Carbohydrates, glycogen, and training

Carbohydrate is the fuel clients argue about most, and the one training depends on most directly. Digestible carbohydrate is broken down to sugars, absorbed, and moved in the blood as glucose. Muscle and liver store glucose as glycogen. Those stores are what a hard session spends. A low store is why a client who “cut all carbs” can look flat and lose power in the second half of a workout even when they are still eating enough protein.

Keeping blood glucose in range

Glucose homeostasis is the body’s work of keeping blood glucose inside a range. Insulin moves glucose into tissues after a meal. Glucagon and other signals bring glucose back out of storage when it falls. Gluconeogenesis is the making of new glucose, largely in the liver, from non-carbohydrate sources such as certain amino acids. It is a normal pathway. It is not evidence that a client never needs to eat carbohydrate.

Ketosis is a state in which the liver makes ketone bodies because carbohydrate availability is low. It is a description of metabolism, not a recommendation. Some clients choose eating patterns that produce it. A fitness professional can explain the word. A fitness professional should not put a client into that pattern to treat a disease, and should send medical questions to a clinician.

Glycemic index is one column, not a verdict

Glycemic index ranks carbohydrate foods by how fast they raise blood glucose under test conditions, compared with a reference food. It is a real measurement and a poor shopping rule by itself. Portion size, the rest of the meal, and how the food was cooked all change the response. A baked potato and a potato chip do not become “good” or “bad” because of a single number. Use the index, if you use it, as one detail next to fiber, protein, and whether the meal supports the training session.

Insulin resistance means cells respond less well to insulin, so the body needs more of it to handle glucose. It is a clinical finding, not a label a trainer assigns from a client’s waist size. If a client has been told they have it, or has diabetes, their carbohydrate plan belongs with their clinician and a dietitian. You can still coach the training.

Fiber, alcohol, and sweeteners

Fiber is carbohydrate that human enzymes do not fully digest. It slows a meal, feeds gut bacteria, and is the part of “eat more plants” that has a mechanism you can explain. Alcohol is not a carbohydrate replacement. It provides calories, it is absorbed without a long digestion, and it impairs recovery and judgment. Sweeteners, both caloric and non-caloric, are a frequent client question. The honest answer is that a sweetener is not a food group. Replacing a large daily intake of sugar-sweetened drinks can matter. Adding a sweetener to an already adequate diet will not remodel a physique.

For the energy side of the same story, read calories and the energy nutrients. For fluid around training, read water and micronutrients.

These ideas are taught in more detail in The Science of Nutrition, a 5-hour continuing-education course for fitness professionals. To enroll, call customer service.