What Happens When You Eat "Too Much" Protein?
If you throw yourself into the research (or, alternately, ask a hundred lifters), you probably won't come up with an exact answer as to what the optimal amount of protein is for muscle growth. But if you threw out the outliers and averaged out the rest of the estimates, you'd probably get something along the lines of 1.5 to 2 grams of protein per kilogram.
Fair enough, but what happens when you exceed that number by a bunch? Oddly enough, it turns out that despite getting a bunch of extra calories, lifters who bumped up their protein intake considerably actually lost body fat.
To see what would happen when lifters eat more than the generally accepted optimum amount of protein, Dr. Joey Antonio performed an 8-week study on 48 recreational (but experienced) bodybuilders. Each of them reported to have taken in about 2 grams of protein per kilogram every day for the last few years.
Antonio and his colleagues split the group in two. The first group stayed on the same protein intake (NP). The second group increased their daily protein intake to 3.4 g per kilogram per day. All of the subjects performed the same training program.
Despite their instructions, the NP group, perhaps subconsciously, increased their protein intake slightly to 2.3 g per kilogram, higher than the 2 grams mandated by the researchers.
Perhaps surprisingly, both groups, the 2.3 g "low" protein group and the 3.4 g high protein group, gained the same amount of muscle mass. However, the really high protein group ended up losing much more fat mass, even though they were taking in about 400 more calories a day!
The NP group lost an average 0.3 kg of fat, but the HP group, despite the extra caloric intake, lost an average of 1.6 kg of fat. Percent body fat decreased, too. The percent body fat decrease was -2.4% in the HP group and -0.6% in the NP group.
How could this happen? Dr. Antonio's group had some theories. They speculated that it might have something to do with the thermic effect of protein or TEF. A high-protein meal (about 45% of the total calories in that meal) has about a 30% greater TEF than a low-protein meal (about 15% of the total calories in that meal).
The researchers also suggested that the fat loss could be a combination of TEF, AEE (activity related energy expenditure), and NEAT (non-exercise related energy expenditure).
Regardless of the actual cause, the study had three main findings:
- Protein overfeeding is unlikely to cause any gains in body fat, and appears to actually reduce body fat.
- It's wrong to conclude that eating anything more than 1.5 to 2.0 g per kilogram of protein is a waste of time.
- Blood tests confirmed that a high-protein intake had no detrimental effects to the kidneys or any other parameters of health.
- Antonio J et al. A high protein diet (3.4 g/kg/d) combined with a heavy resistance training program improves body composition in healthy trained men and women – a follow up investigation. J Int Soc Sports Nutr. 2015 Oct 20;12:39. PubMed.