Fruit is an incredibly healthy food group that's packed with vitamins, nutrients, fiber, and water. But there have been some nutritional claims circulating that suggest fruit can also be damaging if eaten in conjunction with other foods. The basic premise is that high-sugar fruits help to ferment the other digested foods in a "full" stomach, causing gas, indigestion, and other problems. While it's true that fruit helps accelerate fermentation in things such as bread starters, the idea that it could do so in a stomach is completely false.
"There is no need to eat any food or type of food on an empty stomach. This myth has been around for a long time. There is no science to support it even though proponents make scientific-sounding statements," Jill Weisenberger, MS, RD, CDE, author of Diabetes Weight Loss—Week by Week, told HuffPost Healthy Living by email.
Fermentation is a process that requires bacteria, fed by sugars, to colonize on food, and change its composition (examples of fermented foods include wine, yogurt, and kombucha). But stomachs, with their high concentrations of hydrochloric acid, are hostile environments that kill bacteria far before they are able to colonize and reproduce.
"One of the main purposes of the stomach is to sterilize food by mixing and churning it within the muscular, acid-containing stomach,” Dr. Mark Pochapin, director of the Monahan Center for Gastrointestinal Health at NewYork-Presbyterian Hospital/Weill Cornell Medical Center told the New York Times in an article on the topic.
A similar claim that the body has trouble digesting the carbohydrates in fruit in combination with other foods is also not supported by the science. "The body produces digestive enzymes for protein, fat, and carbohydrates and releases them from the pancreas together," says Weisenberger. "If we could not digest mixed meals, we would not even be able to digest most foods since most foods are a combination of nutrients. Even vegetables like green beans and broccoli are a mix of carbohydrate and protein."
What's more, gas is produced by the colon—not the stomach. So while fruit can cause gas in some people, the contents of their stomachs will have little relevance. However, food reaches the colon about six to 10 hours after we eat it. So while fruit isn't damaging to eat at any time, it is true that we spend many hours digesting it anyway.
Ultimately, the better question is how much—rather than when—should we eat healthful foods like fruit.
"The concern should not be, 'Should I eat this on an empty stomach or with a meal?' Weisenberger says. "Rather the concern should be, 'How can I eat more of this health-boosting food group?'"