How high blood sugar can work against your exercise goals

Role of high blood sugar on exercise

When performing aerobic (cardiovascular) exercise, such as running, swimming or cycling, you expect to feel fitter over time. However, not everybody is rewarded with better fitness. Probably 1 in 5 might feel as if their body is almost resistant to a training effect.

Based on epidemiological studies there was already some indication that consistently high blood sugar concentrations are related to a low exercise capacity. However, it was unknown how much blood sugar and aerobic fitness affect each other or whether a high blood sugar level results in poor fitness or vice versa. MacDonald and coworkers addressed this topic in a range of animal and human studies. They confirmed in a mouse model that high blood sugar levels diminish a training effect. In addition, structural changes of the skeletal muscle were identified in animals with chronically increased blood sugar levels and these structural changes were confirmed in humans. High blood sugar causes an accumulation of a substance called extra-cellular matrix (a component of connective tissue in which cells are embedded) including an increase in collagen content in the skeletal muscle. In addition, glucose binds to the extracellular matrix leading to increased stiffness. These structural changes seem to function as a barrier and cause mechanical stress during muscle contraction. Subsequently a number of reactions are initiated that are usually known for resistance exercise (like strength training or weight lifting), but not for moderate aerobic exercise.

Initially these observations might sound discouraging, however exercise-related benefits were also identified, namely reduced body weight and improved metabolic health including a lower and more balanced blood glucose. In time a reduction in blood glucose can help to lessen the barriers (extracellular matrix) in skeletal muscle that prevent the improvement in fitness. Thus with discipline and a good combination of exercise and a healthy diet to keep the blood sugar stable, improvements in endurance can be achieved. Isomaltulose is a sugar that can help to keep the blood sugar low and stable and therefore fits perfectly in a health-conscious lifestyle.

MacDonald et al. (2020) Nat Metab 125:110657.