You’ve heard the old adage, “An apple a day keeps the doctor away,” but never has it rung more true than it does now. According to researchers from Washington State University, Granny Smith apples act as a prebiotic in the gut, altering the bacteria in obese individuals to be more like those found in lean individuals. Their study, published recently in the journal Food Chemistry, highlight the beneficial effects of the apples on gut bacteria.

Apples are a good source of fiber. Different varieties of apple carry different amounts of fiber and other compounds. Granny Smith apples are high in fiber and polyphenols, and are lower in available carbohydrates than other, sweeter apples. These properties make it particularly beneficial to the gut bacteria.

“The non-digestible compounds in the Granny Smith apples actually changed the proportions of fecal bacteria from obese mice to be similar to that of lean mice,” noted Giuliana Noratto, PhD, the study’s lead researcher.

In the study, the researchers tested the effects of Braeburn, Fuji, Gala, Golden Delicious, McIntosh, and Red Delicious apples on the gut bacteria of obese mice, and compared it with the gut bacteria of lean mice. The Granny Smith apples had the highest amount of non-digestible compounds and outperformed the other apples when it came to altering gut bacteria levels in the obese mice.

The effect our gut microbes have on our health—particularly when it comes to weight gain and obesity—is amazing. It’s the topic of my new book, The Skinny Gut Diet, and a topic Dr. Smith and I have covered many times on this blog. I love Granny Smith apples. They are lower in sugar than other apples, and so they make a great snack. Spreading almond butter on half a Granny Smith apple is the perfect snack—and it just got even better with the results of this study.