We all have been there. It’s lunchtime and you’re hungry. You munch on a sandwich or slurp some soup and maybe have a cookie if you’re craving sweets. Then, within about an hour comes payback. You start feeling slow, sluggish and sleepy. It’s hard to stay focused and pay attention, especially if you’re doing cognitive tasks such as learning, reasoning or solving problems. A nap feels like a great idea, but you aren’t necessarily able to take one.
Colloquially, that post-lunch afternoon slump is known as a food coma. Scientists call it “postprandial somnolence” or “postprandial dip” where the term postprandial refers to something that occurs after eating and somnolence means sleep. In science literature, postprandial somnolence is described as a feeling of tiredness observed after consuming a meal. Medical research suggests that the effects of the postprandial dip peak approximately thirty to sixty minutes after meals. During postprandial dips individuals experience reduced alertness, which affects their ability to concentrate and perform cognitive tasks. It’s a commonly cited reason for the mid-afternoon sleepiness, worldwide. Just about anyone regardless of their age, profession or geographical location had experienced it.
Food comas are generally viewed as a nuisance, but because they reduce the ability to concentrate, they can affect students’ performance—particularly on tests administered shortly after lunch. And that is an important issue. Standardized tests on language, math, and analytical reasoning have become indispensable tools for assessing children’s cognitive capacities worldwide (and especially in low- and middle-income countries where reliable data on children’s learning levels often remain unavailable.) The credibility of these tests relies on the assumption that testing conditions, test contents, and scoring procedures are identical for all test-takers. That’s what makes standardized tests globally trusted to give unbiased representations of cognitive skills.
In our study, which we had the opportunity to conduct in India—because of the prior ongoing research already in progress—we analyzed data from 4,600 Indian adolescents and young adults who took tests shortly after eating. Our findings suggest that food comas can considerably decrease test-takers cognitive skills.
A Look at Meal Timing and Test Results
Students who took tests less than an hour after their last meals performed significantly worse than individuals who tested more than an hour after eating. Specifically, compared to individuals who took the exams more than an hour after they last ate, those who took the exams within an hour of eating scored 8 percent lower in native and English languages and math tests. They also scored 5 percent lower in oral comprehension tests and 17 percent lower on fluid intelligence—the ability to reason quickly, adapt to new situations, and think on your feet.
Additionally, students who took tests less than an hour after meals reported 13 percent higher levels of fatigue than those who tested more than an hour after meals. We also found that the effect of postprandial testing varied by task difficulty. The negative effects of postprandial testing on cognitive performance were much stronger when test questions were more challenging. Testing within an hour after a meal decreased measured native-language reading proficiency by 18 percent for paragraphs, 7 percent for sentences, and 4 percent for individual words. We observed similar patterns on the math test.
Interestingly, no prior study considered the postprandial dip as a source of fatigue that can significantly alter individuals’ cognitive functioning. We hope that it helps draw more research to this common phenomenon, the causes of which are still not well-understood. For a long time, it was believed people felt sleepy because the blood flows were redirected away from the brain after meals. However, this view has now changed as newer evidence suggested that post-meal fatigue might be caused by the release of melatonin, the sleep hormone, and activation of the sleep centers in the brain. Indeed, it appears that some nerve pathways that play a role in digestion are similar to those involved in sleep. When these neural routes are activated after eating, individuals might start feeling drowsy.
So it’s not that food makes you lazier or unwilling to work hard enough. You’re still making an effort and trying to do your best, but your brain is just too foggy, and you aren’t able to process things as well as you normally would.
Our results suggest that food coma is a significant cause of reduced alertness and cognitive fatigue that inhibits students’ performance on tests across language, mathematics, fluid intelligence, and oral comprehension tests. Our study also raises a question whether tests taken post-lunch are an objective way to assess students’ cognitive skills. Finally, our results suggest that introducing naps into students’ academic schedule could improve their performance on tests. Notably, in China, naps are a common practice for students in schools. More recently, in Spain there was a debate about continuous versus split school days; the latter would allow children to nap. Our findings suggest that split days might help students recover from postprandial fatigue.
Changing school policies will undoubtedly take a while. However, in the meantime, parents and teachers can do a few things to reduce food coma effects. Research finds that meal sizes and compositions play a role too. For example, studies found that larger meals result in stronger food comas. Other studies found that foods high in fat, sugar or carbohydratesworsen post-meal fatigue. Avoiding these pitfalls will help minimize the afternoon slump.
There are ways to make this happen. For example, parents may have conversations with children about what foods make them sleepy versus not and suggest choosing items that don’t make them sleepy. On their part, teachers may remind students to avoid having a big lunch before an afternoon test, especially a high-stake one. Making smarter food choices will make students look as smart on tests as they actually are.
Justine Hervé is a professor of economics at Stevens Institute of Technology in Hoboken.
Get the latest on the best things to do with your family in and around New Jersey by signing up for our newsletter and following us on Pinterest, Facebook and Instagram!
Read More:
How to Spot the Signs of an Eating Disorder in Your Teen—and What to Do Next
I’m Pro-Vaccine, Pro-Science, and Still Asking the Hard Questions About Autism
Popular Now:
These NJ High Schools Send the Most Grads to Harvard, Princeton & MIT
This NJ Gem Was Just Named One of the Best New Hotels on the Planet
The Country’s Best Boardwalk is in New Jersey, According to USA Today Readers
Yes You Can Tour a 9,000-Square-Foot Chester Estate at Mansion in May
The Best High Schools for Athletes in New Jersey, According to a 2025 Ranking
