There may be some truth to the old apple-a-day adage. It might not only keep the doc at bay but could help you drop pounds as well.

A study published in the journal Food Chemistry found that nondigestible compounds in apples can help fight obesity — as well as disorders related to it, like diabetes, heart disease and stroke — and that Granny Smiths, containing the most weight loss compounds, were the clear winner in the apple category.

Granny Smith apples promote the growth of good bacteria in the colon because of their high content of nondigestible compounds, like dietary fiber and polyphenols, and a low amount of carbohydrates.

When you chew and eat a Granny Smith, the compounds reach the colon, where they ferment and grow friendly bacteria colonies there.

Scientists know that obese people have an imbalance in their colons’ bacterial communities, which leads to inflammation and triggers disorders like diabetes. The compounds in green apples can help restore this balance and prevent some of the damage of obesity.

Granny Smiths won out over Braeburn, Fuji, Gala, Golden Delicious, McIntosh and Red Delicious varieties.

“The nondigestible compounds in the Granny Smith apples actually changed the proportions of fecal bacteria from obese mice to be similar to that of lean mice,” said Giuliana Noratto, a food scientist and the lead researcher of the study.

Granny Smiths have always been a sound addition to any weight loss plan, because they’re high in fiber, low in calories (just 80 for a medium apple) and easily fill you up. The soft inside part of the apple contains soluble fiber, which attracts water to the intestine, slowing digestion and forcing food to stay in your stomach. That causes you to feel fuller longer, which helps keep you from eating more. But now that the tart apple actually changes colon bacteria that can reduce your risk of obesity, apples may just be the new, old health food.

Try these tasty ways to eat more Granny Smith apples:

  • Bite into the Granny Smith raw.
  • Toss diced Granny Smiths into salad, oatmeal or stir fry.
  • Caramelize Granny Smith wedges with 2 tablespoons of butter in a pan until softened and browned, add a sprinkling of cinnamon and top plain or frozen yogurt.
  • Add sliced apple to grilled cheese sandwiches.
  • Toss one shredded apple into coleslaw for a hint of sweet tartness.
  • Chop peeled apple and add to fruit smoothies.
  • Make a baked apple breakfast. Core a Granny Smith to within an inch of the bottom, creating a pocket. Fill the pocket with a tablespoon each of raisins and old fashioned oats and a sprinkling of cinnamon. Place in a baking dish lined with foil, pour ¼ cup of water around the apple and turn up foil edges to form a cup. Top the apple with a pat of butter and bake at 350 degrees for 30 to 35 minutes, until soft.