Latest Study Shows that a 3.3 g/kg High-Protein Diet is Safe -- And Yes, This Means it Doesn't Hurt Your Kidney or Liver

Don't forget that meat and dairy are not the only good sources of protein in your diet. In fact, even vegan athletes can - albeit with some effort - follow a diet that's so high in protein that traditionalists would say it may put your kidney and liver on the line - plant protein, or not...
Guest post by Alex Leaf ( - There is a pervasive myth among vegans and health professionals alike that a high-protein diet is harmful, particularly for the kidneys. This is despite the World Health Organization official report on protein stating that "the most widely quoted potential problems relate to renal function and damage, but as discus-sed above the evidence for such claims in otherwise healthy individuals does not stand up to scrutiny" (WHO. 2016).

Still, the vast majority of protein safety data that we have is with intakes less than 2.0 g/kg bodyweight. And for most people, that is all the data we need, because most people don’t eat more than their weight in grams of protein. But there are exceptions, with the biggest probably being athletes.
High-protein diets are much safer than pseudo-experts say, but there are things to consider...

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It is very common for athletes to eat more than 2.0 g/kg of protein in attempts to maximize performance and/or body composition. Two previous studies by Dr. Jose Antonio have suggested that eating a high-protein diet (>3.0 g/kg) has no harmful side-effects over the 8-week intervention periods (Antonio. 2015 & 2016a). However, we still lack long-term data on high-protein diet safety. Or I should say, we did lack this data until Dr. Antonio published his fourth study this week in the Journal of Nutrition and Metabolism (Antonio. 2016b).
Figure 1: Comparison of habitual and experimental diet of the subjects (Antonio. 2016).
In Dr. Antonio’s latest study, 14 resistance-trained men consumed their habitual diet or a high-protein diet each for a two-month and a four-month period (six months total spent on each diet). The extra protein on the high-protein diet phase was supplied mainly from whey protein, although the participants were allowed to eat whatever they wanted to hit their protein quota.
What's a guest post and who's Alex Leaf? Many of you will already know that Alex Leaf is a good friend of mine, who has recently turned his passion for nutrition, training and supplementation into a profession and opened his own business, Leaf Nutrition - obviously not before amassing a range of titles from certified personal trainer to the Master of Nutrition and certifications as nutritionist from the state of Washington and the International Society of Sports Nutrition. Future coaching requests should thus better go to Alex than me, after all, he has the time, the education and the patience to work with clients I have never had (those of you who asked me if I do coaching will know that).
Food intake was monitored with the smartphone app, MyFitnessPal, for which all the participants had experience using, and each participant followed their own strength training program.

As we can see in Figure 1 above, the men were already consuming a relatively high protein diet, with a habitual intake of 2.5 g/kg. Yet, this significantly increased to 3.3 g/kg during the high-protein phase, leading to a significant 16% increase in caloric intake. Carbohydrate, fat, cholesterol, sodium, sugar, and fiber intake were not significantly different between phases. There were no significant differences between the habitual and high-protein groups in any measure of health or body composition, including blood lipids and a comprehensive metabolic panel (renal function, liver health, etc.).

Putting the results into perspective

One thing you should remember about the study at hand is that its subjects were athletes. As you may remember from the article "The Insulin / Glucagon Ratio and Why Diabetics and People W/ Severe Insulin Resistance Must be Careful With Protein" (read it) that the results could be very different for (obese) T2DM patients.
This is the first randomized controlled trial that has examined the effects of a high protein diet in resistance-trained men over a one-year period. Aside from the countless anecdotal evidence, this is the best evidence we currently have to suggest that consuming 3-4 times the RDA is safe in athletes.

Now, we could nit-pick and say that the sample size was too small and that the study is applicable only to male athletes, or even that one year isn’t long enough considering that chronic kidney disease can take years to decades to develop. And these are valid arguments. However, other populations outside of individuals regularly exercising are not likely to be interested in consuming this level of protein, nor would they need to, so the need to apply this data to other populations may be a moot point.

As for the length of the study, we must consider this alongside the fact that athletes have been eating this level of protein for most of their lives and are healthier than people eating less protein. Although anecdotal evidence isn’t ideal, it isn’t worthless either, especially when it exists in the vast quantities that we observe with the athletic population.
Antonio et al. are only one group of researchers dabbling w/ the health and physique advantage of really high protein diets | more.
So what is the practical takeaway? Eating up to 3.3 g/kg or 1.5 g/kg of protein appears to be safe so long as you are training regularly and have a relatively healthy, well-balanced diet providing adequate fiber (30 g average in this study | previous studies show links of high fiber intakes w/ kidney and liver health | Xu. 2014, Kirpich. 2015, Arslanow. 2016).

And even if "young, healthy and active" doesn't sound like you, there are studies like Brinkworth (2004), Clifton (2008), and Dumesnil (2001) that show weight loss benefits and identical or improved health parameters compared to "regular" / lower protein diets | Comment on Facebook!
  • Antonio J, Ellerbroek A, Silver T, 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; 12: 39. PMID: 26500462
  • Antonio J, Ellerbroek A, Silver T, Vargas L, Peacock C. The effects of a high protein diet on indices of health and body composition--a crossover trial in resistance-trained men. J Int Soc Sports Nutr. 2016a; 13: 3. PMID: 26778925
  • Antonio J, Ellerbroek A, Silver T, et al. A high protein diet has no harmful effects: a one-year crossover study in resistance-trained males. J Nutr Metab. 2016b
  • Arslanow, Anita, et al. "Short-Term Hypocaloric High-Fiber and High-Protein Diet Improves Hepatic Steatosis Assessed by Controlled Attenuation Parameter." Clinical and Translational Gastroenterology 7.6 (2016): e176.
  • Brinkworth, G. D., et al. "Long-term effects of a high-protein, low-carbohydrate diet on weight control and cardiovascular risk markers in obese hyperinsulinemic subjects." International journal of obesity 28.5 (2004): 661-670.
  • Clifton, Peter M., Jennifer B. Keogh, and Manny Noakes. "Long-term effects of a high-protein weight-loss diet." The American journal of clinical nutrition 87.1 (2008): 23-29.
  • Dumesnil, Jean G., et al. "Effect of a low-glycaemic index–low-fat–high protein diet on the atherogenic metabolic risk profile of abdominally obese men." British Journal of Nutrition 86.05 (2001): 557-568.
  • World Health Organization, Food and Agriculture Organization of the United Nations, United Nations University. Protein and amino acid requirements in human nutrition: Report of a joint FAO/WHO/UNU expert consultation (WHO Technical Report Series 935). 2007.
  • Xu, Hong, et al. "Dietary fiber, kidney function, inflammation, and mortality risk." Clinical Journal of the American Society of Nephrology (2014): CJN-02260314.
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