Why do resistant starches qualify as part of dietary fiber in the context of gut microbiome nutrition?

• A. Because they are fully digested into glucose in the stomach and therefore serve as the primary caloric source for colonic cells directly.
• B. Because resistant starches are water-soluble vitamins produced by plants and do not undergo fermentation by microbes.
• C. Because they are always absorbed in the duodenum and then secreted into the colon via bile, which classifies them as fiber by definition.
• D. Because they resist digestion in the small intestine and reach the colon where microbes ferment them, qualifying them functionally as fiber.

Answer: (D)