Barbie Cervoni MS, RD, CDCES, CDN, is a registered dietitian and certified diabetes care and education specialist.
Jason DelCollo, DO, is board-certified in family medicine and on the faculty of Philadelphia College of Osteopathic Medicine.
People with diabetes are encouraged to exercise daily, which can improve blood sugar control, boost self-esteem, foster healthy habits, and elevate mood. But, for people with diabetes, exercise can affect blood sugar levels.
For athletes with diabetes, it is important to uncover how exercise affects blood sugar, as well as know what blood sugar levels are safe before, during, and after exercise and how to eat when exercising. This is especially important for parents of children with type 1 diabetes who are newly diagnosed or are too young to understand these difficult concepts.
This article will discuss the importance of exercise in diabetes management, how exercise affects blood sugar, and how to manage blood sugar based on the type of exercise you are doing.
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Type 1 diabetes is the most common form of diabetes in youth, but it can also affect adults. People with type 1 diabetes need to use manufactured insulin to keep their blood sugars in a healthy range.
Type 2 diabetes occurs when a person has elevated blood sugars, either due to impaired insulin sensitivity, insufficient insulin secretion, or a combination of both. Type 2 diabetes is more common in adults over age 45 but has increased in our youth over the past 20 years.
People with diabetes have difficulty using glucose (sugar) as fuel. This is either due to insulin deficiency, insulin resistance, or a combination of both.
Glucose is the body's preferred source of energy. It is a by-product of digestion and is found in foods with carbohydrates, like starches, fruits, vegetables, legumes, dairy products, sweets, and certain snack foods. After eating carbohydrates, blood sugars rise, and the pancreas secretes insulin. It removes glucose from the bloodstream by bringing glucose from the blood to the cells for energy.
When this system is functioning properly, the pancreas is able to produce insulin in conjunction with blood glucose. The pancreas will also produce a small amount of insulin throughout the day for normal bodily functions. In people with diabetes, particularly type 1 diabetes, their pancreas produces little to no insulin. Therefore, they need to take insulin to help keep blood sugars at goal. People with type 2 diabetes may need to take other glucose-lowering medication and/or insulin or non-insulin injectables to achieve the same result.
The effect exercise has on a person with diabetes will depend on the way that person responds to physical activity, as well as their fitness level, what their blood sugar was before starting exercise, how much medication they have taken, and what they have eaten. Certain types of exercise will lower blood sugar, while others can increase it.
There are times when people with diabetes should not exercise. This occurs when blood sugar is too low (hypoglycemia), too high (hyperglycemia), or if they have ketones.
Hypoglycemia is generally defined as a blood sugar <70 milligrams per deciliter (mg/dL), but people can feel symptoms of low blood sugar at different glucose levels. It's important for all people with diabetes to make sure that their blood sugar is at a safe level before exercising. Exercising when blood sugar is too low can cause blood sugar to drop even further, which can result in a hypoglycemic event. If blood sugar stays too low for too long it can result in coma and in rare cases death.
The American Diabetes Association (ADA) guidelines recommend that pre-exercise glucose should be 126–180 milligrams per deciliter (7.0–10.0 millimoles per liter (mmol/L)) but target levels should be individualized based on the type, intensity, and duration of activity. This recommendation can vary significantly based on the age of the child, their size, the type of exercise and duration, as well as their sensitivity to exercise.
Some people with diabetes need to take insulin before meals and snacks. Doses of insulin are matched to specific amounts of carbohydrates using an insulin-to-carbohydrate ratio. Decreasing the mealtime insulin before exercise and/or increasing food intake can help prevent and reduce the risk of hypoglycemia in people with type 1 diabetes.
Exercising when blood sugar is too high, may increase the risk of developing diabetic ketoacidosis (DKA), especially in those people with type 1 diabetes. Symptoms of high blood sugar include fatigue, increased thirst and hunger, and increased urination. If high blood sugar is due to insulin deficiency, the risk of DKA is higher.
For most people with diabetes, you should check for ketones if blood sugar is above 250 milligrams per deciliter for no real reason. If ketones are present, it is advised not to exercise. If ketones are not present, it may be okay to exercise, but you should always discuss this with your healthcare provider.
Although rare, people with type 2 diabetes can develop DKA. The American Diabetes Association does not recommend exercising when ketones are present.
