Low blood sugar influences food cravings and increases the desire to eat unhealthy foods, especially in obese people, a new study suggests.

Researchers at the University of Southern California's Keck School of Medicine and Yale University studied lean and obese individuals after they were given insulin to reduce their blood sugar.

Researchers used functional magnetic resonance imaging to see which areas of the brain were activated when they looked at food images.

The food images ranged from cake to salad.

Participants had to rate their preferences, and results showed that all participants preferred the fatty foods when their blood sugar levels were below normal.

The prefrontal cortex is the part of the brain that says 'Stop eating,' lead researcher Kathleen Page said in a statement. When blood sugar levels are low, that area of the brain is less activated.

This was especially true in the study's obese participants.

Obese individuals lacked prefrontal brain activation even when sugar levels were normal, Page said in a statement. We don't know if obesity changes the way the brain responds or if it responds this way because of obesity.

Researchers say that keeping blood sugar levels steady is important to avoid overeating.

Eating healthy food that maintains glucose levels is the key, Page said.

The research will appear in The Journal of Clinical Investigation.