How Sugar Sabotages Your Fitness
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How Sugar Sabotages Your Fitness

If you work out but your endurance doesn’t improve, your diet may be the culprit.

By Kellee Katagi

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We know too much sugar can cause health problems, but new research indicates it can affect your fitness, too.

In a recent study published in Nature Metabolism, researchers from the Joslin Diabetes Center in Boston looked first at rodents and then at humans and discovered that, for both, chronic high blood-sugar levels negated some of the positive effects of exercise, primarily aerobic endurance.

The research inspiration came from this fact: About 20 percent of the population doesn’t improve their aerobic capacity, even when they exercise. And that’s troubling. As the study asserts in its intro: “High exercise capacity has emerged as one of the best predictors of health and longevity in animals and humans, and strongly protects against mortality.”

In the rodent trial, scientists tested six groups of mice over six weeks—three groups were sedentary and three scampered on a running wheel. From there, they were further divided by diet, as follows:

  • One group from each camp ate a lot of sugar and saturated fat.
  • Another ate a regular diet but received an insulin blocker, hindering their ability to process sugar.
  • The third was a control group that continued their previous diet, which was about 75 carbohydrates but didn’t have refined sugar.

The Results

The good news is that across all categories, the running mice fared better than those that just sat around. They didn’t gain as much weight and they improved their overall metabolic response.

But for all their scampering, both the high-sugar and insulin-blocked crews failed to boost their aerobic endurance. So the scientists dug a little deeper. They found that, contrary to the control mice, both groups did in fact have chronic high blood sugar and that (in very layman’s terms about a complex, technical subject) their diet also changed their muscle structure on a cellular level and altered the muscle-signaling process—which ultimately meant that all their running didn’t boost their endurance. This occurred whether or not the mice gained weight.

The researchers’ subsequent study, involving 24 humans, also found a strong correlation between chronic high blood sugar and low aerobic fitness levels.

The Takeaways

Here’s what we can learn from our rodent friends and their human counterparts:

  • Exercise is better than no exercise, regardless of how you eat.
  • A diet high in sugar and saturated fats may sabotage not only your fitness levels but also your long-term health and longevity—even if you exercise.

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