If you're fat and fit, you're likely to live a lot longer than if you're thin and unfit. While this isn't the perception of the general public, it's one of a whole raft of discoveries that sport and exercise scientists have made in their exploration of the obesity epidemic.

Most people think sport and exercise scientists exist to make people better at competitive sport. They visualise them trying to get an Olympic gold medallist another gold medal. But in reality many sports scientists are as likely as you or I to ever be in the same room as a sports star. Instead, they have opted to do research or front-line work (or both) in an attempt to make the rest of us more fit and healthy.

With the World Health Organisation predicting that there will be 2.3 billion overweight adults in the world by 2015 and more than 700 million of them will be obese, obesity is clearly an area in desperate need of addressing. For many sport and exercise scientists, it is an area too good to miss if they are to bring about real change.

"There is definitely an opportunity to make a difference," says Gordon McGregor, clinical exercise physiologist at University Hospital, Coventry.

He provides the example of his discovery that regardless of body weight or body fat, people who are fitter survive longer.

"A lot of the research into obesity points to it being a key factor in increasing mortality. In fact, when you break this research down, it isn't robust. What is robust is the evidence that points to lack of fitness causing people to die younger or suffer with high cholesterol, diabetes or a number of other things. There are other studies that have been done in the States that back this up."

McGregor and his colleagues also found that society's obsession with weight loss is actually detrimental. "Constant weight cycles are bad for you and dieting doesn't tend to work. The focus should be on improving fitness. It may be that as a result, you lose weight anyway, but the health benefit comes from the fact that you're fitter."

The real crux of his work is that, like other sport scientists, McGregor is able to promote his findings to a wide range of professionals who are then able to incorporate it into their work with obese people.

Besides carrying out research, McGregor also has a day-to-day clinical role with people in cardiac rehab, many of whom are obese. This work, he says, is equally rewarding. "I get people coming to see me, many of whom have never contemplated putting on a pair of running shoes. But even after just six weeks, they come to me and say how life-changing it has been. As they get fitter, they get renewed enthusiasm about other things in life."

McGregor predicts an increase in the number of sport and exercise scientists employed by the NHS to work in the field of obesity in the coming years. "At the moment, only about 30 NHS trusts employ them to do this kind of work. But as the NHS gets more switched on to what this profession is all about and as they become more focused on obesity, they will undoubtedly take on more people," he says.

Those who join the NHS, he says, will need to be able to create a rapport with unhealthy patients. "Even if you're the greatest exercise scientist in the world, if you can't relate to these people, you won't get anywhere. This area of work is as much about human behaviour as science."

Dr John Buckley, the senior lecturer in exercise physiology and cardiovascular health at University of Chester, agrees. "The problem is that you get a lot of people coming into sport and exercise science because they are into sport and exercise themselves. Therefore there's a good chance they may not naturally understand why someone hasn't opted for sport in their lives. But only 20 to 30 per cent of the population do like sport and exercise. It's critical to understand the other 70 to 80 per cent of the population if you're going to succeed in this field," he explains.

Armed with empathy, your next step will be to do a degree in sport and exercise science. Buckley advises choosing a degree which incorporates counselling and exercise instruction.

"Many degrees are now offering these vocational areas, but not all. Have a look at the curriculum and double check," suggests Buckley, who is the exercise science practice adviser for BASES (the British Association of Sport and Exercise Sciences).

He adds that you should be prepared to go on to study postgraduate qualifications, particularly if you envisage a research-based career. "The undergraduate degree only lasts three years and doesn't explore issues like the heart and cardiovascular disease in enough detail for someone wanting to specialise in obesity. I'm not talking about a PhD necessarily, but a Masters degree, which would be 12 months full-time."

Besides the NHS, there are other employers of sport and exercise scientists focusing on obesity, he says. "There's a growing market in private leisure facilities, as well as public leisure facilities, for instance."

Anna Doolan, project manager at Bromley Mytime Leisure Trust, explains that they provide all the leisure centres and facilities such as golf courses and swimming pools – as well as places such as soft play areas and after-school clubs for children – across the borough. Among the programmes that she, as a sport and exercise scientist specialising in obesity, is involved in is MEND (Mind Exercise Nutrition and Do-It), a family centred, multidisciplinary approach to prevention and treatment of obesity in children.

