By Rob Thoburn

“Changing the macronutrient composition of an individual’s diet can result in weight loss despite the ingestion of the same amount of energy.”

Lambert, C.P.; Frank, .L.L; and Evans, J. (2004). Macronutrient considerations for the sport of bodybuilding. Sports Med. 35(5): 317. 

The inch defines a unit of length or height. The calorie defines a unit of energy—edible energy. That’s where the similarity between inches and calories ends. You see, whereas an inch is an inch, a calorie is not a calorie.

In fact, there are different forms of edible energy. The three most important are carbohydrate, protein and fat.

Dietary Carbohydrate, a.k.a. “Sugars and Starches”
That’s it in a nutshell: Dietary carbohydrates are sugars and starches. Because of their chemical makeup, they offer your body its most efficient means of obtaining glucose, a.k.a. blood sugar.

Many sugars contain at least one molecule of glucose. Starches consist of chains of glucose molecules linked together. When you eat either, your gut breaks them down, freeing the glucose so it can be absorbed into your bloodstream. That takes place at various rates, depending on the makeup of the carb. The faster that process occurs, the higher the glycemic index of the food. For instance, a bowl of soggy corn flakes has a high G.I., while a fresh grapefruit raises blood glucose levels much more slowly.

“The Glucose Economy”™
Glucose is your most important energy source, or fuel. Some tissues just can’t do without it. Your body does everything in its power to preserve its overall supply of glucose, something I refer to as the glucose economy. That includes making glucose from scratch and increasing the burning of fat, which spares the glucose economy.

Dietary Protein
Protein consists of chains of amino acids linked together. Your body chooses from an alphabet of more than 20 different amino acids to build its proteins. Examples include the hemoglobin in your red blood cells and the force-generating proteins inside your muscle cells. Your muscle cells store glucose in the form of branched chains, which is called glycogen. Muscle glycogen can play an important role in muscle growth in response to pumping iron. The bulk of muscle hypertrophy in those who lift weights, however, is usually attributed to an increase in protein content. Lifting weights stimulates the muscle cells to make more force-generating proteins, and that causes them to become bigger and stronger.

Still, you can’t overlook the importance of muscle glycogen for building muscle. Witness the tremendous effect that the practice of carb loading can have on a bodybuilder’s physique in the days leading up to a contest. Also, some scientists with whom I’ve corresponded suggest that suboptimal muscle glycogen levels may be associated with suboptimal rates of muscle protein synthesis, thereby hampering your ability to build muscle.