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.
Scientists 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 researchers were able to determine how long it took for their stomachs to empty. From 190 experiments, the average emptying time was 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. Newer results have shown 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.
The US Food and Drug Administration incorporates these data, standards and thousands of drug-food studies into actionable recommendations. The F.D.A. defines an empty stomach as “one hour before eating, or two hours after eating.” The F.D.A.’s two-hour rule is just a rule of thumb; the stomach will probably not be completely empty.
