Unable to resist the urge to eat
When blood glucose levels fall, the brain starts to crave high calorie foods, particularly in those who are already overweight, research suggests.
The craving comes from an area of the brain involved in regulating emotion and impulses, and the ability to resist the desire to eat is lost.
In the study, the researchers manipulated blood sugar levels of obese and non-obese volunteers using intravenous infusions.
Changes in blood sugar levels were monitored while the participants were shown pictures of high calorie foods such as burgers, chips, chocolate and ice cream, low calorie foods such as broccoli, fruit, salads and bean sprouts, and items that were not food.
As this was happening, the scientists scanned changes in their brains using functional magnetic resonance imaging (fMRI).
When glucose levels fell, two 'reward' areas of the brain - the insula and striatum - were activated, inducing a desire to eat.
But, another area of the brain - the prefrontal cortex - which usually prevents impulsive behaviour, appeared to lose the ability to inhibit the urgent 'eat' signals being generated in the striatum.
Researchers said the weakened response was particularly striking in the obese volunteers when they were shown pictures of high calorie foods.
Dr Kathleen Page of Yale University, who co-led the study, said:
"Our results suggest that obese individuals may have a limited ability to inhibit the impulsive drive to eat, especially when glucose levels drop below normal."
Researchers suggested that maintaining stable glucose levels by eating healthy foods such as complex carbohydrates and fruit and vegetables may help people maintain a healthy weight.
The study is published in the Journal of Clinical Investigation.
