Professor of the Practice of Law University of Denver Sturm College of Law

Sugar May Cripple Exercise Benefits

Strong aerobic fitness is associated with longevity.  Exercise is the best way to improve aerobic fitness. 

Scientists have discovered that eating sugar, simple carbs, and processed foods may make your workouts less effective.  Simple carbs include honey, high fructose corn syrup, and table sugar.

Researchers used diet and medicine to raise blood sugar in mice and then examine its impact on their exercise.  There were 3 mice groups: the control group on a regular diet, the group on a diet of high fat and sugar, and the group given a drug to lower their capacity to produce insulin and therefore control their blood sugar. 

After 4 months, the researchers tested the fitness levels of the mice.  First, they had the mice run on a treadmill to exhaustion.  Then they gave the mice running wheels for the next 6 weeks, allowing them to jog on the wheels at will.  All the mice ran about 300 miles in that 6-week period however, the fitness levels of the mice were not the same.  The control group mice could run longer on the treadmill before exhaustion, and they were more fit than the mice in the other 2 groups who suffered from high blood sugar.

When researchers examined the muscles of the mice, they found that the control group mice had grown healthy new muscle fibers with a network of new blood vessels that carried oxygen and fuel into them.  The high-sugar mice had muscles with new collagen deposits that blocked new blood vessels and prevented the muscles from adapting to exercise. 

Finally, the researchers studied 24 young adults and found that those with prediabetic blood sugar levels had the lowest endurance during treadmill testing and high activation of proteins in their muscles that can reduce improvements from aerobic exercise.

Takeaway: Diets high in sugar, fats, and processed foods are likely to reduce the positive fitness benefits of exercise.


Tara L. MacDonald, et al., Hyperglycaemia is Associated with Impaired Muscle Signaling and Aerobic Adaptation to Exercise, 2 Nature Metabolism 902-917 (2020),

Gretchen Reynolds, Is your Blood Sugar Undermining your Workouts?, New York Times, Feb 24, 2021,

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