7.4.2: Carbohydrates: The Preferred Fuel

Carbohydrates are the body’s primary fuel source for high-intensity exercise. When you eat carbs, your body breaks them down into glucose, which is either used immediately for energy or stored in the muscles and liver as glycogen. During resistance training, your muscles draw heavily on glycogen stores to power the anaerobic glycolytic pathway—the energy system that fuels sets lasting roughly 30 seconds to 2 minutes (i.e., most working sets).

Simple vs. Complex carbohydrates: Simple carbs (sugar, fruit juice, white bread) are digested quickly and raise blood sugar rapidly. Complex carbs (oats, rice, potatoes, whole grains) are digested more slowly and provide sustained energy. In practice, the distinction matters less than most people think when carbs are consumed as part of a mixed meal containing protein, fat, and fiber—the other nutrients slow digestion regardless.

The glycemic index (GI) ranks foods by how quickly they raise blood sugar. While GI has academic value, it is largely irrelevant for people eating mixed meals. A baked potato has a high GI in isolation, but add chicken, vegetables, and olive oil and the glycemic response is dramatically blunted.

Carbs are not inherently fattening. Carbohydrates do not make you fat any more than protein or fat does. A caloric surplus makes you fat. Carbs are simply the most flexible macronutrient—once protein and fat minimums are met, the remaining calories can be filled with carbohydrates based on preference, performance needs, and activity level.

Carbohydrates are the “fill the rest” macro. Set your protein, set your minimum fat, and use carbs to reach your calorie target. Adjust up on heavy training days if you feel flat, and adjust down on rest days if you prefer.