The saying “an apple a day keeps the doctor away” may not be that far from the truth when it comes to treating the obesity epidemic. Researchers from Washington State University cut open an assortment of apples, took a closer look at its compounds, and published their findings in the journal Food Chemistry.

"We know that, in general, apples are a good source of these non-digestible compounds, but there are differences in varieties," the study's lead researcher Giuliana Noratto a food scientist at Washington State University said in a press release. But not all apples are made the same, and one apple in particular has more obesity fighting power than all the rest. "Results from this study will help consumers to discriminate between apple varieties that can aid in the fight against obesity."

After researchers examined the compounds in the Granny Smith, Braeburn, Fuji, Gala, Golden Delicious, McIntosh, and Red Delicious apples, they measured the non-digestible levels each type contained. The tart green Granny Smith apples contained the highest levels of non-digestible compounds, including dietary fibers, polyphenols, and a low content of available carbohydrates. Once digested, these bacteria-friendly compounds travel down to the colon intact, where they ferment and grow healthy bacteria in the gut and help improve digestion.

When a person is obese, they have a complete unbalanced colony of bacteria living inside their gut, and over a third of Americans are weighing into the obesity category today, according to the Centers for Disease Control and Prevention. It’s only in recent years that researchers have discovered the importance behind the billions of gut microbes that hide within our stomach and help break down our foods. There are good and bad bacteria, and the wrong mix can set the stage for obesity, diabetes, and a slew of other unwanted comorbidities, but eating a Granny Smith apple a day could put you back into balance.

Twin studies were the first indications that gut microbes had anything to do with obesity when obese and lean individuals’ insides were compared. Lean individuals had a wide variety of species within their gut community, but there was less diversity and excitement inside an obese person’s stomach. A diet in highly processed foods has been linked to less diverse guts, which is exactly why Granny Smith apples can help move the gut back into a healthier balance, make you feel satisfied, and according to Noratto, could also help with chronic inflammation, which can lead to diabetes and other metabolic disorders associated with obesity.

"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," Noratto said. "What determines the balance of bacteria in our colon is the food we consume."

Source: Condezo-Hoyos L, Mohanty IP, and Noratto GD. Assessing non-digestible compounds in apple cultivars and their potential as modulators of obese faecal microbiota in vitro. Food Chemistry. 2014.