Uploaded December 2024 | Updated September 2026, 2 weeks ago
I have a very large class, about 800 students and exams are online. The exam has a time limit but it can be taken at any time on the given day. Some take it earlier in the day, some later. That presents me with an opportunity to do a study of what is colloquially called “food coma” or scientifically, “postprandial somnolence.” We have all experienced this sometime. It is a feeling of lethargy that happens after a heavy meal such as a holiday turkey feast. A common explanation that has been proposed for this is that turkey contains a lot of the amino acid tryptophan that in the body is first converted to serotonin and then to melatonin which induces sleepiness. Sounds plausible but it doesn’t stand up to scrutiny. Chicken has just as much tryptophan and salmon has more ,but nobody talks about a salmon meal inducing sleep. Another explanation is that digestion requires a great deal of energy, diverting energy from other activities.
Whatever the reason, it is clear that postprandial sluggishness is real. It has even been demonstrated in California sea slugs! These little guys feed on seaweed and their activity after meals has been monitored and they certainly slow down. As you can imagine videoing sea slug activity is not the most thrilling research, but it seems there is no question they do become even more sluggish after feasting on seaweed. Researchers showed that this slowing down is associated with more neurotransmitter activity that signals memory enhancement. They hypothesize that this is an evolutionary phenomenon so that they can better remember where their scrumptious meal came from. Somewhat of a stretch, I think.
Meals also induce sleep in fruit flies. Yes, that has actually been studied. Individual flies are constrained in tubes so that their activity can be monitored, and they do indeed go to sleep after dining. Of course, in most cases the human brain is a lot more sophisticated than that of a fruit fly, so it is hard to know what to make of this research. But there have been studies of “food coma” in humans and one actually did furnish some useful information. About 4600 adolescents and young adults in India were administered comprehension and math tests by monitors who came to their homes at different times of the day without previous announcement. Results showed that test scores were reduced by about 10% if the test was taken within an hour of having had a meal. The effect of food coma was worse when the tests were more difficult.
The take-away message would seem to be that your last meal should be at least an hour before engaging in a mental task. There was one other intriguing study that showed that a cash incentive at the times of tests increases performance by 13%. But it has to be a significant amount. If only a small reward is offered, students do more poorly than when there is no compensation. I don’t think I would get university approval to confirm that result but I will be able to ask students about the time of day they start my exam relative to a meal and we will see if any interesting data emerges.
I have a very large class, about 800 students and exams are online. The exam has a time limit but it can be taken at any time on the given day. Some take it earlier in the day, some later. That presents me with an opportunity to do a study of what is colloquially called “food coma” or scientifically, “postprandial somnolence.” We have all experienced this sometime. It is a feeling of lethargy that happens after a heavy meal such as a holiday turkey feast. A common explanation that has been proposed for this is that turkey contains a lot of the amino acid tryptophan that in the body is first converted to serotonin and then to melatonin which induces sleepiness. Sounds plausible but it doesn’t stand up to scrutiny. Chicken has just as much tryptophan and salmon has more ,but nobody talks about a salmon meal inducing sleep. Another explanation is that digestion requires a great deal of energy, diverting energy from other activities.
Whatever the reason, it is clear that postprandial sluggishness is real. It has even been demonstrated in California sea slugs! These little guys feed on seaweed and their activity after meals has been monitored and they certainly slow down. As you can imagine videoing sea slug activity is not the most thrilling research, but it seems there is no question they do become even more sluggish after feasting on seaweed. Researchers showed that this slowing down is associated with more neurotransmitter activity that signals memory enhancement. They hypothesize that this is an evolutionary phenomenon so that they can better remember where their scrumptious meal came from. Somewhat of a stretch, I think.
Meals also induce sleep in fruit flies. Yes, that has actually been studied. Individual flies are constrained in tubes so that their activity can be monitored, and they do indeed go to sleep after dining. Of course, in most cases the human brain is a lot more sophisticated than that of a fruit fly, so it is hard to know what to make of this research. But there have been studies of “food coma” in humans and one actually did furnish some useful information. About 4600 adolescents and young adults in India were administered comprehension and math tests by monitors who came to their homes at different times of the day without previous announcement. Results showed that test scores were reduced by about 10% if the test was taken within an hour of having had a meal. The effect of food coma was worse when the tests were more difficult.
The take-away message would seem to be that your last meal should be at least an hour before engaging in a mental task. There was one other intriguing study that showed that a cash incentive at the times of tests increases performance by 13%. But it has to be a significant amount. If only a small reward is offered, students do more poorly than when there is no compensation. I don’t think I would get university approval to confirm that result but I will be able to ask students about the time of day they start my exam relative to a meal and we will see if any interesting data emerges.
