Which nutrient passes through the GI tract mostly undigested and unabsorbed?

Question

BlackTom AI · Accepted Answer

Dietary fiber is largely resistant to human digestive enzymes, so it passes through the gastrointestinal tract mostly undigested and unabsorbed.

1) Relevant knowledge points and concepts
- Major macronutrients (carbohydrate, protein, fat) are broken down by specific enzymes in the GI tract and absorbed primarily in the small intestine. Carbohydrates → monosaccharides (amylase, disaccharidases); proteins → amino acids/di‑/tripeptides (pepsin, pancreatic proteases, brush‑border peptidases); fats → free fatty acids/monoglycerides (lipase, bile emulsification), packaged into micelles and chylomicrons for absorption.
- Dietary fiber (cellulose, hemicellulose, pectin, lignin) contains β‑glycosidic bonds and structures human enzymes cannot hydrolyze. Fiber includes insoluble types (add bulk, speed transit) and soluble types (can be partially fermented by colonic bacteria).
- Colonic bacteria ferment some soluble fiber to short‑chain fatty acids (SCFAs), which can be absorbed, but the bulk of fiber remains unabsorbed and is excreted.

2) Step‑by‑step reasoning
- Ask: which nutrient is NOT digested/absorbed? Examine each option:
  a. Fat: emulsified by bile, hydrolyzed by pancreatic lipase, absorbed as fatty acids/monoglycerides → absorbed (so not correct).
  b. Fibre: human digestive enzymes cannot break its β‑linkages; it largely transits to the colon intact; only partial bacterial fermentation occurs → mostly undigested/unabsorbed (correct).
  c. Protein: denatured and hydrolyzed by pepsin and pancreatic proteases to absorbable amino acids → absorbed (not correct).
  d. Carbohydrate: starch is digested to glucose by amylases and disaccharidases and absorbed via SGLT1/GLUT transporters → absorbed (not correct).

3) Intermediate/auxiliary details
- Although soluble fiber yields some SCFAs upon fermentation (providing small energy and local effects), this does not equal the digestion and absorption seen with fats, proteins, and digestible carbohydrates.

4) Why the correct answer is correct
- Fiber’s chemical bonds are resistant to human digestive enzymes, so it largely remains undigested and unabsorbed, fitting the question’s criterion.

5) Why other options are incorrect
- Fat, protein, and carbohydrate are primarily digested and absorbed in the small intestine via established enzymatic and transport processes.

Conclusion: The correct answer is b. fibre, which matches the provided answer.

Which nutrient passes through the GI tract mostly undigested and unabsorbed?单项选择题

类似问题

What does the fiber in diet pills do?

Fiber that is generally non-viscous and non-fermentable falls under what category of fiber?

Which of the foods below does not contain dietary fiber?

Gums are classified as soluble fiber because they are not completely digested/absorbed by the body. What is a consequence?

A very active 24-year-old male consumes 4,000 kcal/day. Based on his current energy intake, he should get an average of _____ grams/day of total dietary fiber.

Which statement is FALSE? Excessive dietary fiber intake in young children is a potential health concern because:

Which of the following health concerns could be from eating a low fiber diet?

A student consumes 2000 calories a day and usually consumes 10 grams of fiber. How much fiber do they need to add to their diet to meet the fiber recommendations?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单