Fat children are more vulnerable to food advertising than their healthy weight counterparts.
Research by scientists at the University of Missouri-Kansas City and the University of Kansas Medical Centre found that obese children have much less self-control than healthy weight children.
By assessing 20 children - 10 obese and 10 healthy - the scientists were able to look at the differences in brain activity when presented with images of food logos.
Researcher Amanda Bruce said: "We were interested in how brain responses to food logos would differ between obese and healthy weight children."
Obesity can increase the risk of a number of diseases, including cancer and heart disease. NHS figures show that 30.3 per cent of children aged between two and 15 are now either overweight or obese.
They show that 16 per cent of children are classified as obese - having a body mass index of 30 or above.
People become obese by eating too much and exercising too little, but it can also be caused by genetic conditions.
In the UK, the food and drink industry has been asked to play a greater part in supporting people in making healthier lifestyle choices through the Responsibility Deal, including calorie labelling on menus.
However, food advertising in the US is thought to be a contributing factor to childhood obesity rates tripling over the last 30 years. Research shows that 98 per cent of food products advertised to children across the pond are high in fat, sugar or salt.
As a result of the growing problem of childhood obesity in the US, Michelle Obama launched the Lets Move! campaign in 2009 to encourage children to exercise and eat healthier food.
In the study, the children were showed 60 food logos and 60 non-food logos. Their MRI scans showed which sections of the brain reacted to the logos.
Obese children had a greater reaction in the reward regions of the brain compared with the healthy weight children, who showed greater activity in the regions associated with self-control
Bruce said: "This study provides preliminary evidence that obese children may be more vulnerable to the effects of food advertising.
"One of the keys to improving health-related decision-making may be found in the ability to improve self-control."