By Shelby Stoner, PHASE IV Exercise Physiologist
Other articles in the Hormone Series:
Many of you probably know ghrelin as the “hunger hormone.” Ghrelin is a stomach derived hormone that acts to stimulate growth hormone (GH) secretion as well as affect various processes related to eating, body weight, and blood sugar regulation. It is primarily regulated by food intake, therefore ghrelin levels rise significantly before eating and when fasting, then go down for about three hours after eating with the timing of these rises being affected by our normal eating routine. Since ghrelin is thought to signal hunger to the brain once released from the stomach, you’d expect the body to increase ghrelin if an individual is undereating and decrease if they are overeating. Turns out, some studies have shown that ghrelin levels are naturally higher in children with anorexia nervosa and lower in those that are overweight and obese.
Alike other hormones, ghrelin has an impact on exercise metabolism and endurance as well as food intake post exercise. For most people, the benefits of exercise include weight management, appetite and blood sugar control, improved mental health, and better overall quality of life. Not only does ghrelin send hunger signals to the brain, it activates the release of growth hormone in order to help protect against dangerous drops in blood glucose as growth hormone is known to enhance fat metabolism. These functions of ghrelin is what led investigators to explore the role of ghrelin during exercise.
To do so, researchers took an inside look at the exercise metabolism of mice while performing high intensity exercise, comparing normal mice to those who were genetically engineered to lack ghrelin receptors. What the researchers found was that the mice who lacked ghrelin receptors, which are necessary for ghrelin activation, exhibited notably reduced exercise endurance when compared with normal mice. This finding suggested that ghrelin has the ability to boost exercise endurance, or the ability to exercise longer. The mice also ate significantly less food after high intensity training as compared to the normal mice, indicating that ghrelin affects food intake after exercise. “Our studies reveal that ghrelin is an important mediator of exercise endurance and appetite after exercise,” said Dr. Joel Elmquist, lead investigator.
Not only does ghrelin help boost exercise endurance and mediate appetite, there is some evidence that suggests that if you stick with the right kind of exercise, you may change how your body interacts with food. It’s more than a matter of just burning calories; exercise can also affect hormone regulation too. In general, exercise increases the production of ghrelin as workouts naturally make you hungry, in order to replace lost fuel stores. A 2012 study from the University of Wyoming looked at a group of women who either ran or walked and, on alternate days, sat quietly for an hour. After running, walking, or sitting, researchers drew blood to test for the levels of certain hormones and then directed the women to a room with a buffet. Human appetite is very complicated, driven by signals from the brain, gut, fat cells, glands, and even psyche. However, it’s hormones like ghrelin that stimulate hunger are known to be instrumental in determining how much we actually consume. As expected, the women who ran had elevated levels of ghrelin post exercise, which should have meant they would attack the buffet with gusto. But they didn’t. In fact, after running they consumed several hundred calories less than they had burned. Their restraint, the researchers concluded, was due to a concominant increase in other hormones that initiate satiety, or the feeling of being full. The augmented levels of satiety hormones “muted” the hunger messages from ghrelin.
Overall, the take home message from the study was that exercise “improves the body’s ability to judge the amount of calories consumed and to adjust for that afterward.” However, a major point to remember is that longevity counts. In order to see noticeable changes in weight, appetite control, and metabolic efficiency, you need to stick with the exercise program for several months.
Whether your goals are related to weight loss or improved performance, PHASE IV science has the answers. Call us to schedule a complimentary 30-minute health and fitness consultation at our facility in Santa Monica. 310-582-8212