What is the relationship between carbohydrates and exercise?

The study investigated the relationship between exercise intensity and carbohydrate requirements to maintain normal blood sugar levels. The study concluded that the relationship is not linear, because no glucose is required at high intensity exercise.

Regular exercise has many health benefits. However, people with diabetes may not exercise as much as they should because they are worried about their blood sugar levels dropping very low. One way to avoid this is to eat extra carbohydrate before, during or after exercise. Carbohydrates are an important source of energy. The body turns carbohydrates into sugar.

Although it is recommended that carbohydrates should be taken to prevent low blood sugar levels during exercise, not much is known about varying exercise intensity and carbohydrate requirements, especially in patients treated with basal insulin (long-acting insulin that keeps blood sugar levels stable).

The current study looked at the relationship between exercise intensity and the amount of carbohydrate needed to maintain normal blood sugar levels.  The study included 9 patients with type 1 diabetes. All participants completed up to 40 minutes of exercise at four different exercise intensities (low, moderate, moderate-high and high intensity), on 4 separate days.  Participant’s blood sugar levels were measured every 5 minutes. They were maintained at normal blood sugar levels during exercise and 2 hours afterwards by injections of glucose (sugar) and insulin.

The amount of carbohydrate that was needed to maintain normal blood sugar levels increased with an increase in exercise intensity, up to a moderate-high intensity. On average, participants needed 4.1g of carbohydrate in the form of glucose per hour at a moderate-high exercise intensity. The amount of carbohydrate needed did not increase, however, as exercise intensity increased. No glucose was needed at the highest exercise intensity.

This study concluded that the amount of carbohydrate needed to maintain normal blood sugar levels does not necessarily correlate with exercise intensity. Glucose was required during low to moderately high intensity exercise, but not at the highest intensity of exercise. 

In this study the participants were given glucose as an injection into a vein through the skin. However, in a real life situation individuals would take carbohydrate orally (e.g. by eating bread) and then the body would convert this carbohydrate into glucose.

Talk to your doctor about what measures to take to control your blood sugar levels during intense exercise.