The sweet science: Our uncontrollable cravings for treats are triggered by falls in blood sugar
You might have thought resisting that piece of chocolate cake or extra biscuit was simply a matter of exerting a little will power. But for some of us it’s much more difficult than that – because of the way our brains are wired.
Scientists have found that a key part of the brain which stops the body from acting on impulse
– and gorging
– does not function as well in those who are overweight or obese.
A study by scientists from Yale University has shown that falling glucose
levels lead to a loss of self-control in the brain which subsequently lead to parts of the brain craving high-calorie food such as cakes, biscuits or crisps.
In obese people the effect may be even more pronounced, so they are driven to eat by the slightest drop in glucose.
Glucose is normally obtained from carbohydrate
foods, which can come in healthy and less healthy forms.
Scientists believe the phenomenon occurs because of the brain's huge demand for glucose, which it needs as energy fuel.
'Good' carbs include fresh fruit and vegetables, brown rice and pasta, nuts, wholemeal bread, and beans.
Among the 'bad' varieties are white bread, white sugar, biscuits, cakes, crisps and other packet snacks, carbonated
soft drinks, ice cream and corn syrup used in processed foods.
Ensuring adequate brain glucose levels - in a healthy way - might make it easier to stay slim, the research suggests.
“The key seems to be eating healthy foods that maintain glucose levels. The brain needs its food,” said Professor Rajita Sinha, from Yale University in the U.S., who led the study.
The research is reported today in the Journal of Clinical Investigation. Prof Sinha's team manipulated blood sugar levels in a group of volunteers with intravenous injections of glucose.
At the same time, participants underwent functional magnetic resonance imaging (fMRI) scans of their brains while being shown pictures of high-calorie and low-calorie food, and non-edible
The scans showed that when glucose levels fell, two 'reward' regions of the brain that make certain activities pleasurable induce a desire to eat.
But the most pronounced reaction was seen in the prefrontal cortex
, the 'sensible' part of the brain that prevents people acting on impulse.
When glucose levels lowered, the prefrontal cortex lost its ability to reign back the urgent 'eat' signals.