Chapter 3 — Quiz

Twenty questions. Attempt before opening.

Multiple Choice

1. Essentially all nutrient absorption occurs in the:

  • a) Stomach
  • b) Small intestine
  • c) Large intestine
  • d) Liver
Answer **b.** The stomach absorbs almost nothing (a little water, some alcohol, a few drugs). The large intestine absorbs water, electrolytes, and short-chain fatty acids. The liver isn't part of the tube.

2. Bile is best described as:

  • a) An enzyme that breaks down fat
  • b) A detergent that emulsifies fat, increasing surface area for enzymes
  • c) A hormone released by the gallbladder
  • d) A waste product excreted into the gut
Answer **b.** Bile does no chemical breakdown itself. It breaks large fat droplets into a fine emulsion — exactly what dish soap does to grease — so that pancreatic lipase has enough surface to work on.

3. Lactose intolerance occurs because:

  • a) The immune system attacks lactose
  • b) The stomach lacks acid to break down milk
  • c) Brush-border lactase production declines, so lactose reaches the colon and is fermented
  • d) The pancreas stops producing lactase
Answer **c.** Lactase is anchored to the microvilli of the intestinal cells. Without it, lactose isn't split, so it isn't absorbed; it travels to the colon where bacteria ferment it, producing gas and drawing in water. Not an allergy (a), and not pancreatic (d).

4. Vitamin B12 absorption requires:

  • a) Bile from the gallbladder
  • b) Intrinsic factor from the stomach, and an intact ileum
  • c) Pancreatic amylase
  • d) An acidic environment in the small intestine
Answer **b.** Two separate requirements in two separate places — which is why stomach surgery, autoimmune parietal cell damage, long-term acid suppression, *or* ileal resection can each independently cause B12 deficiency regardless of dietary intake.

5. Long-chain dietary fat differs from glucose and amino acids in that it:

  • a) Is absorbed in the stomach
  • b) Enters the lymphatic system as chylomicrons, bypassing the liver's first pass
  • c) Cannot be absorbed without bacterial fermentation
  • d) Is absorbed in the colon
Answer **b.** Carbohydrate and protein go via the portal vein straight to the liver. Long-chain fat is packaged into chylomicrons and enters via lymph, joining the bloodstream near the heart — reaching general circulation before the liver processes it.

6. Butyrate is notable because:

  • a) It's an essential fatty acid you must obtain from the diet
  • b) It's produced by bacterial fermentation of fiber and is the preferred fuel of colon cells
  • c) It's the main product of protein digestion
  • d) It's absorbed in the stomach
Answer **b.** Your gut lining is partly fed by your bacteria, from material you couldn't digest. This is the mechanistic core of why fiber matters.

7. Which hormone is released by the stomach and increases hunger?

  • a) CCK
  • b) GLP-1
  • c) Ghrelin
  • d) PYY
Answer **c.** Ghrelin — the main "start eating" signal. CCK, GLP-1, and PYY all point the other way.

8. GLP-1 receptor agonist medications are relevant to this chapter because they:

  • a) Prove that calories don't matter
  • b) Demonstrate at scale that gut hormone signalling is a major determinant of how much people eat
  • c) Work by blocking fat absorption in the small intestine
  • d) Replace intrinsic factor
Answer **b.** They mimic a gut hormone, slow gastric emptying, and reduce appetite. Whatever one thinks about them, they are large-scale evidence that appetite is substantially hormonal rather than purely volitional.

9. Whole almonds deliver less energy than their label states primarily because:

  • a) The label is fraudulent
  • b) Almonds contain no absorbable fat
  • c) Fat is locked inside intact plant cell walls that chewing doesn't fully rupture
  • d) Almonds are fermented in the colon rather than digested
Answer **c.** Structure, not chemistry. Grind them into butter and more energy becomes available — same molecules, different packaging.

10. The "detox" claim fails primarily because:

  • a) Toxins don't exist
  • b) The liver and kidneys perform continuous biotransformation and excretion, with no backlog, and the claimed toxins are never named or measured
  • c) Juice cannot enter the bloodstream
  • d) The colon absorbs nothing
Answer **b.** Note that (a) is false and matters — genuine toxicology exists, and real poisoning has real, specific medical treatments. The problem with the commercial claim is that its toxins are unnamed and therefore unmeasurable, and the organs described as needing rescue are working continuously.

11. The claim "95% of your serotonin is made in your gut, so gut health controls mood" fails primarily because:

  • a) The 95% figure is fabricated
  • b) Serotonin does not meaningfully cross the blood–brain barrier, so gut and brain serotonin are effectively separate pools
  • c) The gut produces no serotonin
  • d) Mood is unaffected by physiology
Answer **b.** The statistic is broadly accurate and irrelevant to the conclusion. Note the verdict was 🟡 rather than ❌ — the gut–brain axis is real and there are plausible routes (vagal signalling, immune mediators, microbial metabolites, tryptophan availability). What's unsupported is the specific therapeutic certainty.

12. Which of the following would you expect after removal of a large section of the ileum?

  • a) Inability to digest starch
  • b) B12 deficiency and fat-soluble vitamin malabsorption
  • c) Loss of stomach acid production
  • d) Complete inability to absorb protein
Answer **b.** B12 absorption is ileum-specific, and bile salts are reabsorbed there and recycled — lose that and the bile salt pool depletes, fat absorption suffers, and the vitamins carried with fat (A, D, E, K) go with it.

