Carbohydrate Metabolism Simplified

Carbohydrates are broken down into glucose, which fuels brain function and muscle contraction. Understanding carbohydrate metabolism provides insight into how different types of carbohydrates influence energy availability and metabolic processes.

Carbohydrate Digestion and Absorption

When carbohydrates are consumed, they are broken down by enzymes in the mouth, stomach, and small intestine. Complex carbohydrates (starches) require more enzymatic breakdown than simple sugars. The resulting glucose is absorbed into the bloodstream, raising blood glucose levels.

Glycemic Response and Insulin

The rate at which carbohydrates raise blood glucose varies. Refined carbohydrates and simple sugars typically produce rapid increases in blood glucose, triggering proportional insulin release. Carbohydrates with higher fibre content or lower glycemic index values produce more gradual glucose increases and smaller insulin responses. Individual responses to the same carbohydrate vary based on factors including meal composition, physical fitness, and metabolic state.

Glucose Storage and Utilisation

Excess glucose beyond immediate energy needs is stored as glycogen in the liver (approximately 100 grams) and muscles (approximately 400-500 grams depending on muscle mass). This glycogen provides rapidly accessible fuel during activity and between meals. When glycogen stores are depleted, the body increases fat oxidation and, under prolonged energy deficit, breaks down muscle protein for glucose production.

Carbohydrates and Physical Activity

During high-intensity exercise, carbohydrates serve as the primary fuel source. Carbohydrate availability influences exercise performance and recovery. After intense activity, carbohydrate consumption supports glycogen replenishment. During lower-intensity, longer-duration activity, fat oxidation comprises a greater proportion of total fuel use, though carbohydrates still contribute significantly.

Fibre and Satiety

Dietary fibre, a carbohydrate component that is not digestible, influences satiety independent of calorie content. Higher fibre intake produces fuller sensations earlier in meals and sustains satiety longer. Fibre also influences intestinal motility and the composition of the microbiome, with broader metabolic implications.

Important Context