Why some are prone to obesity

Some women can manufacture fat more easily

Scientists may have found a reason why some women have a tendency to put on weight very easily.

They have found that obese women convert excess dietary carbohydrate to fat faster than lean women.

This process is known technically as de novo lipogenesis.

It may be the case that under certain dietary circumstances some of us are more efficient at storing excess dietary carbohydrate as fat than others

Dr Regina McDevitt

Researchers from the Scottish Agricultural College in Ayr and the Medical Research Council in Cambridge tested the response of lean and obese women to two types of diet.

The first was rich in carbohydrates, but designed to provide just enough energy to meet each woman's daily requirements.

The second was loaded with excess carbohydrates, and designed to provide 50% more energy than the women actually needed.

When the volunteers were fed on the energy-balanced diet, the rate of de novo lipogenesis among the obese women was nearly twice that among the lean women.

High rate

Women who had a high rate of de novo lipogenesis in response to the energy-balanced diet also had a high rate when given the energy-loaded diet.

The researchers say their results suggests that some individuals may have an intrinsically higher, perhaps genetic, potential for de novo lipogenesis.

Lead researcher Dr Regina McDevitt told BBC News Online: "Our data do not suggest that if an individual ate a "healthy" diet to an appropriate energy level that they would go on to develop obesity.

"However, it may be the case that under certain dietary circumstances some of us are more efficient at storing excess dietary carbohydrate as fat than others.

"This would obviously have been an important survival tool in evolutionary terms when food availability was not always predictable, but in the modern Western world, where there is an excess of nutrients and energy, it has become a redundant survival tool."

Small effect

Professor Ian MacDonald, an expert in obesity from the University of Nottingham, said the effect that the researchers had discovered was small, and the study was based on a small sample number (13 women).

However, he said: "The observation that the obese did have an increased ability to make fat from carbohydrate when being fed to energy balance is interesting, because it suggests that if they do overeat slightly, they might find it easier to synthesise fat from any excess carbohydrate.

"It could be genetic, or due to habitual diet and lifestyle."

The research is published in the American Journal of Clinical Nutrition.