To improve blood glucose levels, men who are overweight or obese may want to put off eating breakfast until after they have exercised. Regular exercise in a fasting state increases intramuscular and whole-body lipid use compared with eating before regular exercise, therefore improving insulin sensitivity, according to results from a study published in the Journal of Clinical Endocrinology & Metabolism.

The researchers aimed to determine whether exercise before or after breakfast was more effective for intramuscular lipid use and postprandial glucose metabolism. To study the effects of fasting on muscle lipid use, the researchers conducted 2 experiments: an acute, randomized, crossover design (Acute Study) and a 6-week, randomized controlled design (Training Study).They also examined whether the results were better with a carbohydrate-rich (Training Study) or a mixed-macronutrient (Acute Study) breakfast.

A total of 30 men who were overweight or obese and were self-reported nonexercisers participated in monitored moderate-intensity cycling. Men in the Acute Study had an average body mass index of 30.2 kg/m2,whereas men in the Training Study had an average body mass index of 30.9 kg/m2.

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In the Acute Study, results suggested that exercising before consuming breakfast resulted in a net increase in intramuscular lipid use of type I and type II fibers compared with exercising after breakfast. The plasma glucose area under concentration-time curve was 6.70 mmol/L with fasting vs 5.91 mmol/L with eating (P <.01), noted the researchers. Serum insulin AUC was also higher with fasting, at 86.9 mmol/L compared with 55.3 mmol/L after eating (P <.01)

Postprandial glycemia was not significantly affected by exercise before or after carbohydrate consumption among participants of the 6-week Training Study; however, exercise before carbohydrate consumption resulted in an approximately 2-fold higher lipid use (1666 kcal vs 799 kcal) and reduced postprandial insulinemia, which further increased oral glucose insulin sensitivity.

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“These data suggest that exercising in a fasted state can augment the adaptive response to exercise, without the need to increase the volume, intensity, or perception of effort of exercise,” the authors wrote.

“Experiments investigating exercise training and metabolic health should consider nutrient-exercise timing, and exercise performed before versus after nutrient intake (i.e., in the fasted state) may exert beneficial effects on lipid utilisation and reduce postprandial insulinemia.”


Edinburgh RM, Bradley HE, Abdullah N-F, et al. Lipid metabolism links nutrient-exercise timing to insulin sensitivity in men classified as overweight or obese [published online October 19, 2019]. J Clin Endocrinol Metab. doi:10.1210/clinem/dgz104

This article originally appeared on Clinical Advisor