Abstract
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TO THE EDITOR: Dr. Chacko provides an interesting viewpoint on
the optimal time to exercise for glycemic control (1). While
intuitive to suggest that moderate-intensity exercise in the midpostprandial
state might best normalize blood glucose, other
factors warrant consideration. Patterns of exercise and its intensity,
along with diabetes classification, require individualized
attention because they differentially influence glucose/insulin levels
(2, 3) and underlying phenotype. Immediately after highintensity
interval exercise, blood glucose is reduced, independent
of whether it is performed before or after breakfast (4), an effect
that is greater in magnitude than with moderate-intensity exercise
(2, 4). As indicated (1), whether exercise timing matters for
chronic effects is unknown (notwithstanding the importance of
acute effects). Research is urgently needed to determine whether
acute exercise-induced responses translate to chronic adaptations
underlying improved insulin sensitivity and beta-cell function.
Some studies have examined exercising fasted vs. fed. Training
fasted or at higher intensities appears likely to elicit greater muscle
and whole body adaptations (5), including reduced lipid deposition
that impairs insulin signaling, and greater transcriptional
regulation of proteins involved in glucose disposal (i.e., GLUT-4,
AMPK). Further research is needed to determine the long-term
effects of fasted exercise on preventing and treating T2DM. Ultimately
the diversity of human physiology, disease progression (and
treatment) and individual behaviors (e.g., feeding pattern) complicates
a “one-size-fits-all” optimal exercise prescription. Also important
to consider are other risks (e.g., morning-impaired cardiovascular
control) balanced against the proven benefits of exercise and a need
to promote exercise compliance at the population level.