What if you don't eat what will happen to your

“The main fuel for your brain is glucose, which you get from eating foods—predominantly carb-rich ones,” Rachele Pojednic, Ph.D., assistant professor in the nutrition department at Simmons College and professor at the Harvard Extension School, tells SELF. Complex carbohydrates, like fruits, vegetables, and whole grains, are the most nutritious sources of glucose because they take a longer time to digest than refined carbs (plus they’re often loaded with other beneficial nutrients). Without a frequent carb supply, your blood sugar can dip too low, leaving you feeling sluggish, irritated, and like you can’t concentrate, says Zeitlin.