For healthy and active individuals, adopting a diet high in protein can be key to achieving weight loss and athletic performance goals. Yet as the popularity for protein increases, people have raised questions about the overall safety of raised intakes over an extended period of time.
Now more scientific evidence is showing that high-protein diets are safe even with long-term use. In the first randomized-controlled trial to examine the effects of a high-protein diet over the course of a year, dietary intakes at three to four times greater than the current recommended daily allowance were found to be safe (1).
Long-term Study Details
In the study, 14 healthy resistance-trained men consumed their normal diet for a total of six months and alternated that with a higher-protein diet consisting of 3 grams per kilogram of body weight for six months.
For a 180-pound male, the amount of protein roughly equated to 250 grams of protein per day –about the same amount of protein found in nearly 10 servings (5 ounces) of roasted chicken. Because the protein intake was quite high, the study purposely used subjects who had several years of experience with resistance training because they’re representative of the type of individuals who might regularly consume these amounts.
The researchers reported that the higher-protein diet had no harmful effects on any measures of blood lipids, as well as kidney and liver function. They also wrote that the diet led to no increase in body fat, despite the increase in total calorie intake.
Each subject followed their own strength and conditioning program. However, the investigators were in regular contact with subjects to ensure that each completed a training log.
The extra protein consumed by each subject was obtained primarily from whey protein powder. Because of the common misconception that a high-protein diet corresponds with a low dietary intake of fiber, the researchers pointed out that the subjects also consumed approximately 30 grams of fiber per day.
Confusion Surrounding “High Protein” Intake
For this study, researchers defined “high” protein as exceeding 2 grams per kilogram of body weight They suggest that a high-protein diet should be defined according to the amount of protein consumed per unit of body weight.
One of the challenges in designing a study to evaluate the effects of high-protein diets is the current disagreement that exists in what constitutes a “high” protein intake. For example, the researchers explain that defining “high” in terms of percentage of calories can be misleading.
“If one were to consume a hypoenergetic diet [a reduced-calorie diet] of 1000 Kcal in which 35 percent of the calories were derive from protein, then that would amount to a paltry 87.5 grams of protein,” the researchers wrote.
For a 180-pound male, a 2 gram-per-kilogram intake translates to around 160 grams (or just over six servings of 5-ounce chicken breasts). Short-term studies have previously suggested no harm in protein at these higher levels along with potential of performance gains for athletes, but long-term data had been lacking (2-3).
The more recent research helps to fill the gap and suggests that protein at this level can be suitable for individuals so long as individuals are also eating foods containing nutrients such as carbohydrates, dietary fiber, essential fats, vitamins, and minerals.
- 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. 2016; 2016:9104792. Epub 2016 Oct 11.
- Campbell B, Kreider RB, Ziegenfuss T, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2007 Sep 26; 4:8.
- Tipton KD. Efficacy and consequences of very-high-protein diets for athletes and exercisers. Proc Nutr Soc. 2011 May; 70(2):205-14.