Symptoms of ketoacidosis include thirst or very dry mouth, high levels of ketones, frequent urination, fruity odor or breath, dry skin, dehydration, decreased alertness, to name a few.
There is a great deal to consider as an athlete with diabetes, especially if you are taking insulin. You may have to reduce your insulin doses during or after exercise, but this will depend on the type of exercise you are doing, what you've eaten, the last time you took insulin, and how much you took. The best strategies will also depend on what you use for insulin delivery and how you monitor your blood sugar.
Other things athletes should ask themselves before a practice, training session, game, competition, or event:
Many people use a Continuous Glucose Monitor (CGM), also referred to as a sensor, that continuously checks the glucose in the interstitial fluid. They are especially beneficial during exercise because they have the capability of alerting a person when their blood sugar is too high or too low.
Athletes have unique nutrient requirements that are individualized based on their goals and type of activity. To keep blood sugars stable, people with diabetes need to have some combination of complex carbohydrates, fat, and protein. Sometimes a small snack may be necessary before the activity to prevent low blood sugars. In addition, a carbohydrate snack or meal after exercise of 30-60 grams of carbohydrate may be necessary to optimize performance.
Additional carbohydrate intake is recommended during and/or after exercise, depending on the duration and intensity of physical activity, to prevent hypoglycemia. For low- to moderate-intensity aerobic activities (30–60 minutes), and if the youth is fasting, 10–15 grams of carbohydrate may prevent hypoglycemia.
Small amounts of carbohydrates during an activity may be needed to keep blood sugars stable. Sometimes small sips of a diluted sports drink are recommended during exercise to prevent low blood sugar. Adequate hydration and frequent blood sugar testing are also recommended.
Exercise has positive effects on insulin sensitivity, weight management, social interaction, mood, the creation of healthful habits for adulthood, and more. Young people with prediabetes, type 1, and type 2 diabetes are encouraged to participate in at least 60 minutes of moderate to vigorous physical activity. This includes muscle and bone-strengthening activities at least three days per week.
Children with diabetes often express the need to fit in and "be like everyone else." Participating in exercise, both organized and unorganized, affords feelings of acceptance. Children can also make friends, have fun, develop confidence, and feelings of achievement. Exercise also promotes a healthy lifestyle and will allow kids to create habits that improve their overall health.
Parents play an instrumental role in providing a safe and encouraging environment for their children. If your child has diabetes, you might be nervous about having them participate in sports or gym, but physical activity is a way that children can engage, physically, socially, and emotionally.
Some things that can make this journey more successful and less stressful include:
People with diabetes can still be athletic and perform physical activity optimally with proper planning and management. If you have diabetes or are the caretaker of someone with diabetes, it's important to know how exercise affects blood sugar and what to do about it. Creating an individualized treatment plan with your medical team will help you manage blood sugars. You'll be educated on what your target blood sugars should be, types of foods to eat before, during, and after exercise, how to adjust medications, and how to prevent and treat high and low blood sugar.
Exercise is encouraged for all people with diabetes, regardless of the type. If you are a parent of a child with diabetes you may be worried about how athletics will impact their blood sugar. While exercise can increase or decrease blood sugar, there are many strategies to keep blood sugars within a safe range. Communicate your child's diagnosis with coaches, teachers, and instructors for safety. Your medical team is a resource to help you or your loved one stay safe and maximize performance.
Yes, people with diabetes can live active lives. There are many different types of professional athletes who have diabetes, both type 1 and type 2. Some professional athletes play basketball, baseball, tennis, football, swimming, etc.
Depending on what type of athletics you are participating in, diabetes can increase or decrease blood sugar, which can cause adverse symptoms, including lethargy, lack of concentration and focus, and more. Careful blood glucose monitoring, nutritional management, and prevention and treatment of low blood sugar will be important to optimize athletic performance.
Yes, exercise is good for people with type 1 diabetes. In fact, physical activity and exercise positively impact metabolic and psychological health.
American Diabetes Association Professional Practice Committee. 14. Children and Adolescents: Standards of Medical Care in Diabetes—2022. Diabetes Care. 2022;45 (Supplement_1):S208–S231.
Center for Disease Control. Type 2 diabetes.
American Diabetes Association. Hypoglycemia (low blood sugar).
American Diabetes Association. Diabetes and DKA (ketoacidosis).
Barbie Cervoni MS, RD, CDCES, CDN, is a registered dietitian and certified diabetes care and education specialist.
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