It's true that bodybuilders and weight lifters need to keep the protein up in their diet in order to maintain and build the large muscle mass which is so important to their sports or recreation.
Protein, as most know, is found in meat, fish, chicken, beans, milk, in soy products like tofu and in lesser amounts in nuts and grains.
The estimated daily requirements are set by various nutrition authorities in each country. In the US, the Department of Agriculture (USDA) sets the guidelines for nutrients like protein as well as other major vitamins and minerals. For most people of average weight, the protein intake is set at less than 70 grams each day.
Athletes may require quite a bit more than this to support muscle repair, increased growth and to protect against the general hardships of vigorous training and competing. Yet sports nutrition authorities generally recommend no more than about twice the daily recommended allowance applicable to less active people.
Excess Protein is Not Required
Some bodybuilders and weight training athletes have taken this recommendation for extra protein to extraordinary limits and well beyond any scientific recommendation. While excessive protein seems to do no harm in healthy, active people up to a point, the risk may be more substantial for someone with kidney disease -- the overweight or diabetic for example.
Excess protein beyond the requirements of the body is broken down from amino acids into ketones or glucose or energy cycle intermediates for energy, and some is converted to ammonia then urea and excreted.
The situation is encouraged by the extraordinary vigor of the powdered protein supplement industry in the weight training and bodybuilding markets. Skim milk powder can supply all the extra protein required -- and at a fraction of the price of some expensive supplement brands.
I'll take you through an example to demonstrate the dynamics of protein requirements for weight training.
Three Ways of Nominating Protein Requirements
It's possible to suggest a protein intake based on three ways to calculate possible requirements.
- Quantity per pound or kilogram of body weight per day.
- Macronutrient percentages, for example a diet of 25% protein.
- Absolute amount of protein per day, 160 grams for example.
Protein by body weight. While the protein requirements for adult males are less than one gram per kilogram of body weight per day, estimates for athletes based on studies that evaluate nitrogen balance, a product of protein breakdown, suggest that up to 2.5 grams/kilogram/day may be required in exceptional circumstances. However, 2.0 grams/kilogram is used by many sports nutritionists as an upper ceiling of protein intake for athletes, weight trainers in particular. (Divide by 2.2 to get protein in grams/pound body weight/day.) Much less than this is going to be sufficient for moderate or less intense exercise.
Protein by macronutrient percentage. The macronutrients are carbohydrate, fat and protein -- essential elements in human nutrition. Government Dietary Reference Intakes (DRI) nominate an upper level of protein intake at 35 percent of total energy. For example, a 100 kilogram bodybuilder eating about 2 grams/protein/kilogram/day would eat 200 grams of protein each day. Even in a diet of 4000 calories per day -- not unusual for heavy training -- this diet is only 20 percent protein. 200 grams of protein is equivalent to about 600 grams of chicken or six grilled chicken breasts. Please note the 200 grams refers to pure protein and not the weight of whole food.
So in this sense, moderately higher protein intakes do not exceed government healthy eating guidelines.
Protein by daily intake. Considering that the US Dietary Reference Intake for an adult male of 100 kilograms is 80 grams/day (0.8X100), you can see that 2 grams/kilogram/body weight/day for 200 grams total is substantially higher. Women require slightly less, yet slightly more during pregnancy. Even though the standard dietary reference intakes are calculated to meet the requirements of 98 percent of the population in a particular group, athletes need more per kilo of body weight than sedentary people.
Extreme Protein Recommendations for Bodybuilding
A few bodybuilding and weight training coaches recommend protein intakes of 40 percent of energy; for example 40% protein, 40% carbohydrate; 20% fat. Let's take a look at this. In the 4000 calorie diet of our 100 kilogram bodybuilder, 40% protein would be 1600 calories, equivalent to 400 grams of protein at 4 calories per gram. That's 4 grams/protein/kilogram body weight/day; over four times the RDI and twice what's scientifically defensible. Not good.
Fast and Slow Proteins
How quickly amino acids get transported to blood and how quickly they then get assimilated into muscle and other tissue for repair and rebuilding is the basis of this idea. According to some enthusiasts, fast proteins such as whey are superior to slow proteins like casein. Both are derivatives of milk products. Here are some values (Bilsborough 2006):
- Egg protein 1.3 grams/hour
- Casein isolate - 6.1 grams/hour
- Whey isolate - 8-10 grams/hour
There's not much evidence that these variations make a difference to muscle building over the longer term, although whey has shown some advantage in short-term studies.
Yet the other useful information that can be gleaned from the numbers above is that with an average protein absorption of, say, 7 grams/hour, a theoretical absorption is limited to around 168 grams each day (24x7). If accurate, it makes the 400 gram/day protein diets look entirely unnecessary at best.
Safety of High-Protein Diets
Very high-protein diets may not be safe over time for the following reasons:
- High levels of nitrogen and amino acids can be toxic.
- High-protein diets are not safe for those people suffering from chronic kidney disease. Up to 20 percent of the population may be undiagnosed.
Lambert CP, Frank LL, Evans WJ. Macronutrient considerations for the sport of bodybuilding. Sports Med. 2004;34(5):317-27. Review.
Bilsborough S, Mann N. A review of issues of dietary protein intake in humans. Int J Sport Nutr Exerc Metab. 2006 Apr;16(2):129-52. Review.