A study published in Appetite investigated the effect of glycemic index (GI) and fructose content in pre-exercise meals on appetite following moderate-intensity exercise. The study enrolled ten, healthy men with an average age of 21.7 years and average BMI of 20.9kg/m2. The three, isocaloric pre-exercise meals were classified as low GI breakfast without fructose (LGI), low-GI breakfast with fructose (LGIF), or high-GI breakfast without fructose (HGI). For the LGFI and HGI, approximately 25% of the diet was contributed by fructose or glucose, respectively. The calculated GIs for the LGI, LGIF, and HGI diets were 41, 39, and 72, respectively. All participants completed the three trials in a randomized, crossover design, with a minimum of seven days for a washout period. Participants were required to standardize their eating for 3 days prior to each trial. Each trial began with ingestion of one of the three breakfasts. Two hours after ingestion, participants were required to participate in 1 hour of moderate-intensity exercise. Following the bout of exercise, participants were monitored for a 1 hour recovery period. Appetite scores were assessed from sub-scores of desire to eat, hunger, fullness, and ability to eat. Other measurements collected include: venous blood draw (insulin), capillary blood draw (blood glucose), air sample, heart rate, rating of perceived exertion, rating of perceived thirst, and rating of abdominal discomfort.
Compared to the LGI and HGI trials, appetite scores were lowest for the LGIF trial at 30th and 60th minutes of the recovery phase. The postprandial blood glucose levels were highest in the HGI group at 15, 30, 45, and 60 minutes. Blood glucose was higher in the LGIF group compared to the LGI group at 30 and 45 minutes after meal consumption. Serum insulin concentrations were significantly higher for HGI than LGIF trials at 30 minutes after meal consumption. There were no differences in blood glucose during the recovery period. Post prandial blood lactate was higher in the LGIF trial than in the LGI and HGI trials. At the initiation of the recovery phase, blood lactate was higher in the HGI trial than in the LGI trial with no significant difference than the LGIF trial. Similarly, there were no differences between serum insulin levels during recovery.
Researchers conclude “that eating an LGIF breakfast resulted in decreased appetite scores compared with HGI breakfast and LGI breakfast. Lower glycemic and insulinemic responses were observed in the LGI and LGIF trial than in the HGI trial during the post prandial period…In conclusion, it appears that fructose content in, rather than the GI of, a pre-exercise breakfast meals affect subjective appetite score during the recovery period after 1-hr of brisk walking.”