Insulin and exercise: A delicate balance

This study examined the effect of reduced insulin doses before and after intense exercise on post-exercise glucose (sugar), insulin, and inflammation levels in type 1 diabetes patients.

Exercise is important for a healthy lifestyle. It can help maintain weight, increase cardiovascular fitness and reduce daily insulin (the hormone needed to break down glucose from food for energy) requirements in type 1 diabetes patients. However, it can also decrease blood glucose levels, leading to an increased risk of hypoglycemia (dangerously low blood glucose levels). To reduce this risk, it is recommended that patients reduce their dose of fast-acting insulin prior to exercise.

It has also been suggested that the dose of insulin given with a post-exercise meal also be reduced. It is possible that reducing both the before- and after-exercise insulin doses could lead to hyperglycemia (high blood glucose levels). It is also possible that it could increase the production of ketones (substances produced by the body as an energy source when there is no insulin to break down glucose), as well as inflammation (one way the immune system protects the body).

The current study examined whether reducing before- and after-exercise insulin doses increased rates of hypoglycemia, hyperglycemia, ketone production, and inflammation. Eight male type 1 diabetes patients took part in the study. Each patient completed two sessions. In both sessions, patients ran on a treadmill for 45 minutes. Before running, patients ate a meal and were given a dose of insulin 75% less than normal. Following the exercise, a second meal was eaten. During one session, patients received a full dose of insulin with the second meal. During the other session, the insulin dose was 50% less than normal. Throughout both sessions, blood glucose and insulin levels were measured, as were blood markers for inflammation and ketones. Patients were observed for 3 hours following the second meal.

Glucose and insulin levels were similar for the full dose and 50% dose through 60 minutes after exercise. Insulin levels peaked at 60 minutes for both groups, but peaked at a higher level in the patients who received the full dose (199 pmol/l^-1) compared to the 50% dose (109 pmol/l^-1). After 60 minutes, insulin levels remained significantly higher in patients in the full dose group. Glucose levels were lower in the full dose group compared to the 50% dose group.

63% of patients who received the full dose experienced hypoglycemia, compared to none of the patients in the 50% dose group. 37.5% of patients in the full dose group experienced hyperglycemia compared to 75% of  the 50% dose group.

No effect of post-exercise insulin dose was found on ketone production or inflammation.

This study concluded that reducing both before- and after-exercise doses of insulin does not increase ketone production or inflammation, but may increase hyperglycemia.

This was a very small study, and all participants were men who exercised regularly. A larger study, including both men and women, should be done to determine whether the results can be generalized to a larger population.

Discuss your before- and after-exercise insulin requirements with your physician before starting or increasing the intensity of any exercise program.