According to experts, the belief that turkey causes a food coma during holiday feasts is largely a myth. While turkey does contain tryptophan, an amino acid that can contribute to the production of serotonin and melatonin, you would need to eat a massive amount of turkey - about eight pounds of it - to feel sleepy. Instead, things like overeating, the high carb content in holiday side dishes, changes in blood flow during digestion, and drinking alcohol are more likely to make us feel tired after a big meal. Ultimately, the food coma sensation is likely due to a combination of these factors rather than turkey alone.