Weight loss: Can exercising help to keep the weight off?

People who try to lose weight by dieting and doing exercise could lose about 20 percent more weight than people who only diet. One year after losing weight the people had gained about half of the weight they had lost. But those who did exercise weighed less than those who were physically inactive.

A lot of people are unhappy with their weight and would like to lose weight and keep it off. Many diets and other strategies are claimed to help people lose weight, but such claims are often based on short-term success stories or the experiences of people who were particularly enthusiastic about a certain method. This means that we do not know how common it is for people to put on weight again once they stop following their weight-loss programme. It is often difficult to keep weight off in the long term.

Combining a diet and exercise is the most commonly recommended way to lose weight. A lot of different factors can influence whether people lose or gain weight, so it is difficult to say which weight-loss strategy is most suitable. The best way to find out for sure whether a certain approach works or not is with randomised controlled trials.

When researchers carry out a trial like this on weight loss, they look for people who would like to lose weight and who volunteer to follow a programme or approach which is chosen for them, rather than choosing a weight-loss strategy themselves. The participants are then divided into groups. For example, one group may try to lose weight by doing exercise and dieting, and another group is the comparison or control group. The people in this group could be asked, for example, to only go on a diet, or not to change their lifestyles at all.

This means that the only difference between the people who do exercise as well as going on a diet and the other participants is that they are following their special programme. So, for example, they are not any more motivated than others to do exercise. If they lose more weight than other participants, it is likely that this approach would also work for other people.

Researchers at the University of Rio de Janeiro wanted to find out if there is a reliably proven difference between only dieting and both dieting and doing exercise in long-term weight loss. The researchers looked for relevant trials in which the participants were followed up one year after the actual study had finished. The participants had to be over 18 years old and overweight. In other words, they had to have a body mass index (BMI) above 25.

The BMI is a measure which describes the relationship between body weight and height. A BMI above 25 indicates that the person is overweight, and a BMI over 30 is considered to be obese.

The researchers found 33 trials in total, but only six of these compared dieting alone with dieting and exercise. Still, this was enough to help answer the question of whether exercise makes a difference. The trials were carried out in Finland and the USA. Only slightly more than 400 people took part in the trials altogether. This means that better and larger trials are needed to be able to say what kind of weight-loss programme is most likely to lead to long-term weight loss.

Another problem with these trials was that they reported how much weight the participants had lost, but did not report how many of the participants had lost weight. This means that the researchers were not able to say how likely it is that people will lose weight if they only go on a diet or also do exercise. However, they were still able to draw some clear conclusions. The participants who both dieted and did exercise lost more weight: They lost 13 kg (29 pounds) on average, compared to 10 kg (22 pounds) in the group that only dieted. In other words, people lost about 20% more weight if they did exercise too.

This group of participants lost 3 kg (7 pounds) more on average. The amount of weight that each person lost varied greatly, which depended on factors like how much they had weighed to start off with. The people who followed weight-loss programmes involving both a diet and exercise weighed between 80 and 113 kg (between 176 and 249 pounds) at the beginning of the trial. Although they lost 13 kg (29 pounds) on average, some of the participants only lost 3 kg (7 pounds), whereas others lost 23 kg (51 pounds).

After one year the participants had gained half of the weight they had lost, regardless of whether they had also done exercise or only dieted. But because those who had also done exercise had lost more weight on average, they still weighed less one year after the weight-loss programme had finished: about 7 kg (15 pounds) less on average. The most weight that had been kept off was 15 kg (33 pounds), but some people even weighed more than they had to start off with. According to the researchers, the trials show that the people who lost the most weight were also more likely to put on weight again. It appears to be easier to keep off weight in the long term if you lose less weight.

So what can we conclude? People lose more weight if they do exercise in addition to dieting, but are not more likely to keep the weight off than people who only diet. Still, the weight loss is greater overall because they lost more weight to start off with.



Author: German Institute for Quality and Efficiency in Health Care (IQWiG)

© IQWiG (Institute for Quality and Efficiency in Health Care)