While one person may see great change in their fitness levels and weight as a result of an exercise programme . . . another may see very little difference, despite using the same programme. It's genetics, writes Hélène Hofman
For decades medical professionals have recommended a combination of healthy diet and active lifestyle to lose weight. However, an increasing number of studies show that this may not be the best response for everyone and that how our bodies respond to exercise could be genetic.
"There have always been people who respond well to exercise and others who respond less well," says Dr Donal O'Shea who works with morbidly obese patients at the weight management clinic in St Colmcille's hospital in Loughlinstown, Dublin.
"Some do what they're told and lose weight, others duck and hover. For a long time we thought that was down to psychological issues - maybe that they were finding it hard to stick to their diet - but now it makes perfect sense that there could be something more to it," he says.
According to researchers at the Pennington biomedical research centre in Louisiana, while some people respond well to exercise there is a group of people who will struggle and it will make little or no difference to their weight or levels of fitness when they increase their levels of activity.
The scientists put 742 completely sedentary people through a 20-week training programme that increased in intensity over the duration of the experiment. When they measured the fitness of participants at the end, they found that while some participants had improved by 40 per cent, in some there had been no change at all.
Speaking to the Guardian newspaper earlier this month, Dr Claude Bouchard, the study leader, said: "The discrepancies in the individual response to exercise are remarkable, even when the training people undergo is identical . . . For any given indicator of fitness, there appear to be people who have a quick and large response (high-responders), people who have a slighter response (low-responders) and some who see no change at all (non-responders)."
However, Dr Bouchard said that although some participants had not improved across all the markers of fitness, which included cardiac output, insulin resistance, blood pressure during exercise and pulse rate - all of them had benefited in at least one category.
Dr O'Shea agrees that people react to exercise differently, and from a weight loss point of view he has identified what appear to be 'low responders'.
"People are designed to expend energy in different ways. What's right in general and for the population at large may not be right for everyone," he explains. "When you're losing weight you're trying to cod your body. The body does not like to lose weight. When we do surgery someone who is 35 stone may come down to 26 stone but they won't come down to 12 stone. The body is good at protecting its body weight," he says.
According to Dr O'Shea, 60 per cent of people who embark on a weight-loss plan will lose about 5 per cent of their body weight. However, he also says that although exercise may have minimal benefits from a weight-loss point of view for some people it may have other advantages.
"Exercise has two roles. One is getting people cardiovascularly fit and then there is this role of weight loss. I have seen people respond very slowly but I have never seen anyone that didn't respond at all," he says. "We may have been looking at genes for the wrong reasons up until now and hoping they might provide a single answer. There are hundreds of genes clearly linked to causing obesity. What they may be used for in future is predicting the right kind of treatment and identifying the people who may become obese".
Although there has been little research into this area in Ireland, James Dwyer, a researcher in the physiotherapy department of Trinity College Dublin and physiotherapist at St Columcille's weight management clinic, says it is evident that some people react better to exercise than others.
"Any evidence at the moment is anecdotal but we have patients who come in and say that no matter how much they exercise it doesn't make a difference. Then you look at their neighbour who says that as soon as they picked up their activity levels it made a difference," he says. "But it's difficult to measure what exactly made the difference. People react to exercise in different ways. If you were to stand beside your twin on a treadmill and both run at three miles an hour you would expect to burn the same calories. But one twin may have a cold and that would affect their metabolic rate, or their ability to get oxygen to the muscles or they may simply have a different walk.
"Similarly age can play a part, if you stand next to someone 20 or 30 years older than you you would react differently to the exercise," he says.
He also explains that men and women react differently to exercise. A study conducted by Joseph E Donnelly, director of the Center for Physical Activity and Weight Management at Kansas University found that men burned calories faster than women.
"He found that women come off a treadmill after 50 minutes and men after 30 minutes having burned a similar number of calories.
"Testosterone builds muscles and in most cases men have a greater muscle mass and a bigger engine burns more calories. Men get off the treadmill quicker, they burn the calories faster," he says.
However, Dwyer points out that regardless of how many calories are burned or whether it results in weight loss or not, exercise will always be beneficial.
"Just because somebody is getting less weight loss from exercise that is only one component. Exercise makes you less likely to suffer from coronary problems, respiratory problems, type two diabetes, depression and other diseases.
"It doesn't matter how much or how litte calories are burned they will always benefit you in some way and it is useful whether you're trying to lose weight or not," he says.
There are people who will struggle with exercise and it will make little or no difference to their weight or fitness