Klaas Westerterp Klaas Westerterp Sacha Ruland

Overweight? Exercise is not the answer

In Body
Written by  Annelotte Huiskes Wednesday, 11 September 2013 07:30
Valedictory lecture by Klaas Westerterp

Trying to drop a few kilos by heading to the gym or going for a jog twice a week? Forget it. You won’t lose weight from exercising – but you will from eating less. “The problem is overeating to begin with. Once you’re overweight already, the problem is usually irreversible.” This is what Klaas Westerterp, professor of Human Energetics, will have to say in his valedictory lecture ‘Energiebalans in beweging’ on 12 September.

“Strenuous workouts now and then have little to no effect on your energy balance”, Westerterp explains. “People who exercise more use more energy, but that often means they also eat more. In one of the clearest studies we’ve done in this area, we spent a year training participants to run a half marathon. Their energy expenditure increased by 25%, which is quite a lot and not something you see often, especially not over a longer period. The participants were selected for the fact that they were inactive; they weren’t athletes but office workers, for example. We also had them keep a record of what they ate. Two things emerged from that study. Their energy expenditure increased enormously, so much so that had they continued to eat what they normally ate, they would have lost 15 kilos. But their weight remained the same. From what they reported themselves their food intake didn’t change. In other words, they didn’t think they were eating more, but they were. The whole problem is that people don’t know what they eat – or they don’t want to know.”

The key, according to Westerterp, is the energy balance: the relationship between energy expenditure and energy intake. As a biology undergraduate in Groningen he studied the energy expenditure of starlings, and during his PhD he worked with rats, studying energy expenditure in the case of malnutrition. On his arrival in Maastricht in 1982, Westerterp introduced a new method for measuring energy expenditure in humans. “In Scotland I’d studied swallows to see how they use energy to fly. I learned a technique there that allows you to accurately measure energy expenditure using labelled water. In Maastricht, we applied this technique in people for the first time. But it’s an expensive method, and you also want to be able to say something about the activity from minute to minute. So we developed a device here, the accelerometer, that you carry with you which measures precisely when you’re active. I’ve had one on me for five years myself."

Losing weight

In his roughly 30 years in Maastricht, Westerterp has also done a great deal of research on the effects of dieting on the energy balance. Here, too, he sees the same result: exercise does not lead to additional loss of body weight. “In one study participants were put on an energy-restricted diet for some weeks and lost a lot of weight, say a kilo a week. But at the same time they exercised less, because they were getting less food and so less energy. But if you put people on the same energy-restricted diet and an exercise programme, they lose the same amount of weight. This is because they do their one hour a day of supervised exercise, but all the time they aren’t being monitored they exercise less to compensate for that extra exercise. If you exercise a lot and don’t eat, you end up with a negative energy balance and you feel weak, so this compensation is a very normal physical reaction in the case of a negative energy balance. Let me be clear: exercise is of course very healthy, provided you don’t push your body too hard – but it won’t make you lose weight.”


Ideally, our energy intake is equal to our energy expenditure. Unfortunately, more and more people today have a positive energy balance: more energy goes in than is actually used, leading to overweight. So do we exercise less these days? “So far there are no indications that we spend less energy on activity than we used to. We have data here, including from research using labelled water, that we can compare over a 25-year period. The results show that the energy humans expend during physical activity is the same as an animal of approximately our size living in the wild. So it’s not the case that we’ve started exercising less, as is often thought now that we live in a high-tech world and spend a lot of time behind our computer screens.”

Diet advice

The growing problem of obesity, in Westerterp’s view, is not because we have started exercising less but because we simply eat too much. Just eat less, is his advice – but then, that’s exactly the thing that seems to be so hard. “What you should be doing is preventing the development of overweight, because whether we’re talking one, five or a hundred kilos, it’s unlikely you’ll be able to get rid of it. In general, overweight is irreversible. So the best thing is not to put the weight on in the first place. Maintaining your weight is perhaps also a better goal than losing it, because studies show that long-term diets usually have no effect. Be aware of what you’re eating; people often just don’t realise how easy it is to eat too much. A big problem nowadays is soft drink. Get rid of soft drinks and you’ll go a long way, because the amount of energy you get from them in addition to your normal food intake is enormous. But then you come up against the food industry and it becomes politically sensitive. The advice to exercise more is less touchy, but it doesn’t help, unlike a small difference in energy intake per day, which has a major long-term effect on energy balance. It may not be an easy message to sell, but it is one that’s based on scientific research.”

Klaas Westerterp will deliver his valedictory lecture ‘Energy balance in motion’ on Thursday 12 September at 16.00 in the Aula, Miderbroedersberg 4–6, Maastricht.

Rate this item
(9 votes)
Read 39242 times
You are here: Home Research Body Overweight? Exercise is not the answer

Maastricht University Webmagazine

Marketing & Communications
Postbus 616, 6200 MD Maastricht
Minderbroedersberg 4-6, 6211 KL  Maastricht
Tel: +31 43 388 5222
This email address is being protected from spambots. You need JavaScript enabled to view it.

Download UM Magazine

Read a digital version of Maastricht University magazine,
or download the PDF.
UM Webmagazine June 2017

Connect with us