If you have diabetes, you know that counting and cutting carbs is nothing new. But there’s such a thing as cutting carbs too much.
That’s especially true if you’re working out with diabetes — which you should, considering that exercise is a great way to naturally improve your body’s blood sugar control and insulin sensitivity, per a position statement from the American Diabetes Association published in November 2016 in Diabetes Care. After all, carbs provide essential energy to the body, and you can’t exercise, or at least not well, without them!
Even more important, if you don’t have enough carbs before and during your workouts, you put yourself at risk of hypoglycemia, or excessively low blood sugar. And the last thing you want is to faint when you’re under the bench-press bar.
Here, experts explain exactly how carbs can affect your workout performance and blood sugar, and how to approach both:
Why Your Body Craves Carbs When Working Out
“Carbs are an important source of fuel and provide the body with a quick burst of energy,” says Vandana Sheth, RDN, CDE, a spokesperson for the Academy of Nutrition and Dietetics. That’s significant even for sedentary activities — and why the National Academies of Science, Engineering, and Medicine recommends that adults consume 130 grams (g) of carbohydrates per day, spaced out between meals — but becomes increasingly meaningful when fueling yourself for exercise. This rule also applies to people with diabetes, whose carb recommendations need to be individualized but whose diets ought to include them all the same.
During exercise, the bulk of your body’s energy comes from carbohydrates, both those floating through your bloodstream in the form of blood glucose and those stored in your liver and muscles as glycogen, Sheth says. The longer and harder you work during any given workout, the more carbohydrates your organs and muscles need to stay energized, with research published in November 2013 in Sports Medicine showing that increasing carb intake can boost not only marathon performances but high-intensity intervals as well.
Whether you are looking to lose weight, build muscle, or improve your insulin and cardiovascular health, the more you can put into your workouts, the more you stand to get out of them.
How Your Blood Sugar Behaves During Exercise
When your body burns through carbohydrates for fuel during exercise, guess what happens? Your blood sugar drops.
If it drops too low, your workout isn’t the only thing that will suffer, warns Rachel Johnson, RD, a researcher specializing in diabetes nutrition at Abbott, who is based in Lake Bluff, Illinois. Signs of severe hypoglycemia include everything from shakiness and dizziness to rapid heartbeat and loss of consciousness.
The risk of low blood sugar during exercise is especially high in those people who take insulin or other diabetes-regulating medications, says Anthony Pick, MD, CDE, an endocrinologist at Northwestern Medicine Lake Forest Hospital in Lake Forest, Illinois.
In some individuals with diabetes, a spike in stress hormones, including adrenaline and cortisol, which naturally occurs during exercise, can cause blood sugar to rise rather than fall, he says. Potential consequences of experiencing an excessively high blood sugar level, called hyperglycemia, include headaches, nausea, and blurred vision. However, heightened blood sugar during exercise tends to be the exception, not the rule.
The Best Carb Strategy for Your Workouts
So how many carbs do you need before, during, and after exercise to maintain a healthy blood sugar level? Short answer: It depends.
Long answer: It depends on how long and hard you exercise, your current medications, and most important, your blood sugar level heading into your workout. “Just because you have diabetes, it does not automatically mean that you need additional carbs,” Sheth says. “It is important to check your blood sugar before and after your workout to determine the effect of your activity on your carbohydrate needs.”
According to the American Diabetes Association (ADA), it’s best to start your workouts with a blood sugar level between 90 and 250 milligrams per decileter (mg/dL). If your level is lower than 90 mg/dL, the organization recommends ingesting 15 to 30 g of fast-acting carbohydrates prior to the start of exercise, although the exact amount will depend on your body size and the workout you have planned. Larger bodies and longer, harder workouts require more fuel. Good preworkout snacks include a whole, tennis ball-size piece of fruit (think: apple, peach, or pear), rice cakes, white toast, or yogurt, Sheth says.
Meanwhile, if prior to exercise your blood sugar level measures at 250 mg/dL or more, it’s important to test for ketones, which are fat metabolites that indicate the body’s insulin level isn’t high enough to effectively control your blood sugar, according to the ADA. Consult your doctor on adjusting your insulin and do not exercise if you detect moderate to large amounts of ketones in your body.
Blood sugar testing shouldn’t stop once you start exercising. Aim to test your level every 30 to 60 minutes during exercise, and consider tweaking your carb intake as you go. You may need 10 to 20 g of carbohydrates for every 30 minutes of moderate exercise and anywhere from 5 to 10 g of carbs per 30 minutes for low-intensity cardiovascular exercise, Sheth says. She adds, “Those numbers can vary greatly per person, so use them as a guideline rather than a rule.” During exercise, consider getting any needed carbs from the same foods that you snacked on before your workout, or potentially from sports drinks and gels. However, it’s important to remember that these products are designed to quickly digest and absorb into the body, rapidly raising blood sugar, Sheth says.
Following exercise, test your blood sugar to determine the best postworkout snack or meal for you, Dr. Pick says. Then repeat testing every few hours. As your body recovers from exercise by shuttling carbohydrates into your liver and muscles, your blood sugar level may fall. In some people, exercise has a delayed effect on blood sugar, causing it to fall up to 12 to 16 hours following exercise, he says. It involves a bit of trial and error, but over time, it becomes a habit.
“Every person’s needs are so unique, so it’s important to work with your healthcare provider to determine a plan for you,” Johnson says. Get your medical team’s okay before beginning any exercise program, especially if you are new to exercise.
Discuss your workout of choice and ask for feedback on exercise and meal timing, the potential impact of medications on your blood sugar, and how you might need to adjust your medications as you become more active, Sheth says. A registered dietitian or certified diabetes educator, both of whom you can find through the Academy of Nutrition and Dietetics, can help you evaluate your unique needs so you can start your workout routine with confidence.
Written for Everyday Health