Diets high in protein are popular in the bodybuilding, weight training and athletic communities. An enduring belief exists that protein = muscle, and therefore if you eat more protein you will pack on more muscle and strength. What's more likely is that there is a 'sweet spot' of protein intake. Below the magic number will mean that your diet is not optimum for your activity, and above the number means only that the extra protein has no additional anabolic or energetic value, other than as a vehicle for nutrients.
High-Protein Diets for Athletes and Bodybuilders
How is one to know what that sweet spot is and how much protein to take in? In a previous article on protein requirements the estimated intakes for various activities and sports are listed. Physical activity requires extra energy and stimulates appetite. That extra intake of food that goes with an increase in energy expenditure in exercise also helps to increase your protein intake. To some extent the system is self-regulating. You only need to ensure you balance that extra food consumption by including some protein. But in any case, a modest targeting of extra protein intake in the form of protein foods or shakes should do no harm. What's not useful is an obsessive concentration on protein intake to the point of consuming costly and usually unnecessary commercial protein supplements.
High-Protein Diets in Weight Loss
High-protein diets are not only popular with bodybuilders and the gym crowd, they also have their share of supporters in weight loss advocacy and advice. The general rationale goes like this.
1. Standard nutrition texts say that protein is known to take more metabolic energy to digest than fat or carbohydrate. The more protein we eat in place of fat or carbohydrate, the better it should be for weight loss purposes advocates say.
This is referred to as the thermogenic effect of food (TEF). The problem with promoting these early studies of protein TEF for weight loss is that when you actually calculate the differences in energy based on a modest increase in protein and a decrease in carbohydrate, the calorie equivalents tend to be trivial -- a few tens of calories a day. In addition, those early studies were unlikely to have compared wholegrain and high-fibre or low-GI carbohydrates with protein. Wholegrain carbohydrates have their own extra metabolic cost compared to refined carbs, so ultimately comparisons with protein will be inconsequential if, as recommended by most nutrition authorities, wholegrain, high-fiber and low-GI carbohydrates are consumed as a regular part of a weight-loss diet.
2. Protein is more satiating and keeps you feeling full for longer and you eat less, say the high-protein supporters.
As in the first point, studies that show the superiority of protein over carbohydrates for satiety have usually not compared protein with wholegrain / high-fibre carbohydrates. Again, the protein superiority in this regard is based on science that doesn't adequately compare reasonable alternatives. The weight loss advantages of high-protein diets in this context are likely to be inconsequential or at least trivial.
Even so, during weight loss with a reduced-energy diet, keeping protein intake steady while reducing other macronutrients (fat and carbohydrate), seems to help with the maintenance of muscle tissue during weight loss -- which is desirable. In percentage of energy terms this could be construed as a high-protein diet, but in protein per pound or kilogram of bodyweight, the protein intake is steady or even rises a little with fat loss.
Safety of High-Protein Diets
In healthy men and women, high-protein diets do not seem to impair kidney function over time. However, it is possible they may not be safe for people with chronic kidney disease.
High-protein diets, especially animal protein, have been associated with bone mineral loss and fractures in some long-term studies in women, but this effect is yet to be clearly proven. Also, low-protein diets are similarly associated with reduced bone mass.
Moderately high-protein diets in the absence of kidney disease and within a balanced, healthy eating regimen are unlikely to present any health risk, and may confer certain advantages. However, for athletes and heavy exercisers, the replacement of carbohydrate with excessive protein may not provide the energy substrate required for peak performance in some circumstances.
Sources
Efficacy and consequences of very-high-protein diets for athletes and exercisers. Tipton KD. Proc Nutr Soc. 2011 May;70(2):205-14.
Dietary fiber and weight regulation. Howarth NC, Saltzman E, Roberts SB. Nutr Rev. 2001 May;59(5):129-39.
Wholegrain vs. refined wheat bread and pasta. Effect on postprandial glycemia, appetite, and subsequent ad libitum energy intake in young healthy adults. Kristensen M, Jensen MG, Riboldi G, Petronio M, Bügel S, Toubro S, Tetens I, Astrup A. Appetite. 2010 Feb;54(1):163-9.
A high ratio of dietary animal to vegetable protein increases the rate of bone loss and the risk of fracture in postmenopausal women. Study of Osteoporotic Fractures Research Group. Sellmeyer DE, Stone KL, Sebastian A, Cummings SR. Am J Clin Nutr. 2001 Jan;73(1):118-22.
