We've all been there.

After a very heavy meal, like Christmas dinner, you can sometimes be very sleepy. It's what some people call a food coma. Well, it turns out there is a specific reason why this happens. Researchers in Scripps Research Institute Florida used fruit flies to test the effects that food has on someone/something. Associate Professor William Ja said, “Different foods play different roles in mammalian physiology, but there have been very few studies on the immediate effects of eating on sleep." To investigate the idea of food affecting sleep they created a system called the "Activity Recording CAFE (ARC)", which consisted of a plastic chamber which was used to record fly activity before and after eating. They found that flies slept for a short period after eating and then woke up to carry on as normal. Their sleep time and response depended on the type of food and the amount they ate. The study found that protein, salt and the amount eaten meant more sleep but sugar had no effect. William stated, “The protein link to post-meal sleep has been mostly anecdotal, so to have it turn up in the study was remarkable. In humans, high sugar consumption provides a quick boost to blood glucose followed by a crash, so its effect on sleep might only be observed beyond the 20 to 40 minute food coma window.” They've concluded that the reason for this 'food coma' could be a way for someone/something to to maximize gut absorption of nutrients. For flies this was protein and salt because those two nutrients are limited in nature. It will vary with humans, depending on what type of nutrients they want to absorb. William added, “Using an animal model, we’ve learned there is something to the food coma effect, and we can now start to study the direct relationship between food and sleep in earnest. This behavior seems conserved across species, so it must be valuable to animals for some reason."