Theories abound concerning the mechanisms that regulate food intake. Some sources indicate that the hypothalamus (the part of the brain that regulates appetite) closely monitors levels of certain nutrients in the blood. When these levels fall, the brain signals us to eat.

Scientists distinguish between hunger, an inborn physiological response to nutritional needs, and appetite, a learned response to food that is tied to an emotional or psychological craving and is often unrelated to nutritional need. In some instances, the problem with overconsumption may be more related to satiety than to appetite or hunger. People generally feel satiated, or full, when they have satisfied their nutritional needs and their stomach signals, “No more needed, thanks!” In overweight people, it is possible that the monitoring system does not work properly and the cues to eat are more frequent and intense.

Hormones
Some researchers are focusing on the hormones leptin and peptidYY, which scientists believe signal the brain when a person is full and needs to stop eating. It is believed that if we can enhance these levels in the blood, people may find it easier to control their hunger urges.

A hormone produced in the stomach—known as ghrelin—may be among the most important players in our collective difficulties in keeping weight off. Researchers at the University of Washington studied a group of overweight people who had lost weight over a six-month period. They noted that ghrelin levels rose before every meal and fell drastically shortly after every meal, suggesting that the hormone plays a role in appetite stimulation.

Exercise
Here’s where the Yes and No answers come in:
There are studies that suggest that exercise suppresses the appetite by affecting appetite hormones. While some research suggests that exercise stimulates hunger and food intake, most short-term studies (where hunger and food intake are evaluated right after the workout) do not find this to be true. In fact, vigorous exercise has been found to reduce hunger, although the effect is temporary and unlikely to have a long-term impact on overall food intake. A criticism of these types of studies is that hunger and food intake were not tracked for a long enough time period. In a study where participants were followed for up to 14 days, researchers found, on average, that 30% of the calories burned during exercise were compensated for. In other words, people increased their food intake by a small amount, but not nearly enough to cover the total calories burned during physical activity.

Emerging research suggests there may be a degree of individual variation in hunger in response to exercise. For example, in a 2009 study where participants followed a 12-week exercise program, participants that did not lose weight reported significant increases in total daily hunger compared with the participants who lost a significant amount of weight.

Behavioral reasons
Another cause for eating more in response to exercise may be due to behavioral reasons (“I worked out, so now I can have a bowl of chips”). Overestimating calories burned during exercise and underestimating food intake is a common occurrence. There are people who increase the amount of calories they eat after they start exercising as a sort of reward for working out. Some make high-calorie food choices based on the fact that they’ve burned off extra calories and feel entitled to a splurge. Unfortunately, the treat may end up being higher in calories than the calories that were burned off while exercising, resulting in a positive calorie balance.

According to a new study, a vigorous 60-minute workout on a treadmill affects the release of two key appetite hormones, ghrelin and peptide YY, while 90 minutes of weight lifting affects the level of only ghrelin. The research shows that aerobic exercise is better at suppressing appetite than nonaerobic exercise. This line of research may eventually lead to more effective ways to use exercise to help control weight. While the study showed that exercise suppresses appetite hormones, the next step is to establish whether this change actually causes the suppression of eating.

The bottom line is that there are many factors conspiring to affect our appetite and eating habits. Recognizing these factors and making conscious decisions to change lifestyle behaviors is an important step in maintaining a healthy weight.

 As seen in TOPS News, April-May 2011