Chapter 11 — Quiz

Nineteen questions. Attempt before opening.

Multiple Choice

1. Dietary fiber is defined as:

  • a) Carbohydrate from plants
  • b) Carbohydrate that human enzymes cannot digest
  • c) Insoluble plant matter
  • d) Anything that causes bowel movements
Answer **b.** A definition by *absence*, which is why the category is chemically heterogeneous — cellulose, pectin, beta-glucan, inulin, gums, resistant starch, and lignin have almost nothing in common except that your small intestine can't break them down.

2. The chapter argues you should replace "soluble vs. insoluble" with four properties. They are:

  • a) Sweet, bitter, sour, salty
  • b) Viscosity, fermentability, bulk/water-holding, particle size
  • c) Plant, animal, mineral, synthetic
  • d) Cheap, expensive, common, rare
Answer **b.** Soluble/insoluble isn't wrong, it's just not the property that predicts what a fiber *does* — the same failure mode as simple/complex in Chapter 7.

3. Which property is responsible for LDL lowering?

  • a) Bulk
  • b) Fermentability
  • c) Viscosity
  • d) Particle size
Answer **c.** Viscous fiber gels and traps bile acids, preventing ileal reabsorption. The liver makes more bile acids from cholesterol, pulling LDL from circulation. **A non-gelling fiber traps nothing** — which is why wheat bran is excellent for constipation and does little for cholesterol.

4. Butyrate is:

  • a) A type of fiber
  • b) A short-chain fatty acid produced by colonic fermentation, and the preferred fuel of colon cells
  • c) A bile acid
  • d) A supplement ingredient with no evidence
Answer **b.** Your gut lining is partly fed by bacteria, from material you couldn't digest. This is the mechanistic core of why fiber matters.

5. The 2019 Lancet review found the greatest reductions in outcomes at fiber intakes around:

  • a) 10–14 g/day
  • b) 15–19 g/day
  • c) 25–29 g/day
  • d) 50–60 g/day
Answer **c.** With a clear dose-response relationship, and curves suggesting **benefit continuing above that range.**

6. The Adequate Intake for fiber is best expressed as:

  • a) 20 g/day for everyone
  • b) 14 g per 1,000 kcal consumed
  • c) 5% of energy
  • d) One serving of vegetables per meal
Answer **b.** Which works out to about 38 g/day for adult men and 25 g/day for adult women under 50, and scales sensibly with how much you eat.

7. Approximately what proportion of adults meet the fiber recommendation?

  • a) About 50%
  • b) About 25%
  • c) About 5%
  • d) About 80%
Answer **c.** Roughly one in twenty. **There is no other nutrient where the gap between what we know and what people do is this wide.**

8. One cup of cooked lentils contains approximately:

  • a) 3 g fiber
  • b) 8 g fiber
  • c) 15 g fiber
  • d) 30 g fiber
Answer **c.** Nearly two-thirds of a woman's daily target, in one cheap shelf-stable ingredient. **Nothing else comes close per serving or per dollar** — which is why "beans, mostly" is the honest answer.

9. How much fiber is in meat, fish, eggs, dairy, and oils?

  • a) A small amount
  • b) About half that of vegetables
  • c) Zero
  • d) It varies by preparation
Answer **c.** Which is not an argument against eating them — it's the explanation for why a diet composed largely of animal foods contains no fiber at all, and why that's the specific thing to worry about with it.

10. The recommended rate of increase when raising fiber intake is approximately:

  • a) As fast as possible
  • b) 5 g per week
  • c) 5 g per month
  • d) 20 g per week
Answer **b.** With increased fluid alongside, spread across meals, starting with better-tolerated sources, and expecting 2–4 weeks of adjustment. **The way most people fail at fiber is by succeeding at it too fast.**

11. Psyllium is unusually well tolerated because it is:

  • a) Highly fermentable
  • b) Viscous and water-holding but only modestly fermentable
  • c) Completely inert
  • d) Absorbed in the small intestine
Answer **b.** Which is why it can normalize stool in **both** constipation and diarrhea, and why it's often the right choice in IBS where highly fermentable fibers worsen symptoms.

12. The chapter's verdict on fiber supplements is 🟡 because:

  • a) They don't work at all
  • b) Psyllium has good evidence for specific intermediate outcomes, but the hard-outcome evidence comes from fiber-rich diets, not supplements
  • c) They are dangerous
  • d) They are too expensive
Answer **b.** This is the whole-food fallacy from the beta-carotene case: *observed in food → inferred to a compound → tested as a pill.* A supplement delivers isolated fiber and displaces nothing.

