I find that when I eat lunch I can feel myself instantly get tired as if a wave passes through me. My face gets a feeling of being sweaty and flushed. Coffee and copious amounts of water help counteract this. Also, it doesn't happen every day with every meal. Very small amounts of food don't cause this. It's as if I eat above a small threshold, then it happens. It makes it hard to work. A short nap would be perfect (but not possible). Is this something to be worried about?
The symptoms you describe sound like what many people call the "food coma." Sometimes, after eating a holiday meal, a big dinner or lunch, or even sometimes after meals that didn't seem that big, you may feel a bit drowsy. Some medical conditions can cause this feeling, including anemia, kidney dysfunction, sleep disorders, infections, or an electrolyte imbalance just to name a few. But even people who don't have any of these medical conditions may still feel tired after eating, because this symptom is also a consequence of normal digestion!
Why? Because our bodies spend a lot of energy digesting food. The stomach mechanically churns the food, produces acid to break the food into tiny pieces, and then controls the rate this broken down food can enter the intestines. In the intestines, enzymes use energy to further break down and absorb food particles into the body. For humans, it is normal for the rate of energy use to increase by 25 to 50 percent after a meal. This increased bodily activity could contribute to your feeling flushed after eating.
One explanation for your drowsiness lies in one of the hormones released during digestion — cholecystokinin. Commonly referred to as CCK, this hormone helps make you feel full, but also activates the areas in the brain associated with sleep. So after eating, when CCK levels rise to tell you you're full, you may also start to feel sleepy. Additionally, meals high in carbohydrates can increase the levels of tryptophan (an amino acid) in the blood. In the brain, tryptophan is converted into serotonin (a neurotransmitter that makes people feel both happy and sleepy). This boost in serotonin could also cause someone to feel tired.
Since you don't feel tired after every meal, you may want to keep a food journal to see what types of food have you craving a post-lunch nap. If carbohydrate-rich or heavy foods like pizza, pasta, or panini slow you down, you could opt for a salad, soup, or sushi on days when you have a lot of work to do in the afternoon. You could also try eating several smaller meals throughout the day, rather than a big lunch, to avoid overwhelming your digestive system.
Feeling tired after eating is a common experience, and not necessarily linked to a medical condition. However, if you feel your symptoms may be related to a medical problem, it's always a good idea to visit your health care provider, especially if your fatigue begins to seriously impair your ability to get your work done.
Best of luck in staying alert during your post-meal endeavors,Alice!