What type of diets reduce undigested substrate for bacteria to feed off?

• A. High-fiber diets
• B. Easily digestible, low-fat diets
• C. Raw meat diets
• D. Very high-fat diets

Answer: (B)

The key idea is that colonic bacteria feed on undigested substrates that reach the colon. If a diet is easily digested and absorbed in the small intestine, there’s less material left over for bacteria to ferment, so you reduce the fuel available to them. An easily digestible, low-fat diet fits this because it minimizes indigestible residue that would otherwise travel to the colon and serve as substrate for bacterial fermentation.

In contrast, a high-fiber diet increases the amount of undigested carbohydrate reaching the colon, boosting bacterial fermentation. A raw meat diet provides little carbohydrate, but it doesn’t specifically minimize all possible undigested substrates and has other considerations. Very high-fat diets don’t directly reduce the substrates bacteria feed on in the colon.