summary / Key Takeaways:
This is one of the first studies to show that consuming over four times the recommended daily protein intake has no negative effects on health as demonstrated by the participants’ blood results. This supports numerous other studies that show consuming a higher than normal protein intake does not negatively affect kidney, liver or other health markers (in healthy individuals).
This study also highlights that once protein is above 2 g/kg/day, there are minimal differences in muscle gains or performance.
However, the most interesting take-away from this study is that the high protein group ate on average 400 more calories than the normal protein group, yet the majority gained no additional fat. This may make a very high protein diet (> 3 g/kg/day) suitable for higher calorie periods or bulks, when still try to minimize fat gain. It’s also a great tool to use after a contest or long diet when trying to build calories back up whilst minimizing fat gains.
It is important to note that even the normal protein intake levels were significantly higher than an average person’s intake (200g compared to around 50g for a normal individual). This may explain why there were no significant differences in body composition between the two groups.
Past studies investigating the effect of protein intake on body composition have compared a low protein intake of around 0.8 g/kg/day (equal to around 60g of protein per day) and a higher protein group and found a positive effect on body composition. You can read a full research review on high vs low protein intake for fat loss here.