The eight-week programme combines education sessions and exercise that is either pool or land based. "The two together are the best way to overcome obesity," Doolan explains. "There are many other projects I'm involved in around childhood obesity too. The Government has set high targets to tackle the issue and while we are making a huge amount of difference at the top end – the people who are most obese – the next stage is to catch them before they get to that stage."

Even four years ago, people were reluctant to put money into this area, she says. "But not now. There's a huge amount of partnership working to tackle the epidemic. I think we'll see a lot more jobs for sport and exercise scientists."

Not everyone opts for clinical practice. Dr Jason Gill, an exercise scientist at the Institute of Biomedical and Life Sciences at the University of Glasgow, focuses entirely on research around obesity and related issues.

"What I'm interested in at the moment is how physical activity can help control energy balance," he says. "Obviously, if you exercise and burn more calories you're increasing energy expenditure that should make you lose weight. But there is a feedback loop to energy, so actually if you exercise you might get hungrier and eat more. So if you run five miles and burn 500 calories, you might not be 500 calories in deficit because you eat more food. So we're working out the net effect of this."

Studies like this can help fight obesity, he says, because we need to understand more about the causes of weight gain before we know what to do about it. "It's not as straightforward as, 'You're overweight, you need to burn more calories' because if you burn more calories, you may eat more calories."

With growing awareness about the link between obesity and conditions like diabetes, people like Gill are also studying this area.

Researching such areas of sport and exercise science is no mean feat, says Gill.

"It's very hard work. But you get to find answers to things that nobody else knows the answers to. That's a huge buzz. Then you get to share that information for the greater good."

'I don't just promote sport but also things such as walking to school'

Gareth Stratton's key role is to find ways and means to promote physical activity among children.

"I'm not just talking about sport, but also things such as walking to school and doing chores round the house," says the professor of paediatric exercise science at Liverpool John Moores University.

In one study, he's measuring whether seemingly small changes made to a child's life can make a difference to their health outcomes. "I use detailed technology which ranges from a simple pedometer to a GPS system. We also measure things like their heart rate."

Another project he's running with other partners involved 160 children being divided into four groups. One group was introduced to high intensity structured exercise; another to skilled exercise involving different shaped balls and other equipment; another to lifestyle based missions; and another to health information, but no treatment. "It was a very complex research design, with lots of measurement, and we'll have the data analysed in three months' time. Once it's published, it will be taken up by organisations such as the obesity task force in Liverpool."

One of his study findings was recently published in the British Medical Journal. "We were interested in whether adolescents playing with the Nintendo Wii expanded more energy than sedentary computer games. We measured the energy they expended when playing games on the computer like tennis and boxing. We found they did use more energy, although not compared to the real thing. The idea was to get rid of the blame culture of computer games when it comes to the obesity epidemic."

There are plenty of other examples of how exercise and sport scientists can help fight obesity in children, he says.

"We did one project across 21 schools in Liverpool where we split the playground into three very attractive zones – a red zone for high activity; a blue zone for more individual activities; and a yellow zone for chilling out. We demonstrated that children's activity was higher, even a year after the zones were introduced."

Grey anatomy: Exercise for older people

There aren't many health clubs where the average age is 65. But the health and fitness facility which John Buckley is involved in, has a programme aimed exclusively at older people.

The senior lecturer in exercise physiology and cardiovascular health at the University of Chester explains: "A lot of the environments which we create for people to participate in exercise turn older people off. There is a psychological barrier, which isn't surprising when you look at the programmes they offer and the way they market them. In most cases, the marketing exercise is about telling people they can look different and they get enticed into physical exercise simply because they want to look like their favourite movie star or footballer – even though this is a false dream."

He adds: "Another reason that older people often aren't catered for is because it requires appropriately trained staff. There are greater risks of strokes, heart problems and falls."

Sport and exercise scientists have the opportunity change this. "It's about asking questions like, how do older people perceive these exercise settings? How do they relate it to themselves?"

The next step is putting it into practice. "We have trained staff and have created a user-friendly environment. As we become an ageing population, the industry will have to change and people like us can help them work out how to do it best."