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Can High Blood Sugar Sabotage Your Workouts?

What's your blood sugar?
What's your blood sugar?

Two people who do the same cardio program, rarely get the same results. There are several things that determine how effective it's going to be.

Have you taken in enough water so you're properly hydrated? Did you eat foods that help your body recover when you finish? Are you getting enough sleep? What's the temperature you're running in and how hard are you pushing yourself? All these things can affect your results.

Now you can add something new to the list. If you have hyperglycemia, or higher-than-normal levels of blood sugar, your cardio workouts aren't going to be nearly as effective. In fact, you may not see many of the benefits that aerobic exercise provides.

Researchers from the Joslin Diabetes Center worked with three groups of mice. Two groups were given drugs or food to make the mice prediabetic and raise their blood sugar levels. The third group ate a normal diet of mouse chow.

All the mice were then allowed to run freely on an exercise wheel for six weeks. Every group ran about the same distance during the experiment, about 300 miles. In the end, all the mice had some metabolic benefits from their exercise.

But the two groups of mice with high blood sugar had a problem. They gained significantly less aerobic capacity over those six weeks of running. When researchers examined the mice muscles, the ones with high blood sugar had fewer aerobic adaptations, like new blood vessel growth.

Normal and High Blood Sugar Diagrams

Those high blood sugar mice mostly had new deposits of collagen. The collagen seems to have interfered with new blood vessel formation and hurt the muscles ability to adapt and grow from the exercise.

At the end of the experiment, the control group could run much longer before exhaustion than the two groups with high blood sugar.

It didn't matter if the mice had high blood sugar because they were obese from a poor diet or from the effects of insulin. Since both groups were affected equally, they were able to conclude the problem was a direct result of the higher blood sugar.

To find out more, the researchers turned their attention to people. They tested 24 young adults. None of the subjects had diabetes, but some did have elevated blood sugar levels.

Then they made everyone run on a treadmill. The subjects with the worst blood-sugar control had the lowest endurance. So the researchers examined everyone's muscle tissues to see what was going on.

It all came down to a molecule called c-Jun N-terminal kinase or JNK. After aerobic exercise, JNK was much more active in people with high blood sugar. The higher the blood sugar, the more active JNK signaling was. The job of JNK is to bulk muscle cells up with collagen rather than adapt to aerobic activity.

Everyone with higher blood sugar, was sending out signals to build collagen, rather than blood vessels that help you become more aerobically fit and live longer.

If you've got high blood sugar, it's important to get it under control. Dietary changes can amplify your workouts. Reduce your blood sugar and not only are you likely to lose weight, but you'll see quicker improvements from whatever your workout routine is.

That means reducing the amount of simple sugars and saturated fat in your diet while increasing the amount of fiber. In a typical day, most people should limit their sugar to no more than 40-60 grams. Men should try and get at least 30-40 grams of fiber and women should take in at least 25-35 grams daily.

Talk to your doctor about additional ways to get your blood sugar under control.

Diet and exercise are intimately linked. What you do with one can dramatically affect the other. Eating a healthier diet is good. Exercising is good. But if you do both, the combined results will be better than just doing one or the other.

What's your blood sugar?
What's your blood sugar?

Clinical Study: Nature Metabolism

Hyperglycaemia is associated with impaired muscle signalling and aerobic adaptation to exercise

Tara L. MacDonald, Pattarawan Pattamaprapanont, Prerana Pathak, Natalie Fernandez, Ellen C. Freitas, Samar Hafida, Joanna Mitri, Steven L. Britton, Lauren G. Koch & Sarah J. Lessard
Published: 20 July 2020


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