Why do I feel especially sleepy just before my 2 p.m. stats class? Sure the material may not be particularly enthralling, but it’s that post-lunch funk between 1 and 2 p.m. when many of us find ourselves desperately searching for a quick energy boost. Be it breakfast, lunch or dinner, after a heavy meal our brains become much less alert.

The increased level of blood and glucose that occurs after eating often results in lethargy. This concept may seem illogical at first, as it would seem this would supply more energy to the brain. However, studies have indicated the contrary. There is actually an increased amount of blood rushing to the stomach after a meal, to aid the breakdown and digestion of food. With more blood traveling to the stomach, less oxygen is supplied to the brain, which explains the inevitable bout of sleepiness.

This amount depends on the caloric intake and whether the ingested nutrients are carbohydrates, fat or protein. Therefore, the larger the meal, the more tired you feel. Keep in mind that different nutrients are digested at different times. Depending on your metabolism, about 20 minutes after a meal, carbohydrates are the first to be absorbed, followed by proteins, that take 25 minutes to an hour, and lastly, fats which range from three to five hours for digestion. According to dietitian Susan Zbornik, “the more fat you eat, the longer you will feel tired. Although you feel sluggish […] your body is actually working hard to handle all that food.”

There are a number of reactions set off in the brain in response to food, or a lack thereof. Conventionally, orexin proteins are produced by orexin neurons in the hypothalamus. These proteins help us stay awake during the day and become dormant at night. In a study conducted by Denis Burdakov of the University of Manchester, it was found that this neuron activity could be decreased by minute elevations in glucose from an average-sized meal. Orexin neuron activity is highest at low blood glucose levels, explaining why we cannot sleep when we are hungry.

“We think orexin neurons make sure that we are awake and alert when hungry, in order to ensure optimal food-seeking,” says Burdakov. “It makes evolutionary sense for animals to turn off their wakefulness and conserve energy once they have eaten their food, since it could be risky or wasteful to expend too much energy looking for more food.” Thus, it is believed that changes in orexin level can also affect eating patterns. Late-onset obesity could result if levels of orexin protein are too high over a long period of time.

So avoid reaching for a sugary snack when feeling the effects of a large meal, as tempting as it may be. While sugar does provide a quick boost of energy, the effect is short-lived and the resulting increased glucose level will ultimately leave you feeling more tired. In most cases, a moderate dose of caffeine will do the trick. Ulimately, the best method is prevention. Eating small, well-balanced meals throughout the day will help maintain energy levels and alertness.