Stacy Sims

First, let’s talk about the role carbohydrates play in providing energy for working muscles, providing fuel for the central nervous system (CNS), enabling and perpetuating fat metabolism, and preventing the use of protein as a primary energy source. Remember, carbohydrates — specifically glucose — are the preferred source of energy for muscle contraction and biologic labor.

Glycogen, which is the term for glucose in its stored form, is limited in its ability to be stored: about 350 g in the muscles and 40 g to 50 g in the liver of a non-obese 70 kg man. The glycogen stored in a particular muscle is used directly by that muscle during exercise; glycogen cannot be “borrowed” from resting muscles. Hence, it is critical to restore glycogen levels in the muscles of the endurance athlete

The minimum daily intake of carbohydrates necessary for survival — that is, for supporting the CNS, red blood cell production, the immune system, and all tissues dependent on glucose — is ~130 g. You need considerably more than that to support any physical activity or exercise

The intensity and duration of an exercise period will directly affect the amount of glycogen that is used. It is common knowledge that low-intensity exercise (e.g. 20% to 30% maximal oxygen update [VO2 max]) uses minimal glycogen, but when the intensity of an exercise period approaches ~75% of VO2 max, the body’s storage of muscle glycogen will be almost completely depleted within 2 hours of cycling

Why is that? To put it succinctly: your diet can and should include some processed carbs as fuel during training, but the bulk of your carbohydrates should come from eating fruits, vegetables, and whole grains as part of your normal diet

Carbohydrates are made up of sugar molecules, which your body breaks down into fuel, especially when you are working hard. Sugars, starches, and fiber are all basic forms of carbohydrates. There are two main types of carbohydrates: simple and complex

Simple carbohydrates include table sugar, syrup, and glucose. Most of the time, these carbs should be avoided (exception: in training foods) and are conventionally recognized as “bad” carbs. You can also include candy, cake, beer, and cookies on this list

You see, your body treats complex and simple carbohydrates alike. It breaks them down into usable sugar energy to fuel your muscles and organs. It is not the type of carbohydrate that really matters; instead, it is how quickly your body can break it down and how much it will spike your blood glucose levels

The important thing to remember is that your body needs carbs, even if fad diets tell you otherwise. This becomes even more important if you are engaged in intense exercise. Without carbohydrates, your body will begin to break down your muscle tissue to fuel your body, which will sabotage your efforts

It is just as important to note that the health benefits of low-carb diets do not mean that they are strategically better for fat loss. Research published in The American Journal of Clinical Nutrition dropped a bomb when it compared a lower-carb diet to a higher-carb diet and discovered that each yielded no significant difference in rates of fat loss, metabolism, or lean mass retention