Four times the Recommended Daily Allowance (RDA)! That’s how much protein the subjects of the latest study from Dr. Jose Antonio’s lab were consuming for six months during this year-long study on the safety of high protein diets.
For the other six months, their average protein intake was 2.5 grams per kg of body weight (around 1.1 gram per lb), which is still more than three times the RDA.
The safety of high protein diets
In the last few decades, the safety of high protein diets has been questioned numerous times – especially with regards to their effects on the liver and kidneys.
However, as we’ve mentioned in another article, scientific research to date suggests that high protein diets are perfectly safe for healthy individuals, with studies such as this one, this one, this one and this one showing no harmful effects of high protein diets on renal function, liver function or bone health.
Until recently, however, research on the safety of high protein diets was limited to relatively short-term studies with protein intakes that rarely exceeded 2 grams per kg of body weight.
In fact, a statement on dietary protein and weight regulation from the Nutrition Committee of the the American Heart Association (AHA) mentioned that “although these diets may not be harmful for most healthy people for a short period of time, there are no long-term scientific studies to support their overall efficacy and safety.”
Until now, that is!
Behold Dr. Jose Antonio’s year-long study on very high protein diets!
In this study, which was published in the Journal of Nutrition and Metabolism, 14 healthy resistance-trained men consumed their normal diet for six months (which was already a high protein diet) and a higher protein diet for another six months.
Their protein intake during their habitual, or normal, diets averaged 2.5 grams per kg of body weight (1.1 grams per lb) while, during the high protein diets, it significantly increased to 3.3 grams per kg of body weight (1.5 grams per lb).
With regards to caloric intake, this significantly increased from an average of 2511 calories during the habitual diets to 2919 calories during the high protein diets, while the amounts of carbs, fats, sugar, sodium, cholesterol and dietary fiber did not change significantly during the high protein phase.
With regards to the subjects’ body composition, there were no significant differences between the two phases for fat free mass or fat mass, despite a caloric increase of around 400 calories per day during the high protein diets phase.
This is, likely, because of the higher thermic effect of protein in combination with increases in the subjects’ levels of Non-Exercise Activity Thermogenesis (NEAT). Of course, since food intake was self reported, we cannot rule out under-reporting of dietary intake due to increased satiety from the large amounts of protein.
Finally, and perhaps most importantly for the purpose of this article, the subjects experienced no harmful effects with a one-year high protein diet (3-4 times the RDA) on their renal function, blood lipids, hepatic function, etc.
The authors hypothesize that this may be partially attributed to their high fiber intake (30 grams per day), which has previously been associated with a lower risk for cardiovascular disease, cancer, and all-cause mortality.
The authors go on to mention that “the cholesterol intake of our subjects was twice as high as the typical recommendation of 300 mg per day. The notion that high cholesterol intakes have a deleterious effect on blood lipid markers of cardiovascular disease is not supported by our data.”
A few limitations of the study include the small sample size (only 14 subjects), the gender (only males) as well as the fact that the subjects were engaging in resistance training throughout the study. As with any study, it’s important to take the methodology into account and to not generalize the results to everyone.
If you are a young, healthy adult, who routinely engages in resistance training to build muscle, it’s pretty safe to say that high protein intakes (up to 3.3g per kg of body weight) are safe and unlikely to negatively impact your health, provided that these take place inside the context of an overall healthy diet with sufficient levels of micronutrients and fiber.
Is there, however, a reason to increase protein that much?
Well, it depends. As we’ve mentioned in Part 2 of our How to Build Muscle series, for most exercising individuals most of the time, around 2 grams of protein per kg of lean body mass (or around 1 gram per lb of lean body mass) is plenty. We can, however, certainly make a case for benefits to higher protein intakes under certain conditions.
That’s a subject for another article, though, so we’ll just leave it at that!