True / False

One-line justification.

13. Food in your stomach is inside your body.

Answer **False.** Topologically the gut lumen is continuous with the outside world. Nothing is *in* you until it crosses the gut wall into blood or lymph — which is why eating and absorbing are different events.

14. Combining protein and starch in one meal impairs digestion.

Answer **False.** Pancreatic amylase and pancreatic proteases operate simultaneously in the same bicarbonate-neutralized small intestine. Every whole food is already a mixture. Food-combining trials show no advantage over calorie-matched controls.

15. Fiber contributes zero calories.

Answer **False**, though close. You can't digest it, but your colonic bacteria ferment it into short-chain fatty acids which you *do* absorb — roughly 2 kcal/g, arriving by a different route and having fed your gut lining on the way.

16. Increased intestinal permeability is a fabricated concept with no basis in physiology.

Answer **False.** Permeability is real, measurable, and genuinely increased in celiac disease, IBD, some infections, and heavy alcohol use. What's unsupported is "leaky gut syndrome" as a marketed cause of chronic illness treated by a supplement stack — and whether permeability is cause or consequence remains open, with evidence mostly favouring consequence.

17. You should eliminate gluten first and get tested for celiac disease afterward if symptoms improve.

Answer **False, and this one matters.** Celiac serology requires gluten in the diet to be valid. Eliminating first can make the diagnosis impossible without a supervised gluten challenge. **Test before you eliminate** — this is the chapter's single most consequential clinical line.

Short Answer

18. Explain in three or four sentences why a large fatty meal keeps you full longer than an isocaloric meal of juice and white bread. Name at least two mechanisms.

Answer **Gastric emptying:** fat arriving in the duodenum triggers hormonal brakes that slow the stomach's release rate substantially, so it stays distended longer; liquids and refined starch clear quickly. **Hormonal signalling:** fat and protein trigger CCK, and nutrients reaching the ileum trigger GLP-1 and PYY, all of which promote fullness — whereas rapidly absorbed sugar produces a much weaker satiety signal. **Fiber** (absent from juice and white bread) would slow emptying further and provide fermentation substrate.

19. A friend feels genuinely better after a ten-day juice cleanse. Without dismissing their experience, explain what most likely changed.

Answer Their experience is real data — about how they feel, not about toxin removal. During those ten days they almost certainly also: stopped drinking alcohol, stopped eating ultra-processed food, increased vegetable and fruit intake, slept more (people who commit to a cleanse usually commit to a whole regime), reduced caffeine, and paid deliberate attention to their body for the first time in months. Any of those alone could account for feeling better. **The intervention worked; the mechanism claimed for it did not** — and every genuinely useful component is available for free and indefinitely, without the $150–$400.

20. Why does the location of the brush-border enzymes explain both lactose intolerance and the malabsorption seen in untreated celiac disease?

Answer Brush-border enzymes are anchored to the microvilli on the surface of intestinal cells — digestion finishes at the doorstep, and absorption happens immediately. **Lactose intolerance** is the loss of *one* enzyme (lactase) at that site: one sugar goes undigested. **Celiac disease** is autoimmune destruction of the villi themselves — you lose the surface, and with it many enzymes and much absorptive area at once. That's why lactose intolerance produces one specific problem and untreated celiac disease produces multiple simultaneous deficiencies. You haven't lost an enzyme; you've lost carpet.

Applied Scenario

21. A 34-year-old comes to you having lost 40 lb after gastric bypass surgery eighteen months ago. They report that their appetite changed "within about four days" of the operation, long before meaningful weight loss. They've recently stopped taking their prescribed supplements because they "feel fine."

Explain (a) the appetite change and (b) what you would be most concerned about, and why.

Answer **(a) The appetite change.** Four days is far too fast for weight loss to explain anything. Bypass procedures rearrange the gut in ways that change hormone secretion: ghrelin (hunger) falls, and nutrients reaching the distal intestine sooner increase GLP-1 and PYY (fullness). Much of the effect is **hormonal rather than mechanical restriction** — which is why bypass outperforms what its calorie arithmetic predicts, and why the appetite change precedes the weight change. **(b) The concern: micronutrient deficiency, and it is serious.** Bypass alters or excludes the parts of the tube where specific nutrients are absorbed. The high-risk list includes **vitamin B12** (intrinsic factor and ileal absorption both potentially compromised), **iron** (duodenal absorption often bypassed, and reduced acid impairs it further), **calcium and vitamin D**, **fat-soluble vitamins A, E, and K** if fat absorption is impaired, **thiamine** — which can cause serious neurological damage and can appear surprisingly quickly, particularly with vomiting or poor intake — and **folate**. "Feeling fine" is exactly what you'd expect early: several of these deficiencies are asymptomatic for months to years and then cause damage that may be irreversible, particularly the neurological ones. ⚠️ **This person needs to resume supplementation and get laboratory monitoring, through their bariatric team, promptly.** Post-bariatric micronutrient supplementation is lifelong and not optional, and this is a scenario where reading a textbook is not a substitute for a clinician.

Scoring

Score Reading
18–21 Strong. The anatomy is in place; move on.
14–17 Good. Reread §3.4 (small intestine) and §3.7 (hormones).
10–13 Reread §3.4 carefully — it carries most of the chapter's load — then redo Exercise C1.
Under 10 Reread the chapter. Chapters 11, 22, 27, 28, and 29 all lean on this material.