Grab your basket and get thee to your nearest U-Pick-Em. There’s a great new reason to embrace apple picking. A study released this week from Washington State University has found that apples can fight obesity.The fruit’s combination of nondigestible fiber, polyphenols and low levels of available carbohydrates, the researchers determined, benefits the growth of good bacteria in the gut that support healthy weight and metabolism. These nondigestible compounds actually changed the proportions of fecal bacteria (a reflection of gut bacteria) in mice used for the study. The result was that the poop of obese mice ended up looking similar, bacteria-wise, to that of lean mice, according to food scientist Giuliana Noratto, the lead study author.Which apples should you pick when you pick? Noratto’s team compared the effects on gut flora of seven types of apples and found that tart Granny Smiths have a leg-up on keeping you trim. They were higher in the crucial compounds than Braeburns, Fujis, Galas, Golden Delicious, McIntosh and Red Delicious.“What determines the balance of bacteria in our colon is the food we consume,” says Noratto. So follow the old adage and grab a Granny Smith today.MORE: Skinny People’s Poop Could Cure Obesity