Question:
Dietary fibers are degraded by colonic bacteria to form which of the following?
Dietary fibers are degraded by colonic bacteria to form which of the following?
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Colonic bacteria ferment fiber into short-chain fatty acids; butyrate feeds the colon cells.
Updated On: Jul 8, 2026
- Butyrates
- Glycerol
- Sucrose
- Free radicals
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Question.
Dietary fiber (mostly non-starch polysaccharides like cellulose, hemicellulose, and pectin) cannot be digested by human enzymes in the small intestine. The question asks what colonic bacteria turn this fiber into once it reaches the large bowel.
Step 2: Recall what colonic bacteria do to fiber.
Bacteria in the colon ferment undigested fiber without oxygen. This fermentation breaks the long fiber chains down into short-chain fatty acids (SCFAs), mainly acetate, propionate, and butyrate, along with gases like hydrogen, methane, and carbon dioxide.
Step 3: Focus on butyrate.
Butyrate is the SCFA that matters most for the colon itself. Colonocytes (the cells lining the large intestine) use butyrate as their main fuel, ahead of glucose. Butyrate also helps keep the colon lining healthy and is linked to lower colon cancer risk.
Step 4: Rule out the other options.
(B) Glycerol: Glycerol comes from fat breakdown, not from fiber fermentation. Incorrect.
(C) Sucrose: Sucrose is a simple sugar absorbed in the small intestine; it is not a fermentation product of fiber. Incorrect.
(D) Free radicals: Free radicals are reactive oxygen species from oxidative processes, not a normal fermentation output of colonic bacteria. Incorrect.
Step 5: Final Answer.
Colonic bacterial fermentation of dietary fiber mainly yields short-chain fatty acids, of which butyrate is the key one used by colon cells.
\[ \boxed{\text{Butyrates}} \]
Dietary fiber (mostly non-starch polysaccharides like cellulose, hemicellulose, and pectin) cannot be digested by human enzymes in the small intestine. The question asks what colonic bacteria turn this fiber into once it reaches the large bowel.
Step 2: Recall what colonic bacteria do to fiber.
Bacteria in the colon ferment undigested fiber without oxygen. This fermentation breaks the long fiber chains down into short-chain fatty acids (SCFAs), mainly acetate, propionate, and butyrate, along with gases like hydrogen, methane, and carbon dioxide.
Step 3: Focus on butyrate.
Butyrate is the SCFA that matters most for the colon itself. Colonocytes (the cells lining the large intestine) use butyrate as their main fuel, ahead of glucose. Butyrate also helps keep the colon lining healthy and is linked to lower colon cancer risk.
Step 4: Rule out the other options.
(B) Glycerol: Glycerol comes from fat breakdown, not from fiber fermentation. Incorrect.
(C) Sucrose: Sucrose is a simple sugar absorbed in the small intestine; it is not a fermentation product of fiber. Incorrect.
(D) Free radicals: Free radicals are reactive oxygen species from oxidative processes, not a normal fermentation output of colonic bacteria. Incorrect.
Step 5: Final Answer.
Colonic bacterial fermentation of dietary fiber mainly yields short-chain fatty acids, of which butyrate is the key one used by colon cells.
\[ \boxed{\text{Butyrates}} \]
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