Glucose is a component of carbohydrates, and the main energy source used by brain cells.
By studying rats, a team at Imperial College London identified a mechanism that appears to sense how much glucose is reaching the brain, and prompts animals to seek more if it detects a shortfall.
The researchers believe it may play a role in driving our preference for sweet and starchy foods.
Dr James Gardiner, from the Department of Medicine, who led the study, said: "Our brains rely heavily on glucose for energy. It's clearly a very important nutrient, but in our evolutionary past it would have been hard to come by. So we have a deep-rooted preference for glucose-rich foods and seek them out."
The researchers hypothesised that an enzyme called glucokinase might play a role in driving our desire for glucose. Glucokinase is involved in sensing glucose in the liver and pancreas. It is present in the hypothalamus, an area of the brain that regulates a variety of essential functions including food intake, but its exact role was unclear.
"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. It suggests that when you're thinking about diet, you have to think about different nutrients, not just count calories," Dr Gardiner said.