Pectin

Medlars contain plenty of pectin.

Gut bacteria break down soluble fiber, which includes pectin from apples, berries and citrus, into short chain fatty acids. Marsland says the fatty acids interact with spongy tissue inside the bones, where protective immune cells are produced, and help quiet immune system overactivity. An overzealous immune reaction can lead to inflammation.

Apple is rich in pectin and so is often added to other fruits when making jam so it will set.