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Can't Slim Even If You Exercise?
Change Your Diet Through Your Appetite

Hiroshi Kawano
Assistant Professor, Faculty of Sport Sciences, Waseda University


In the days when humans lived by hunting, the amount by which they could reduce their energy consumption was important. Such circumstances account for the large part of human history. Consequently, we can speculate that people whose genetic constitution made them more economical, like fuel-efficient cars, were more likely to survive longer and that the human race has therefore become increasingly energy-efficient. In recent decades, however, developed countries have entered an era of food abundance, resulting in the emergence of problems with obesity due to overeating. Because of this, obesity prevention and reduction have now become necessary through exercise therapy and diet therapy. However, most people would still prefer to eat tasty food and lead an easy life. The fact is that controlling appetite is very difficult. If we can unravel the relationship between exercise and appetite, we may find it to be extremely natural. Although many people hope to lose weight or slim down by exercising, exercise does not produce results for everyone, unfortunately. So why can't everyone slim through exercise? It would be very interesting to know what kind of exercise can reduce appetite and let people slim effectively.

People who lose weight easily and people who do not

Increases and decreases in body weight are determined by the balance of energy consumption and energy intake. Accordingly, weight loss can be achieved by increasing energy consumption or reducing energy intake. However, some people who try to slim by increasing their energy consumption through exercise learn by experience that exercising does not help them to lose weight. In his talk last year at the Global COE Program's "Sport Sciences Creating Active Lives" international symposium, Professor Neil King of Queensland University of Technology in Australia announced that people unable to lose weight through exercise had bigger appetites than those who could lose weight. We can assume that in people who cannot lose weight through exercise, the energy they consume by exercising is offset by the food they eat. In other words, they have chronic appetite stimulation. Professor King's research group also announced that a 12-week exercise program increased levels of a hormone called ghrelin which simulates appetite. In this way, people have a homeostatic function that kicks in to compensate for energy lost by the body after performing regular exercise. The better this function works, the harder it is for the person to lose weight. There is no clear solution to this problem at the moment. In future, it is hoped that exercise patterns will be discovered enabling people previously unable to slim through exercise to actually lose weight.

Gender differences

Another interesting point about weight loss due to exercise is the difference between men and women. We now know that women are more likely than men to fail in dieting through exercise. Another interesting thing we know from animal experimentation is that more female mice are used for harsh training over several weeks. This is because male mice become unable to eat at some point during training and lose weight, whereas female mice are able to continue eating well and do not lose weight. Women have admirable homeostasis, and one of the reasons why they live longer could be that they have stronger appetites enabling them to eat better. Based on the above, perhaps we have to salute those women who have actually managed to overcome their homeostasis and successfully diet.

Reducing appetite through exercise

Now let's talk a little more about actual life. I wonder if any readers find that they want to eat immediately after doing exercise. The answer is probably no. And there is research that proves this rule of thumb. It is known that immediately after running for 60 minutes, there is reduced appetite and reduced levels of ghrelin, the hormone that stimulates appetite. In my own research, I have shown how appetite falls even after just 30 minutes of jump rope exercise. All this data is biochemical verification of the loss of appetite that everyone feels just after exercising. Furthermore, this reduced appetite continues for about an hour after exercise. So when you feel like having a mid-afternoon snack, why not try doing just a few minutes' exercise instead, such as jumping up and down or climbing up and down the stairs? That's all it takes to lower your appetite, and I expect you will have the added dieting effect of having consumed some energy.

A final word

Controlling bodyweight properly is difficult in this era of abundance when delicious food is so readily available, but it is vital. If you cannot control your weight, you are at risk of metabolic syndrome and lifestyle-related diseases which will prevent you from living a healthy and long life. As I have described here, the impact of exercise on appetite varies from person to person. The first thing is to determine whether you are the type of person who finds it easy or difficult to lose weight through exercise. The only way of knowing this is by practice. Then, by finding a form of exercise tailored to your lifestyle that reduces your appetite, you should be able to control your bodyweight more easily.

Hiroshi Kawano
Assistant Professor, Faculty of Sport Sciences, Waseda University

Born September 5, 1979

March 2008 PhD in Human Sciences from the Graduate School of Human Sciences, Waseda University
April 2008-March 2011 Assistant, Faculty of Sport Sciences, Waseda University
April 2011-present Assistant Professor, Faculty of Sport Sciences, Waseda University

1. Kawano H, Tanaka H, Miyachi M. Resistance training and arterial compliance: keeping the benefits while minimizing the stiffening. Vol.24, pp.1753-1759; 2006.
2. Kawano H, Tanimoto M, Yamamoto K, Sanada K, Gando Y, Tabata I, Higuchi M and Miyachi M. Resistance training in men is associated with increased arterial stiffness and blood pressure but does not adversely affect endothelial function as measured by arterial reactivity to the cold pressor test. Vol.93(2), pp.296-302; 2008.
3. Kawano H, Nakagawa H, Onodera S, Higuchi M, Miyachi M. Attenuated increases in blood pressure by dynamic resistance exercise in middle-aged men. Vol.31(5), pp.1045-1053; 2008.
4. Kawano H, Motegi F, Ando T, Gando Y, Mineta M, Numao S, Miyashita M, Sakamoto S, Higuchi M. Appetite after rope skipping may differ between males and females. Vol.6(2);pp.e121-e127; 2012.