Have you ever wondered why you seem to crave junk food and other fattening foods when you're hungry? A new study published in the Journal of Clinical Investigation
shows that the brain makes food look more enticing when you're hungry
--especially if they've got loads of calories and thus a lot of glucose.
The researchers from the Yale University and the University of Southern California examined 14 people
from three weight groups (healthy, normal, and obese), all of which had eaten two hours before to make sure they were neither hungry nor full. They regulated the participants' glucose levels
intravenously through a device and interpreted the results via a functional MRI scanner. While hooked to the device, they showed the participants pictures of high-calorie and low-calorie foods as well as non-food.
The results showed that when glucose levels were normal, the participants' prefrontal cortex
was more active. This part of the brain governs over logic and reasoning, which means the participants' food cravings were kept in check.
As the glucose levels dropped, though, the hypothalamus, thalamus and nucleus accumbens became more active. These control the body's reward system
and trigger a survival response as the need to refuel the body becomes more and more urgent. One of the brain's surefire ways of urging you to eat is by making food look delicious
, and the higher the amount of glucose
in them, the more attractive they start looking to you.
After the body gets the calories it needs and your glucose levels are up, the prefrontal cortex kicks in again, and food returns to looking normal. However, the researchers found that this doesn't seem to happen for obese people. Instead, the food continues to look attractive to them, thus fueling their desire to eat.
"We don't know why, and we don't know if it's reversible, but these results imply that there may be a biological difference that when people become obese, their motivation for eating when they see an ad or picture may not be under the same control systems as those of lean people," says Robert Sherwin
, lead author of the study and professor of medicine at Yale.
How do you control your cravings, then? Don't let yourself get to the point where you're starving. The hungrier you get, the more likely it is for you to consume more high-calorie foods. If you eat on time and have the proper amount of food, you'll be more likely to control your body's reward system.
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(Photo by ebruli via Flickr Creative Commons)