While eating an apple a day may not necessarily keep the doctor away, they are still an excellent, healthy snack to have on hand. One reason why apples are such a great option is that they contain two different types of fiber.  Apples have both soluble and insoluble fiber—the former slows digestion and helps prevent loose stools, while the latter can help with constipation.¹

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[1] https://medlineplus.gov/ency/article/002136.htm