Protein and Endurance Athletes: Timing it Right
Will Brinks explains the many benefits of protein for endurance athletes.
Endurance athletes are all too familiar with the message that carbohydrates are the most important food to eat. Carbohydrates fuel muscles like petrol your car.
Muscle is comprised of many components: connective, nerves, blood capillaries, and muscle cells. All these have a common building block: proteins. There are thousands of proteins in your body with many different structures and functions. The building blocks for these proteins come from our diet.
Protein Turnover

Proteins in your body are continuously degraded and synthesized by processes that require energy. These processes are tightly linked to energy consumption by your whole body. Whole-body protein synthesis represents the combined synthesis rates by all the tissues and organs in your body.
Nutrition, aging, exercise and other factors can affect protein synthesis in individual tissues while having little effect in others. Accordingly, athletes are concerned with protein synthesis and degradation rate in muscle tissue. Yet how does endurance exercise affect muscle protein tunover?
Most short-duration exercise, such as sprinting and weightlifting, relies on carbohydrate for fuel. Glycogen, the stored form of carbohydrate in muscle tissue, and blood glucose provide the preferred substrate for chemical energy that fuels muscle power. Although fat and protein also supply fuel for muscles, glycogen is generally the most efficient fuel source for long-duration exercise.
During prolonged exercise, such as long-distance running or cycling, proteins can be broken down to provide 3 to 5% of the total energy expenditure. When muscle glycogen becomes low, or if initial glycogen stores are low, energy contribution from protein can be up to 10%.

One way to prevent the breakdown of muscle protein for fuel is to provide adequate carbohydrate. Many endurance athletes think that eating a lot of carbohydrates is enough to protect precious muscle protein. Indeed, insulin, the hormone secreted in response to ingesting carbohydrates, helps protect muscle from protein degradation. Still, insulin alone does not increase protein synthesis. Insulin combined with amino acids is optimal for a positive protein balance.
How Much Protein?
For many years the issue of daily protein intake requirements by athletes has been an ongoing controversy. The typical recommendation by most nutritionists corresponds with the Recommended Daily Allowance (RDA): 0.8 grams of protein per kilogram (0.36 g/lb) of body weight per day.
Because the typical athlete consumption is estimated at 0.7 to 1.6 grams per kilogram (0.3 to 0.7g/lb) per day, exercise physiologists generally do not consider protein supplementation for the average athlete justified. However, several studies suggest that athletes should consume more than the RDA depending on their training demands and overall diet. Several studies have determined that athletes performing low to moderate intensity endurance exercise maintain a nitrogen balance (an indicator that protein intake equals protein degradation) with a protein intake of 0.9 to 1.1 g/kg per day. On the other hand, to maintain nitrogen balance in elite endurance athletes, estimated protein requirements of 1.5 to 1.8 g/kg (0.7 to 0.8 g/lb) per day may be required.