Obesity gene disrupts appetite signals

Children with two copies of the higher-risk gene, known as FTO, tend to find it difficult to recognize when they are full-up, according to researchers at UCL (University College London) and the Institute of Psychiatry, King’s College London, who are trying to unravel how the gene works.

Previous studies have demonstrated that FTO is strongly associated with obesity but it was not known whether it affects weight by influencing the amount of food eaten or the amount of calories burnt off.

The study of more than 3,000 children, published in the Journal of Clinical Endocrinology & Metabolism, indicates that the gene modifies appetite so that children with two copies of the ‘risky’ genes are less likely to have their appetite switched off by eating.

Lead author, Professor Jane Wardle, UCL Epidemiology & Public Health, said: “While recent research has shown that the FTO gene is strongly linked with children’s body weight and food intake, this study tells us more about how the gene could be exerting its effect.​

“What we have shown is that children with the ’risky’ variants of the gene have weaker satiety responses – meaning they don’t just overeat, but they struggle to recognize when they are full. Importantly, the effect of FTO on appetite is the same regardless of the age, sex, socioeconomic background or body mass index of the children. ​

“It is not simply the case that people who carry the risky variant of this gene automatically become overweight – but they are more susceptible to overeating. ​

“This makes them significantly more vulnerable to the modern environment which confronts all of us with large portion sizes and limitless opportunities to eat.“​

Prof Wardle added: “All of us in the health area who are concerned about growing body weights in children and adults would welcome anything that the food industry could do to help people make better eating decisions – to nudge them towards better consumption and nudge them away from over consumption.” ​

FTO is the first common obesity gene to be identified in Caucasian populations. Previous studies have shown that adults with two copies of the FTO gene are on average 3kg heavier, and individuals with a single copy are on average 1.5kg heavier, than those without the gene.

The researchers tested whether children carrying the higher risk gene had altered appetite in a sample of 3337 unrelated children aged 8-11 years old, in the UK.

This included parental reports of the children’s height, weight and waist circumference and asking parents to complete a specially-designed questionnaire about their children’s eating habits, to assess aspects such as their child’s enjoyment of food and how easily they became full.

The obesity debate​

Last year Dr Siân Astley from European Nutrigenomics Organisation (NuGO) said there are more than 600 genes currently associated with obesity.

These genes interact with one another and with our environment, including diet and lifestyle, to impact an individual's risk of becoming obese. But, she added that obesity is a highly complex disease and includes not only biochemical but also physiological and social issues.

The new study highlights the complexity of the obesity issue and adds to a wealth of research, including a recent study, also by UCL researchers, which suggested that genetics and heritability may account for 77 per cent of obesity, while environmental factors make up less that 25 per cent.

Meanwhile a lot of focus has been placed on the food industry to reformulate their products, provide clear labelling and reduce advertising to children.

Portion control ​

An estimated 25.6 percent of US adults reported being obese in 2007, compared to 23.9 percent in 2005 which is an increase of 1.7 percent, according to a study published in Morbidity and Mortality Weekly Report this month.

Experts say that efforts need to be made to reduce these figure and this provides opportunities for food and beverage manufacturers to position consumer products that address the obesity phenomenon.

One trend is for portion control, which is quite big in the US, according to Leatherhead.

An example of this is Mars Snackfood US which announced earlier this year that its Dove chocolate tablet bar collection would feature three individually wrapped pieces in a re-closeable pack "addressing consumers' desire for portion control, portability, share-ability and freshness".

A Datamonitor study earlier this year called "Obesity, Dieting, Exercise and the Future of Food and Drink - Understanding consumer attitudes and behaviors" said that despite active attempts to eat healthily, obesity prevails because of lifestyle changes and food choices.

The analyst drew up recommendations for the industry, among them that companies need to find means to work with their existing portfolio by using portion control and labeling to help consumers make healthy choices.

Source: Journal of Clinical Endocrinology & Metabolism​

Published online ahead of print, doi:10.1210/jc.2008-0472

“Obesity-associated genetic variation in FTO is associated with diminished satiety"​

Authors: Jane Wardle, Susan Carnell, Claire M. A. Haworth, I. Sadaf Farooqi, Stephen O'Rahilly, and Robert Plomin