Three low-carb meals within 24 hours lowers post-meal insulin resistance by more than 30 percent, but high-carb meals sustain insulin resistance, a condition that leads to high blood pressure, prediabetes and diabetes, according to a University of Michigan study.

The study also found that two hours of moderate-intensity exercise, which is supposed to lower insulin resistance and blood sugar levels, has no impact on these results. To the contrary, blood sugar levels increase after the exercise, said Katarina Borer, professor in the School of Kinesiology and principal investigator in a study done with doctoral student Po-Ju Lin, now at the University of Rochester Medical Center.

Results
The third low-carbohydrate meal, but not the high-carbohydrate meal, reduced: (1) evening insulin AUC by 39% without exercise and by 31% after exercise; (2) GIP AUC by 48% without exercise and by 45% after exercise, and (3) evening insulin resistance by 37% without exercise and by 24% after exercise. Pre-meal exercise did not alter insulin-, GIP- and HOMA-IR- lowering effects of low-carbohydrate diet, but exacerbated evening hyperglycemia.
Conclusions
Evening postprandial insulin and GIP responses and insulin resistance declined by over 30% after three meals that limited daily carbohydrate intake to 30% compared to no such changes after three 60%-carbohydrate meals, an effect that was independent of pre-meal exercise. The parallel timing and magnitude of postprandial insulin and GIP changes suggest their dependence on a delayed intestinal adaptation to a low-carbohydrate diet. Pre-meal exercise exacerbated glucose intolerance with both diets most likely due to impairment of insulin signaling by pre-meal elevation of FFAs.

"What is remarkable about our findings is that they show that a simple dietary modification of reducing the carbohydrate content of the meals can, within a day, protect against development of insulin resistance and block the path toward development of prediabetes while sustained intake of high carbohydrate diets as shown in the two mentioned studies lead to increased fasting insulin secretion and resistance. And even more surprising and amazing is that exercise before the meals made the subjects more carbohydrate intolerant—that is, it increased evening blood sugar levels."

During exercise, you need energy, triggering hormones that promote the release of sugar from the liver. Most [of the body's] tissues become insulin-resistant to allow the brain and muscles to use that excess sugar," Borer explained. If the tissues don't use all that sugar for the workout, blood sugar will remain elevated, she added.
If you exercise after eating, however, "your meal provides the fuel" instead of your liver, Borer noted, and the excess sugar from your meal is likely used up. She recommended exercising within 40 minutes of eating.

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