If you find yourself feeling drowsy by mid-day, your diet could be to blame. A new study suggests that your level of alertness during the day may be related to the type of food you eat.

Researchers from Penn State College of Medicine, Pennsylvania, found that higher fat consumption was associated with increased sleepiness during the day.

In contrast, higher carbohydrate intake was associated with increased alertness, while no link was found between protein consumption and alertness.

The findings were consistent, regardless of the subjects' gender, age, body mass index, total amount of sleep they were getting or their total calorie intake.

"Excessive daytime sleepiness and fatigue are very prevalent in the modern world and on the rise," says principal investigator Alexandros Vgontzas, MD, professor of psychiatry at the Penn State College of Medicine. "Increased fat consumption has an acute adverse effect on alertness of otherwise healthy, non-obese adults."