OJ on an empty stomach may not be so great
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Orange juice is a breakfast staple. If your continental breakfast doesn’t come with a glass, you’ll probably want to change continents. But next time you start your day with a glass of orange juice (or any sugary beverage for that matter), you may want to save it for the end of the meal: Turns out that chugging fructose on an empty stomach might be playing havoc with your liver and gut health.

According to a new paper from researchers at Princeton University and published in the journal Cell Metabolism, a study conducted on mice found that fructose, which is fruit sugar, is processed mainly in the small intestine instead of the liver as previously thought. If fructose is not processed in the small intestine, it then moves on to the liver or the large intestine and colon. For the liver, previous studies have shown that excessive amounts of sugar can cause damage. And now, knowing that this excess fructose is also going to the microbiome in the small intestine and colon, researchers suggest that it could be having an effect there too—though exactly how they are still not sure.

As a result, the authors suggest keeping sugar intake, including fructose intake, at reasonable levels. “There is a fundamental physiological difference in how smaller and larger amounts of sugar are processed in the body,” Joshua D. Rabinowitz of the Lewis-Sigler Institute for Integrative Genomics at Princeton University, whose laboratory led the study, said in a statement. “The prior view was that the liver processes all ingested sugar. But this study showed that more than 90 percent of the fructose was cleared by the small intestine in mice.”

With that in mind, Rabinowitz suggested consuming only “moderate amounts” of fructose to keep it from reaching the liver. However, he also stated that just a can of soda or a large glass of orange was probably about twice as much as he would consider “moderate.”

Additionally, the researchers found that the small intestine is better at processing fructose after a meal. As a result, the authors postulate that drinking fruit juices on an empty stomach—such as the classic example as having a glass of OJ first thing in the morning—can negatively affect your health. “The microbiome is designed to never see sugar,” Rabinowitz continued, essentially implying that any amount of fructose reaching your large intestine could be problematic. “As soon as you drink the soda or juice, the microbiome is seeing an extremely powerful nutrient that it was designed to never see.”

Again, the researchers stressed that their study didn’t explicitly show that fructose impacts the microbiome. However, the believe that an effect is “likely,” and it should be studied further. In the meantime, Rabinowitz suggested “the most old-fashioned advice in the world”: cut back on sugar overall, but if you must indulge, save it for after a meal.