If you're slim, don't think you can get away with not exercising - you still risk heart problems if you don't hit the gym, a study suggests.
Research suggests thin people need to spend time on the treadmill
The London-based team measured the levels of heart-clogging cholesterol (LDL) in 37 lean exercisers, 46 lean and 28 obese non-exercisers.
They found lean exercisers had good LDL levels, but those in lean and obese non-exercisers were higher and similar.
The study is published in the International Journal of Obesity.
It concluded that exercisers were fitter and leaner than those who were sedentary, and had a better chance of not developing cardiovascular disease.
Dr Gary O'Donovan, exercise physiologist at Brunel University, said: "Many people, especially slim people believe that they only benefit that can be achieved from exercising is weight-loss.
"This is not the case. Our study suggests that slim people need to exercise as much as others in order to stay healthy and keep LDL cholesterol in check."
Dr O'Donovan said he devised the study to look at how exercise affected a person's health profile.
It was already known that aerobic fitness was amongst the most reliable measure of health now and in the future and that those who did well in fitness tests were likely to live around five years longer, he added.
For the study he divided his 113 non-smoking men aged 30 to 45, with similar socio-economic profiles, into three groups - lean exercisers, lean non-exercisers and obese exercisers.
Obesity was classed as a person with a waist of more than 100cms, measured at the narrowest point.
An exerciser was someone who took regular cardiovascular exercise, such as running or cycling, three times a week or more.
Dr O'Donovan suggested that, because the profiles of the men were the same, it was a reasonable assumption that the differences in cholesterol results were linked to whether the person exercised or not.
He added: "The benefits of exercise are not just about maintaining a normal weight.
"There's some quite convincing research that shows that habitual exercisers live a little longer."
Dr Charmaine Griffiths, spokesperson for the British Heart Foundation (BHF) said exercise was essential in maintaining a healthy heart - no matter what your body shape.
"We know that for some people a low fat diet can help keep their cholesterol level low, whilst for some their blood cholesterol stays high no matter how thin they are.
"We can all take steps towards a healthier heart by eating a balanced diet and taking at least 30 minutes of moderate physical activity five times a week."
Dr O'Donovan now wants to look at the bad cholesterol levels of obese exercisers - the so-called "fat fit".
If such a study found that LDL-cholesterol was similar in obese exercisers and lean exercisers, it would suggest that habitual exercise lowers heart disease risk independent of body fat.
Dr O'Donovan says: "We have started looking for volunteers to take part in the next phase of the study.
"Basically, we're looking for the Jason Leonard's of the world - men who regularly exercise but have a large frame!"
Those interested in volunteering for the next phase of the study should call Dr Gary O'Donovan on 01895 266 481 or email firstname.lastname@example.org.