Nutritionist Carrie Dennett debunks several “nutrition urban legends,” such as the (false) notion that you shouldn’t eat fruit on an empty stomach.

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On Nutrition

Should you eat fruit on an empty stomach? Should you keep your carbs separate from your proteins? These rumors keep getting recycled in a succession of fad diets. I fell for them 20 years ago, and I get asked about it today. They’ve become nutrition urban legends.

The idea is that if you eat fruit with other foods, the sugar in the fruit will cause all of the food in your stomach to ferment, rot or putrefy (pick your word). This allegedly causes weight gain, bloating, diarrhea, gas and a host of other health problems.

The “fruit on an empty stomach” myth is an offshoot of the larger myth that our bodies can’t digest certain food combinations. The most common version is that we shouldn’t eat foods high in carbohydrates in the same meal as foods high in proteins or fats. One frequent explanation is that protein, carbs and fat require different digestive enzymes. Another is that carbs are digested in an alkaline environment while proteins are digested in an acidic environment. Either way, the story goes, if you eat these foods in combination, they will “cancel each other out” and not be digested.

There is simply no science to support these ideas, despite the fact that proponents of food combining (or food segregation, really) speak in terms that sound scientific.

Fermentation happens when bacteria break down carbohydrates or protein. The highly acidic stomach environment is quite hostile to the bacteria we ingest with our food, killing most of them outright and preventing the reproduction and colonization necessary for fermentation to happen.

Now let’s look at carbs vs. protein. It’s true that most protein digestion happens in the acidic environment of your stomach, while most carbohydrate digestion happens in the alkaline environment of your small intestine. However, your stomach becomes acidic even when you eat carbs alone, because your stomach starts producing acid as soon as you anticipate eating, before you even take a bite.

Any food that’s in your stomach gets churned and mixed with your stomach acid, then released into your small intestine. This prompts your pancreas to secrete bicarbonate into the small intestine to neutralize the acid, along with each of the enzymes needed to digest protein, carbohydrates and fat. In other words, the body is prepared to get a mixed meal, which makes sense when you consider that many single foods — like beans, milk and dairy products, nuts and seeds — are combinations of protein, fat and carbohydrates.

Carbohydrates, fat and protein are digested the same way whether you eat them alone or not. What may vary is how fast your stomach empties. It’s true that if you eat a high-carb, low-fat, low-protein meal, your stomach will empty faster — but you’ll also get hungry sooner. To avoid spikes and crashes in your blood sugar — and your energy levels — mixed meals are the way to go. This does slow down digestion, in a good way, because it helps you stay satisfied longer after eating.

If poor food combining leads to poor digestion, then you would lose weight, not gain weight, because you aren’t extracting all the nutrients or calories. If food combining helps you lose weight, it’s mostly because this is just another variation of a restrictive diet. In people predisposed to eating disorders, this could become a real problem. There are better ways to improve your digestion, like eating slowly and mindfully and aiming to eat until you are satisfied, not stuffed.