Race Fueling

Why the Type of Protein You Consume Can Make a Big Difference

The protein you choose can affect how you feel during and after exercise.

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It’s helpful to understand how protein is digested because it requires a good amount of time in the gastrointestinal tract and can therefore affect how you feel during and after exercise. If you eat a bowl of cottage cheese an hour before training, for example, you may experience stomach discomfort because during exercise, up to 85 percent of your blood travels to your muscles, while only a small amount stays in your stomach and liver. With fewer resources available for digestion, the process slows down, and it can give you a full or even painful feeling in your stomach.

Digestion of proteins begins in the stomach, where there is a highly acidic environment. Here, pepsin is secreted to begin the process. After this early digestive step, the nutrients move to the duodenum, where pancreatic secretions containing enzymes further digest the proteins. The digested proteins are divided into shorter segments, or peptides, and the enzymes here release a few amino acids. Next, the proteins are moved to the small intestine, where the exopeptidase enzymes begin to act. The digested proteins stimulate the formation of dipeptides and amino acids. This form of protein is taken to the liver. Then the amino acids are transported to all tissues so that the cells can conduct protein synthesis.

The breakdown and synthesis of amino acids occur in the body constantly, and the speed of this process is determined by both the source of protein and what’s going on in the body (see above). Hunger causes faster breakdown of proteins in the liver, and when protein synthesis activity in the muscles increases, protein digestion in the gut slows.

Republished from Sports Nutrition Handbook by Justyna and Krzysztof Mizera with permission of VeloPress.

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