Effects of Repeat Exercise Under Different Prandial States and Diet Composition on Glucoregulation and Appetite.

Abstract

Glycemic responses to meal ingestion and exercise are important due to their relevance to type 2 diabetes. Studying the impact of a single exposure of exercise or meal on glucoregulation could not reveal the real life situation that meals are eaten, and exercise if necessary, more than once in a day. It requires a better understanding how exercise and meal interactions on glycemia through different prandial states from fasting, to early- then late-postprandial periods. Additional complexity is a circadian decline in glucose tolerance and insulin secretion in the afternoon/evening. This dissertation employs a repeat-event design, using two isocaloric meals and two bouts of moderate-intensity exercise to examine the effects of exercise performed in different prandial states on glucoregulation (Study 1), the influence of dietary composition in this process (Study 2), and the impact of satiating gut peptides, glucagon-like peptide-1 and peptide tyrosine tyrosine, associated with different prandial stages on exercise anorexia (Study 3). In Study 1, exercise significantly lowered blood glucose only when it was performed during late postprandial period, but not during early postprandial or fasting period. In Study 2, reducing carbohydrate content from 60% to 30% of energy intake reduced afternoon postprandial insulin response by 39% in parallel with a 48% reduction in glucose-dependent insulinotropic peptide. In Study 3, appetite suppression was associated with the late postprandial period regardless of the presence or absence of exercise. No consistent and specific association was seen between the two measured satiating gut peptides and exercise anorexia.

This dissertation provides scientific knowledge about the interactions between exercise and meals, including: (1) exercise performed during late postprandial period, but not other prandial states, leads to substantial declines in blood glucose concentration which could have negative impact on exercise performance but a positive impact in hyperglycemic insulin-resistant states; (2) reducing carbohydrate content of the meal to a half can reduce insulin response by 39% within a day, which could reduce the diabetogenic risk of postprandial insulin over-secretion; and (3) the repeat-event design of exercise and diet rather than the exclusive single-event design reveals the complexities of glucoregulation in the real life condition.