Dr. Jose Antonio has put out some truly novel research looking at high-protein diets. I’m not talking about the arbitrary 30% of calories that can vary widely depending on energy intake. Rather, I’m talking about grams per unit of bodyweight – as it should be.

Previous research by Dr. Antonio had shown that taking a group of healthy resistance-training men and women and having them increase their protein intake from 2.3 to 4.4 g/kg (1 to 2 g/lb) had no effect on body composition. This study was followed up with another study that showed that consuming 3.4 g/kg (1.5 g/lb) had a more favorable effect on body composition than consuming 2.3 g/kg (1 g/lb) when combined with a structured resistance training program. This latter study also showed no signs of harmful effects from a basic metabolic panel.

Now, Antonio et al have published the third study digging into this rabbit hole. This is the first randomized, crossover trial to investigate the effects of a true high-protein diet. The crossover design means that each subject serves as their own control group, thus reducing a lot of the confounding that may accompany having different groups of people experience different interventions.

The who, what, and how

The study involved 12 highly experienced resistance-trained males (~8 years of training experience with an average 1-RM bench press of 1.5 times their bodyweight). These individuals took part in two 8-week interventions in which they continued living their life and following their own training routines, except that during one of the periods they consumed more protein.

The protein was obtained primarily from whey protein powder that the researchers provided free of charge, although it is important to note that none of the participants were required to use the protein powder if they didn’t want to. All the participants had experience using the food-tracking app, MyFitnessPal, and were required to use it to log their food intake for 2 weekdays and 1 weekend day every week.

Performance testing (1-RM bench press and repetitions to failure at 60% the 1-RM), body composition assessment (Bod-Pod), and blood chemistry (blood lipids and comprehensive metabolic panel) were assessed at baseline and after each 8-week period.

Guess what? Nothing happened!

Ultimately, there were significant differences in total calorie and protein intake between baseline intakes, the normal protein group, and the high protein group. The high protein group consumed about 500 more kcal per day than the other groups and had an average protein intake of 3.3 g/kg, compared to 2.3 g/kg at baseline and 2.6 g/kg in the normal protein group. Carbohydrate and fat intake remained unchanged.

Despite the above differences, there were no significant differences between the normal and high protein groups for body composition and performance testing. That said, it is notable that 9 of the 12 participants showed a reduction in body fat mass. Additionally, fat-free mass remained stable among the majority, except for 2 subjects in which it increased. These findings are certainly in-line with those of previous research from Dr. Antonio’s lab. It is possible that the small sample size limited the ability to detect statistically significant differences (one of the limitations of this research).

As for the blood analysis, there were no changes in any of the variables. Even when examining the 2 participants with the highest recorded protein intakes (4.66 and 6.59 g/kg/day), there was no sign of any detrimental impact on renal function or blood chemistry in either individual.

A truly high-protein diet is safe and may benefit body composition

In my previous article on the optimal amount of protein to eat, I addressed the idea of protein toxicity (“rabbit starvation”). I highly recommend you at least read that section of the article, as the idea that a high protein intake is harmful to the bones, the kidneys, and overall health is not supported by the literature. The current study adds to that conclusion.

On that note, the study population is an important caveat to the current study findings. They consumed ~30 grams of fiber daily, had a low-sugar diet (50-60 g/day), and were exercising regularly. Something I brought up in my aforementioned article is that protein toxicity may be mitigated by resistance training (because the amino acids are used for repairs) and an alkaline diet (helps offset the acidic urea load). Therefore, the current findings may not apply to the average Joe couch potato snacking on chips and dip.

So why didn’t body composition change despite the added calories? It could simply be that that the high protein diet group experienced a combination of increased thermic effect of food and non-exercise activity thermogenesis such as fidgeting. Combined, these would increase total energy expenditure to match the new intake level. Alternatively, there is recent rodent data to suggest that a high protein intake may inhibit the ability of the liver to synthesize fat, possibly by stimulating ketogenesis.

Collectively, this and the two previous studies by Dr. Antonio suggest that a high protein intake, upwards of 483-724 % of the RDA, does not have a harmful effect when the individual is engaged in resistance training. Taken in conjunction with my previous article on optimal protein intake, I would also add that consuming a fiber-sufficient, alkaline diet is another important component to offsetting potential negative effects.

I acknowledge that 8 weeks is not a long time, and I know there will be criticism regarding this. I would certainly hope so, anyways, as it is indeed an important limitation. Still, blood chemistry changes within weeks, and if nothing occurred after 8, then why would we expect changes to occur later on? Regardless, I look forward to the year-long follow-up study that is currently in the works by Dr. Antonio.

So with no harm, is there any benefit? Probably not to muscle mass or strength, as those didn’t change in any of the studies from Dr. Antonio’s lab. However, fat mass may decrease, which ultimately improves body composition and health.