Up the Exercise Intensity to Burn Sugar as Fuel

Your body needs carbs to fuel many activities — from keeping your organs alive and performing daily tasks like walking your furry friend to boosting you through full-on workouts. But what about stored sugar, a carbohydrate we all know and love? Can you target your exercise regimen to burn sugar?

​Read more:​ Fat Burning Vs. Carbohydrate Burning

So, getting down to brass tacks: How much sugar should you be eating to begin with? According to the Centers for Disease Control and Prevention (CDC), your added sugar consumption should stay below 10 percent of your total calories each day.

When you consume sugar or carbohydrates (think fruits, veggies and grains), it's broken down into glucose, says Columbus, Ohio-based Kacie Vavrek, RD, LD, a sports medicine outpatient dietitian at the Ohio State University Wexner Medical Center. Some glucose goes directly to your blood sugar, while some is stored as glycogen as a backup energy source for later use.

When you eat too much sugar, the glucose that isn't immediately utilized by your body is stored as glycogen or fat.

But how can you use up that blood glucose before it gets stored away? There are then two ways blood sugar leaves your bloodstream and enters your cells for energy, says Dana Simpler, MD, a primary care practitioner at Mercy Medical Center in Baltimore, Maryland: "The first is when insulin connects to insulin receptors on our cells to allow blood glucose (sugar) to enter the cells," says Dr. Simpler.

The second is through exercise. "When exercising, our muscle cells can soak up blood glucose directly from the bloodstream without needing insulin," Dr. Simpler says. "Exercise is a great way to keep blood glucose from going too high, especially for [people with diabetes] or people with pre-diabetes."

If you regularly hit the gym or head out for a run, you might be wondering if there's a way to speed up the rate at which your body burns off stored sugar (glycogen). According to Dr. Simpler: Yes, exercise can be used to burn off sugar: Just turn up the heat.

According to a March 2018 review in ​Nutrients​, higher-intensity workouts rely more on carbohydrates than fat to fuel your exercise sessions. Translation? Your body prefers to use glycogen to power through a Tabata interval workout (aka work intervals that are twice as long as the recovery interval), and it prefers fat to push through steady-state cardio (aka a long 10-mile run).

While you're always burning calories from both carbohydrates and fat, Vavrek explains, lower intensity workouts burn a higher percentage of calories from fat versus carbohydrates or sugar. "During exercise, we tap into glycogen stores for energy to fuel physical activity," Vavrek says. However, she says, you'll also tap into fat stores for energy, especially when performing lower-intensity exercises because fat requires oxygen and takes longer to use as a fuel source.

HIIT, which stands for "high-intensity interval training," is just one of the ways you can burn sugar by performing short bursts of very intense exercise, followed by rest (thank you very much).

In a nutshell, the intensity at which you exercise determines the fuel stores you use to power through a workout. According to an April 2018 review published in ​Nutrition Reviews​, blood glucose and muscle glycogen are the primary fuels oxidized to produce energy when exercise intensity is greater than 60 percent maximal oxygen consumption (VO2max).

So, as your exercise intensity increases, you start to burn a higher percentage of calories from carbohydrates. Explains Vavrek, "High-intensity exercise is burning almost primarily carbohydrates for energy, as it is a very quick energy source that does not require oxygen."

And if you want to better fuel your workouts (and life!), the American Heart Association suggests hydrating and eating healthy carbs (think fruits and veggies, brown rice, whole-wheat toast) two hours before exercise. Then, rehydrate and refuel with protein-rich foods within 20 to 60 minutes after your workout to aid your muscles in repair and growth.

​Read more:​ How to Build the Best HIIT Workout for You