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Ask Well
Two hours after eating is a crude rule of thumb. A more accurate answer depends on the drugs you are taking and your medical conditions.
By Richard Klasco, M.D.
Q. Many medications should be taken on an empty stomach. How do you know when your stomach is empty?
A. Two hours after eating is a crude rule of thumb. A more accurate answer depends on the drugs you are taking and your medical conditions.
Doctors began studying gastric emptying times in the 1940s at Guy’s Hospital in London. Gastric emptying time is the length of time required for the stomach to return to empty after a meal.
In 1951, they published findings on 21 volunteers. Each subject ingested a test meal of gruel. Then, the contents of their stomachs were sucked back out. By repeating the experiment at various time points, the doctors were able to determine how long it took for their stomachs to empty. From 190 experiments, the doctors calculated the average emptying time to be about two-and-a-quarter hours.
In 1966, other investigators began using radioactive substances to measure gastric emptying. With refinements over the years, this technique has become the standard for assessing the rate of gastric emptying.
Standards for such testing have been set by the American Neurogastroenterology and Motility Society and the Society of Nuclear Medicine. They state that a normal stomach should be 90 percent empty after four hours. The difference between this standard and the earlier study probably reflects differences in foods. Solids take longer to digest than liquids; fats take longer to digest than protein or carbohydrates.
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