How important is the timing of exercise in affecting appetite hormones?
Ghrelin is the anorexic hormone that is responsible for regulating hunger. In particular, acylated ghrelin is one of the two isoforms of ghrelin that has the most effect on initiating appetite. When fasting, concentrations of acylated ghrelin increase, stimulating hunger and requiring the body to intake energy. Post meal, concentrations of acylated ghrelin decrease to reduce hunger. The initiation of fullness is mediated by two other hormones: pancreatic polypeptide (PP) and peptide tyrosine tyrosine (PYY). PP and PYY work vice versa to acylated ghrelin. Upon fasting, the concentrations of PP and PYY decrease, whereas upon meal ingestion, PP and PYY increase to stimulate fullness and signal meal termination.
In patients suffering from type 2 diabetes and obesity, these hormones are imbalanced. Type 2 diabetes patients have lower fasting acylated ghrelin concentrations and also a lessened decrease in ghrelin concentrations upon meal ingestion. Obese patients have lower PP and PYY concentrations post meal ingestion. However, studies have shown that acute sessions of aerobic exercise induce postprandial fullness in diabetic patients and increase postprandial PP concentrations in obese patients. Another form of exercise, resistance exercise (RE), is usually recommended for type 2 diabetic patients due to its favorable effects on lean body mass and glycemic control. However, the association of RE to appetite stimulating hormones is not clear. Nor is the association of the timing (pre-meal or post-meal) of RE to meal ingestion clear. Previous studies with RE on non-diabetic patients showed that during fasting, it reduced acylated ghrelin concentrations, increased PP concentrations, but did not affect PYY. In addition, another study showed that RE post meals in non-diabetic patients induced satiety due to the increase in PYY concentrations. Hence from the previous findings, the authors of this study hypothesized that RE would lower premeal ghrelin concentrations, decrease PP concentrations, but not effect PYY in type 2 diabetes patients. Furthermore, they hypothesized that postmeal RE would extend the appetite-suppressing effects compared to premeal RE, which would be due to the increase in PYY concentrations in type 2 diabetes patients.
The study consisted of 12 men and women with type 2 diabetes. All participants were obese, not requiring insulin, and undergoing standard medical care. The study required the subjects to report to the lab on specific days, eat standardized meals, and conduct either one of the following: 1) no resistance exercise (remained sedentary during testing period), premeal resistance exercise (45 minutes of RE 20-30 minutes prior to eating), or 3) postmeal resistance exercise (45 minutes of RE ~45 minutes after eating).
At the time point immediately before the meal, the perceived hunger was lower during the premeal RE, compared to no RE and postmeal RE (P < 0.01). The acylated ghrelin concentrations were also lower during the premeal RE trial, compared to no RE and postmeal RE trial (P = 0.03 and P 0.004, respectively). This data indicated that premeal RE increases perceived fullness and suppresses ghrelin concentrations before meals. At the time point after 240 minutes after meal, perceived hunger was lower in both RE trials (pre- and postmeal RE), compared to no RE- suggesting that RE extended the appetite-suppression effects of a meal.
PP and PYY concentrations were not significantly different between the trials. However, at the 60-min. postprandial time, PP concentrations were 22% and 34% lower during the postmeal RE trial, compared to no RE and premeal RE (P = 0.04 and P < 0.01, respectively). This data suggests that RE reduces PP concentrations pre- and post meals.
The study concluded that premeal RE reduced hunger and increased perceived fullness prior to eating, which was contributed by the decrease in ghrelin concentrations. Both pre-and postmeal RE reduced postprandial perceived hunger, but only postmeal RE increased postprandial perceived fullness. Proper control of diet and exercise plays a crucial role in maintaining blood glucose and weight balance. Regardless of pre- or postmeal, resistance exercise helps control hunger and satiety in patients suffering from type 2 diabetes.
- Premeal resistance exercise decreases hunger before eating.
- Premeal and postmeal RE’s reduce post-meal perceived hunger.
- Postmeal RE increases perceived satiety after meals.
Researched and prepared by Sabair Pradhan, Doctor of Pharmacy Candidate USF College of Pharmacy, reviewed by Dave Joffe, BSPharm, CDE
Timothy D. Heden; Ying Liu; Jill A. Kanaley. Impact of Exercise Timing on Appetite Regulation in Individuals With Type 2 Diabetes. Med Sci Sports Exerc. 2016;48(2):182-189