13. Fiber scores "zero for seven" on which list?

  • a) Health benefits
  • b) The requirements for being commercially marketable
  • c) Safety concerns
  • d) Digestibility measures
Answer **b.** Not patentable, low margin, not novel, not counterintuitive, offers no identity, has no enemy, produces no fast visible results. **Which is why you've heard so little about the best-evidenced intervention available to almost everyone.**

True / False

One-line justification.

14. Fiber has no calories.

Answer **False**, though close. Colonic fermentation returns roughly **2 kcal/g** as short-chain fatty acids — arriving by a different route, hours later, having fed your gut lining on the way.

15. Bloating when increasing fiber means fiber is irritating your gut.

Answer **False.** Gas is the byproduct of fermentation — the process that produces butyrate. Transient discomfort during a rapid increase is an adaptation problem with a known solution (ramp at 5 g/week). **Feeling less bloated is not the same as being healthier.**

16. Adding bulk-forming fiber always helps constipation.

Answer **False, and this is a common clinical own-goal.** Adding bulk without adequate fluid can *worsen* constipation. And in slow-transit constipation, more bran without assessment can make things worse. Fluid is not optional.

17. People with IBS should reduce total fiber intake.

Answer **False, usually.** The answer is generally **different fiber, not less fiber** — viscous, less-fermentable options like psyllium are often well tolerated while highly fermentable ones (inulin, large legume servings, wheat fructans) drive symptoms. A supervised, **temporary** low-FODMAP approach with structured reintroduction may help identify triggers.

18. The fiber evidence includes long-term randomized trials with hard endpoints.

Answer **False**, and the chapter says so explicitly. It meets nearly every other convergence criterion — dose-response, consistency across populations, multiple designs, seven independent mechanisms — but the definitive trial doesn't exist and won't. **Healthy-user bias still applies, and it doesn't stop applying because the conclusion is convenient.**

Short Answer

19. Explain the bile acid mechanism in four sentences, and say why it means viscosity specifically matters.

Answer The liver makes bile acids from cholesterol and secretes them into the duodenum to emulsify fat; they are then reabsorbed at the ileum and recycled, with most being recovered. **Viscous fiber forms a gel that traps some bile acids**, preventing their reabsorption so they leave in the stool. The liver, to maintain its bile acid pool, must make more — and it makes them from cholesterol, so it **increases cholesterol uptake from the bloodstream** and blood LDL falls. **Viscosity is the operative property** because a non-gelling fiber traps nothing. It's also structurally the same mechanism as the bile acid sequestrant drug class — psyllium is a gentler version of a pharmaceutical, for about twenty cents.

Applied Scenario

20. Camila Ortiz eats roughly 10 g of fiber a day. She works three twelve-hour night shifts a week, eats her main meal at 3 a.m. from a vending machine or break room, cooks nothing on shift days, has $180/week for a household of four, and a four-year-old who eats nine foods.

Get her to 25 g. Then say what you would not do.

Answer **The constraint that dominates: three days a week she has no kitchen.** Any plan built around cooking fails 43% of the time, and a plan that fails 43% of the time is not a plan. **Shift days — a portable box, assembled on a non-shift day (~4 minutes, ~$1.80):** - Tinned chickpeas or beans, drained, dressed — 1 cup, **12 g** - Wholemeal bread or oatcakes — **4 g** - An apple or pear — **4–6 g** - A handful of almonds — **3.5 g** → **≈ 23–25 g**, no fridge needed for a shift, and it replaces a vending machine. **Non-shift days — two additive changes to food the family already eats:** - Porridge instead of toast at her breakfast — **+6 g** - A tin of beans into whatever Erik is already cooking — **+6–8 g per serving**, additive so nobody has to be persuaded and Alma can ignore it (Chapter 7's Case Study 1 principle). **Total ≈ 25–28 g both kinds of day, under $4/week for the household.** **What I would NOT do:** - Tell her to meal-prep on Sundays — she's sleeping. - Recommend fresh vegetables that die during an overrun shift (Dominic's failure, Chapter 10 Case Study 1). - Address her fiber before acknowledging that **she is eating from a vending machine at 3 a.m., which is a logistics problem wearing a nutrition costume.** - Suggest a fiber supplement as the first move — it would work, and it costs more than the beans and fixes none of the meal. **And I'd ramp it**, not switch overnight: 10 g → 15 → 20 → 25 across four weeks, with fluid.

Scoring

Score Reading
17–20 Strong. Now go do the ramp — knowing this changes nothing on its own.
13–16 Good. Reread §11.2 (the four properties) and §11.8 (the ramp).
9–12 Reread §11.4–§11.6. The evidence and the gap are the chapter's argument.
Under 9 Reread the chapter — but do the Project Checkpoint regardless. It's the highest-yield thing in Part II.