Researchers have discovered a mechanism that prompts people to seek food rich in glucose - the body's main energy source.
An enzyme called glucokinase in the brain, involved in sensing glucose in the liver and pancreas, plays a key role in driving our desire for glucose, reserachers showed in their findings.
It might be possible to reduce cravings for glucose by altering one's diet, it suggested.
"Our brains rely heavily on glucose for energy. So we have a deep-rooted preference for glucose-rich foods," said lead researcher James Gardiner from Imperial College London.
The researchers discovered that when rats go for 24 hours without eating, the activity of glucokinase in an appetite-regulating centre of the brain increases sharply.
The rats were given access to a glucose solution as well as their normal food pellets, called chow.
When the researchers increased the activity of glucokinase in the hypothalamus using a virus, rats consumed more glucose in preference to chow. When glucokinase activity was decreased, they consumed less glucose.
"This is the first time anyone has discovered a system in the brain that responds to a specific nutrient, rather than energy intake in general," Gardiner pointed out.
It suggests that when you are thinking about diet, you have to think about different nutrients not just count calories, Gardiner added.
The study appeared in the Journal of Clinical Investigation.