Protein intake is one of the most hotly debated topics related to sports nutrition. Most athletes probably ingest more protein than they really require and there is a flourishing market for protein supplements, amino acid mixes and all kinds of protein-based ‘power drinks’ that promise athletes top performance and massive gains of lean muscle mass.
The protein requirements of athletes are influenced by the following factors:
- How intensively the athlete exercises - the greater the exertion, the higher the protein requirement.
- How long the athlete exercises during training sessions and events - long periods of training will increase protein requirement.
- The type of exercise the athlete participates in - endurance training (e.g. body building, weight lifting) leads to protein breakdown and increases the requirement.
- The level of training the athlete has achieved - highly trained athletes have a lower protein requirement than athletes who are starting their training. During rest periods, increased protein synthesis occurs in highly trained athletes.
- The energy content of the diet - athletes such as dancers, gymnasts and light weight wrestlers who tend to restrict their energy intake to maintain a low body weight, as well as vegetarian athletes, may have a higher protein requirement and/or not ingest sufficient protein for their needs.
- Gender - male athletes tend to burn fat preferentially and thus usually require less protein than female athletes who tend to burn more protein and carbohydrates - despite this physiological difference most male athletes ingest large amounts of protein.
- The influence of hormones - the male hormone testosterone builds muscles, and insulin also has an anabolic effect that increases muscle growth. Cortisol, one of the stress hormones, is classed as a catabolic hormone which breaks down muscle tissue and increases the protein requirement.
So how much protein do athletes need?
The standard Recommended Daily Allowance (RDA) for protein in adult men and women is 70 g/day and 50 g/day respectively (which translates to about 1 g of protein per kg body weight per day). Experts working in the field of sports nutrition agree that the standard RDA for protein is too low for the requirements of most serious athletes.
Burke and Deakin (2000) list the following recommendations for protein intake by athletes:
Elite male endurance athletes – 1,6 g of protein per kg body weight per day
Athletes who exercise at moderate intensity – 1,2 g of protein per kg body weight per day (i.e. these are athletes who exercise about 4-5 times a week for 45 to 60 minutes)
Recreational endurance athletes – 0,80-1,0 g of protein per kg body weight per day
Rugby, football and other power sports – 1,4-1,7 g of protein per kg body weight per day
Resistance athletes during early training – 1,5-1,7 g of protein per kg body weight per day
Resistance athletes who have reached steady state – 1,0-1,2 g of protein per kg body weight per day
Athletes training at altitude – 2,2 g of protein per kg body weight per day
Female athletes - approximately 15% less protein than male athletes
To work out how much protein you need, do the following calculations:
Example 1: You are a male endurance athlete who weighs 70 kg, thus you require:
70 x 1,6 = 112 g of protein a day
Example 2: You are a resistance athlete (body builder or weight lifter) at the start of your training and you weigh 70 kg, thus you require:
70 x 1,7 = 119 g of protein a day,
but when you have reached steady state you will only require: 70 x 1,2 = 84 g of protein a day
Example 3: You are a female endurance athlete who weighs 50 kg, thus you require:
50 x 1,6 = 80 minus 15% (12 g) = 80 - 12 = 68 g of protein a day
Example 4: You are a male athlete who weighs 70 kg training at altitude, thus you require:
70 x 2,2 = 154 g of protein a day
Dangers associated with excessive protein intake
According to present-day experience, sports nutritionists believe that ingesting up to 2 g of protein per kg of body weight per day should not cause any negative effects in healthy athletes (those who do not suffer from raised blood fat levels or diabetes, or have kidney problems). Intakes exceeding this amount can, however, be potentially dangerous for the following reasons:
- High protein intakes are often associated with high intakes of animal fat (saturated fat and cholesterol), which can raise blood lipid levels and cause heart disease and certain types of cancer
- High-protein diets increase calcium excretion via the kidneys which can in turn lead to kidney stones and osteoporosis, particularly in female athletes who restrict their energy intake and suffer from amenorrhoea (absence of menstruation)
- Susceptible athletes may develop kidney disease if their protein intake is too high
- Research with animals indicates that a high protein intake may damage the liver
- (Dr I.V. van Heerden, DietDoc)