The exercise and appetite link

What’s the first thing you do after exercising, other than take a shower? Eat – and often more than you planned to. Jennifer Kang explores whether a post-workout snack may be standing between you and your dream dress size

Photolibrary/Istockphoto   Whether we want to reward ourselves, allow ourselves to consume the calories we’ve lost without feeling guilty, or more simply, satisfy a hungry appetite, many of us find ourselves eating more and feeling hungrier after exercise. But when weight loss wisdom cautions us to avoid consuming food with calories in excess of calories burned, you can’t help but wonder whether post-workout binges, during which we often eat more than we normally would, are contributing to our expanding waistlines. Despite more gym memberships sold and a greater effort to engage in regular workouts in recent years, it seems they’re not having much of an effect on our nation’s collective weight loss – more than half of Australian adults are either overweight or obese, according to the Australian Bureau of Statistics. This raises the question: is our appetite, particularly our post-workout appetite, negating the effects of exercise? According to research conducted by Murdoch University, it could be. Here we check in with the experts to investigate what causes hunger, how a post-workout appetite can hamper your weight loss efforts and that questionable claim held by some workout enthusiasts that exercise can suppress our appetites.  Hello hunger Contrary to common belief, the desire to devour the calories we’ve lost during a workout (and more!) is not as simple as saying that over-eating post-exercise is caused by a greedy stomach or our body’s so-called ‘fat cells’ being resistant to slimming down. Whether in response to exercise or not, the feeling of hunger is our body’s natural reaction to compensate for depleted energy levels. An increase in hunger leads us to eat, which can subsequently negate the weight loss effect of exercise, making weight loss a difficult prospect. Ultimately, it is this internal compensation which results in most women failing in their weight loss aspirations when exercise alone is relied on. Researcher Dr Timothy Fairchild of Murdoch University is conducting a three-year project investigating the relationship between exercise and hunger and whether there is any way the relationship can be severed.  “When you exercise more, you deplete your energy stores and in response, your body sends hunger signals up to your brain,” he says. “If at the same time you are also reducing how much you eat, these signals are amplified, which then amplifies your hunger. “It then comes down to your desire to lose weight or ‘how bad you want it’; someone who has a very strong innate desire to lose weight may be able to suppress these signals, whereas someone less committed may end up failing at step one.” No-effect exercise Awareness of the relationship between exercise and hunger, and its potential to stifle weight loss, is not new. An American study published in PLoS One involved 464 overweight post-menopausal women, who didn’t regularly exercise, being assigned into four groups. Women in three of the groups were asked to exercise with a PT for varying periods of time per week. The control group were directed to continue their usual physical activity routines. All of the participants were asked not to change their dietary habits throughout the study. While all groups, on average, lost weight, the women who exercised with a PT did not lose significantly more weight than the control subjects and some women in the training groups even gained weight.  “This is actually a typical finding in a lot of these studies and something that has surprised many researchers,” Dr Fairchild says. Researchers found the desire to compensate for the energy lost during exercise hampered the effects of exercise on weight loss. Whether it was because the women wanted to reward themselves, or because they were hungry, exercise alone was not found to have been conducive to marked weight loss achievements. Some of us may have encountered this in our own pursuits of optimal health and fitness – you might be running an hour each day, thinking exercise alone will have weight loss effects, but you’re not losing any weight.  Dr Fairchild says any amount of calories consumed in excess of what the body burns will contribute to weight gain. So, if you consume 400 calories more per day then you burn, you will store those additional 400 calories. This is irrespective of whether the energy is consumed immediately after exercise or a few hours after exercise, Dr Fairchild explains. He says while it is known that multiple small meals raise our metabolic rate, which increases our capacity to burn calories, this strategy has not been found to work for everyone, since many people simply eat more food, more often. “Therefore, with respect to weight loss, timing of meals with respect to the exercise bout does not seem to play a large role, as far as we know,” Dr Fairchild says.   The hormonal hunger surge While we know exessive eating can neutralise the effect of energy-burning pursuits, according to Dr Fairchild, little is known about the actual connection that exists between exercise and hunger specifically, and how exercise can be manipulated to affect appetite. Dr Fairchild is researching the hormones that control hunger, including ghrelin, which stimulates appetite, and hormones such as leptin, insulin and peptide-YY, which suppress appetite, and says he will be looking at what happens to them during and after exercise. What is known among the scientific community is that when the body’s energy stores are empty or low, certain hormones are released in the body, alerting the brain so that stores can be replenished.  When the stomach is empty, it releases the hormone ghrelin, which is the primary hormone for stimulating appetite. On the other hand, when food is eaten, certain cells in the intestines release appetite-suppressing hormones. Dr Fairchild says it’s the quantity of these hormones and how we act on the information that reaches the brain that matter. “All these hormones and signals come to an area in the brain, which integrates this information and makes an interpretation – so when ghrelin is high, and all the appetite-suppressing signals are low, this can cause hunger,” he says. “However, it is how the person acts on that information that really counts. Some people may be able to simply ignore those physiological appetite signals better than other people.”  Goodbye hunger It’s no secret many of us get hungry after exercise, so is there any merit to findings that exercise actually suppresses hunger? Dr Fairchild says there is. With studies such as a research paper published in the American Journal of Physiology finding that certain types of exercise such as aerobic exercise suppress hunger, it might seem there is conflicting information. According to Dr Fairchild, however, two things need to be considered. First, the study revealed hunger suppression only occurred during exercise and the next one to two hours after exercise. Second, the study did not measure energy intake. “So, the findings are not based on how much people actually ate, but rather, gave each person a standard meal and then asked them how hungry they felt afterwards,” he says. “The exercisers in the study were not hungry while they were performing the exercise, and then for a short period thereafter. But, this difference does disappear and the people then typically become hungry.”  Make the most of it While the Murdoch University study is being undertaken over three years, research conducted so far, in collaboration with the University of Western Australia, has found that although food intake immediately after exercise was higher than normal, this did not account for the increased number of calories expended during exercise. “In other words, if volunteers expended an additional 500 calories through the exercise session, they did not eat an additional 500 calories more,” Dr Fairchild says. He hopes the research will reveal specific mechanisms where we can trick the body into thinking that energy stores are full, despite having completed a one-hour exercise session. In the meantime, it seems you’ll have to control your post-exercise portion sizes, the type of food you consume and your mindset to get the most weight loss benefits from exercise.