Some people may have a higher risk of obesity because they are genetically predisposed to overeat or lead a sedentary lifestyle, a leading Cancer Research UK scientist will told conference delegates last week.
Speaking at the charity's second Senior Researchers' Meeting in Harrogate, Yorkshire, Professor Jane Wardle will say certain differences in genetic make-up are likely to influence an individual's attitude to food and physical activity.
The differences could explain why some people find it much harder than others to turn food down when they are not hungry or motivate themselves to exercise.
Obesity is linked to post-menopausal breast cancer and cancers of the womb, gall-bladder and kidney. There is also some evidence that it raises the risk of prostate cancer and cancers of the colon, rectum and pancreas.
Prof Wardle believes understanding the underlying factors behind obesity can help prevent the condition and, in turn, help prevent cancer.
Her team at the Cancer Research UK Health Behaviour Unit are looking into the reasons why children of obese parents have a substantially higher risk of obesity than children of lean parents.
They have compared food and activity preferences in over 400 twin children of overweight parents and normal weight parents. They found that children with overweight parents had a higher preference for fatty-foods and sedentary activities, a lower liking of vegetables and were more likely to overeat.
The team are now looking to distinguish whether these preferences have a genetic basis or are due to environmental factors that are shared within the family.
In the new study they are looking at the same group of children but this time they are comparing the food and activity preferences of twins that are identical with those that are non-identical.
Twins share the same environment so scientists can filter out any environmental influences on a trait and focus on genetic factors.
Identical twins are from the same egg and have 100 per cent of their genes in common while non-identical twins come from two separate eggs and, like any sibling, share on average 50 per cent of the same genes.
So, if a trait is genetically influenced then identical twins will be more similar for that trait than non-identical twins. If, on the other hand, a trait is heavily influenced by shared environmental factors identical and non-identical twins should be equally affected.
The preliminary results of Prof Wardle's study show that identical twins are more alike in their food and activity preferences than non-identical twins – suggesting that there is a genetic basis to these traits.
Prof Wardle says: "Our early results show that genes play an important role in determining people's food and activity preferences. These genetic differences may explain why some people find it harder to stay a healthy weight and avoid obesity.
"It also helps explain why children of obese parents have a substantially higher risk of obesity in adulthood than children of normal weight parents.
"In the future we should be able to find genetic markers that predict obesity risk more precisely. This would help identify those who need more help in controlling their weight," she adds.
Prof Wardle believes that genes linked to food and activity preferences are only likely to cause small changes in behaviour. For example people who have a genetic predisposition to overeat may only eat slightly more than necessary rather than binge eat.
She says: "It's important to note that these genetic differences are only likely to cause subtle changes in behaviour. For example someone with an inherited tendency to overeat may take just one extra biscuit from the packet than someone with more control.
"However, over a number of years, these 'extras' would lead to an accumulation of body fat."
Dr Lesley Walker, Director of Cancer Information at Cancer Research UK, says: "Professor Wardle's work suggests that some people may be particularly prone to unhealthy lifestyles that could lead to obesity and possibly cancer.
"We need to find new approaches to identify those who are more susceptible to obesity and work out ways to change behaviours that may be more ingrained."