You've just finished a big, hearty meal, but instead of feeling full and satisfied, you crave something extra. It's not meat or vegetables you yearn for, however — it's sweets.
Why do people often hunger for sugary foods, even after an extravagant, 5-course meal? While there are several ideas, no one has definitively answered that question.
Some nutritionists claim people have been trained since childhood to expect a sugary dessert after a meal. And in many families, it's a time-honored tradition (and a way to bribe kids into finishing their broccoli).
Others claim human brain chemistry is to blame for an after-dinner sweet tooth. Some evidence suggests that consuming sugar (or other simple carbohydrates) can enhance the absorption of the amino acid tryptophan found in some foods. The tryptophan then enables an increase in the levels of serotonin, a neurotransmitter associated with feelings of well-being.
For some people, a heavy meal can result in a condition called postprandial (after a meal) or reactive hypoglycemia, a state of low blood sugar that's marked by hunger, weakness, sweating, shakiness, sleepiness, lightheadedness, anxiety or confusion, according to the National Institutes of Health. Consuming sweet foods is one way to counteract the symptoms of reactive hypoglycemia.
The condition usually occurs one to four hours after a meal that's rich in carbohydrates. Reactive hypoglycemia is especially common in people who've had gastric bypass surgery; they can easily experience "gastric dumping," the rapid movement of undigested food from the stomach into the small intestine.
The non-surgical causes of reactive hypoglycemia are somewhat mysterious. Scientists have studied several potential causes, including digestive enzyme deficiencies, low levels of the hormone glucagon and sensitivity to the hormone epinephrine.
To combat reactive hypoglycemia, doctors recommend eating smaller meals and avoiding heavy, carbohydrate-rich meals; eating a balanced, varied, high-fiber diet; and getting plenty of regular physical activity.
Contact Marc Lallanilla at email@example.com. Follow him on Twitter @MarcLallanilla. Follow LiveScience on Twitter @livescience. We're also on Facebook & Google+.