The impact of exercise on blood glucose and insulin levels
During exercise, insulin levels decrease, along with an increase in another hormone, called glucagon. This effect causes your liver to produce more glucose. As a result glucose levels can remain stable for about 2 hours of continuous exercise without any food intake. However during prolonged exercise of more than 60-90minutes, such as running, cycling or rowing, blood glucose levels tend to fall. There is some benefit in consuming carbohydrate (CHO) rich food during exercise to maintain blood glucose levels.
Repeated aerobic exercise increases insulin sensitivity and predisposes the individual with diabetes to hypoglycaemia (low blood glucose levels). The natural response during exercise is for insulin levels to drop. Therefore to mimic this natural response diabetics on medication may require an adjustment in medication as well. Hypoglycaemia can occur in people with diabetes who are taking insulin or certain oral medication.
Emphasis in the treatment of hypoglycaemia in response to exercise, is on medication reduction rather than increased carbohydrate intake from food.
It is really important that you speak to a dietitian and your doctor for personal advice especially if you are using insulin or other medication. You can find a dietician in your area by looking up ADSA (Association for Dietetics in South Africa).
The importance of carbohydrates
For optimum sports performance you need to consume a high carbohydrate diet, because carbohydrates produce the largest stores of muscle glycogen. (glycogen = carbohydrate that we eat is stored as glycogen in the muscles and liver). When you are running, your muscles rely on glucose and glycogen for energy. At lower exercise intensities your body can also use fat stores for energy, however the fat cannot provide the energy fast enough when you are exercising very hard. The larger your stores of glycogen and glucose the longer you can go before fatigue sets in.
Carbohydrate stores in the body are fully depleted within 2 – 3 hours of intense training. Your blood sugar levels will then drop and you become disorientated and weak (“hypo”). It is important to eat a diet rich in the right type of carbohydrates, not just before your event, but throughout your training program.
The GI and you
The rate at which glucose enters the bloodstream affects the insulin response to that food and this affects the fuels available to the exercising muscles. There is a place for both high and low GI foods in your diet to give you that competitive edge!
The recommended CHO intake for athletes with diabetes is no different from those for athletes without diabetes, assuming that blood glucose levels are well controlled between 4mmol/L and 8mmol/L. If blood glucose levels are either side of this range, food intake may need to be adjusted or exercise postponed. Speak to a health professional who can assist you on your journey to better glucose control.
It is important to monitor blood glucose levels frequently and adapt CHO intake on the basis of your own personal response. Therefore test your response on a regular basis during training, prior to the event. Get to know your own body well.
You might also want to read about how sleep can improve athletic performance.
