Feeling tired after eating is usually not a cause for concern by itself. But feeling sleepy all the time may be a sign of diabetes. Learn why you get tired after you eat.

Feeling tired after eating can be perfectly normal if you've had certain foods or had a big meal.

Simply feeling tired after eating isn't usually a sign of diabetes (or other medical conditions), Heidi Quinn, RDN, a certified diabetes educator at Harvard's Joslin Diabetes Center, tells LIVESTRONG.com 2. However, "overall fatigue" might be, she says.

As it turns out, food, fatigue and diabetes are closely linked. Here's what you need to know.

Read more: 9 Surprising Reasons You're Tired All the Time

What Exactly Is Diabetes?

Diabetes is a metabolic disorder in which the body is unable to properly use glucose (or blood sugar), the body's main source of energy, according to the Cleveland Clinic 1. When you eat, your body metabolizes the carbohydrates in food into glucose. The hormone insulin then helps move the glucose out of the bloodstream and into the cells.

But people with diabetes either don't produce enough insulin (type 1 diabetes) or can't use insulin effectively (type 2 diabetes). This causes glucose to build up in their blood, resulting in high blood sugar.

Elevated blood sugar levels can also be a sign of prediabetes. Prediabetes occurs when blood sugar levels are higher than normal but not high enough to be considered diabetes 2. If left untreated, however, prediabetes can progress into type 2 diabetes, according to the Joslin Diabetes Center 2.

Read more: What to Know About Normal Blood Sugar Levels in Women

Other symptoms of low blood sugar include:

  • feeling hungry
  • shaky
  • dizzy
  • confused or irritable
  • according to the Hormone Health Network 3

If you regularly experience these symptoms after eating, see a doctor. Though rare, reactive hypoglycemia can be caused by a number of medical conditions, not just diabetes 4.

Other Causes of Sleepiness After Eating

What you eat could make you ready for a nap after a meal. Loading up on sugary foods can result in an energy crash, for example. According to the National Sleep Foundation, eating lots of sugar can reduce the activity of orexin cells, which help regulate wakefulness 67.

Tryptophan, found in turkey, is often cited as the cause of sleepiness after a Thanksgiving feast. Cheese, fish and other high-protein foods also contain the amino acid. Tryptophan tends to increase serotonin levels, one of the hormones involved in sleep, according to the Cleveland Clinic 5.

But, according to the National Sleep Foundation, tryptophan doesn't immediately make you sleepy 7. A more plausible cause of post-meal drowsiness? Meal size. "Tiredness after eating may just mean that a person ate too much," says Quinn.

Read more: 4 Reasons You're So Tired After a Workout and What to Do About It