Chapter 11 — Exercises

C1 and C2 together are, for most readers, the highest-value forty minutes in this book. Everything else here is optional by comparison.

Difficulty legend: ⭐ basic recall · ⭐⭐ applied · ⭐⭐⭐ synthesis and judgment · ⭐⭐⭐⭐ extension

Selected answers in Appendix J.

Part A — Conceptual Understanding ⭐

A1. Define dietary fiber. Why is it "a definition by absence," and what follows from that?

A2. Why does the chapter say to drop soluble/insoluble? What replaces it?

A3. Name the four properties that matter, with a high example and a function for each.

A4. List the seven mechanisms by which fiber acts. Which one is "roughage," and where does it rank?

A5. Explain the bile acid mechanism for LDL lowering. Why does viscosity specifically matter?

A6. What did the 2019 Lancet review find? Name four outcomes and the intake range at which reductions were greatest.

A7. Which of Chapter 2 §2.10's criteria does the fiber evidence meet, and which does it not?

A8. State the fiber targets for adult men and women, and the per-1,000-kcal version. Roughly what proportion of adults meet them?

A9. How much fiber is in one cup of cooked lentils? How much is in 100 g of chicken?

A10. Give the six rules of the ramp protocol.

A11. What does psyllium do well, and what does the evidence not support supplements for?

A12. Name five situations where "eat more fiber" is the wrong advice.

A13. Why does the chapter say fiber scores "zero for seven" on the requirements for being marketed?

Part B — Applied Analysis ⭐⭐

B1. Match the fiber type to the purpose: lowering LDL · relieving constipation · feeding the microbiome · managing IBS symptoms. Give a specific food or supplement for each and say why.

B2. Theo eats 14 g against a 38 g target. Design his eight-week ramp with specific foods and weekly increments. Then estimate the weekly cost.

B3. A "high fiber" cereal contains 6 g per serving, mostly from added cellulose. A bowl of oats contains 4 g. Which is better for lowering LDL, and why?

B4. Someone increases fiber from 12 g to 35 g in three days, feels awful, and concludes fiber doesn't agree with them. Explain what happened, what they should have done, and why their conclusion is both understandable and wrong.

B5. Calculate: if lifetime colorectal cancer risk is 5% and higher fiber intake is associated with a 20% relative reduction, what is the absolute difference? Express it as cases per 100 people. Then say why the chapter argues this modest number is still a strong argument.

B6. Walt spends $187/month on supplements and eats 14 g of fiber against a 30 g target. Cost out closing his gap with (a) dried lentils, (b) tinned beans, (c) fiber gummies. Compare all three to his supplement spend.

B7. A patient with IBS says beans and onions cause severe symptoms and asks whether to go low-fiber. Answer properly, including what you'd suggest instead and what supervision is needed.

B8. Using §11.6's table, build a day reaching 38 g using only foods costing under $1 per serving.

Part C — Skills & Practice ⭐⭐–⭐⭐⭐

C1. Do the fiber audit. The Project Checkpoint: your number, your gap, your top three current sources, and how many legume servings you ate in three days.

C2. Build and start the ramp. Fill in the eight-week table with real foods you'd actually eat. Then start it. This is the exercise that matters.

C3. Make the legume commitment specific. Write the sentence: I will add __ to _ on ___. Not "eat more legumes." A food, a meal, and days of the week.

C4. Count servings for three days. The non-tracking version: count servings of legumes, whole grains, vegetables, fruit, nuts and seeds each day. Most people doing well land at 7–9. Where are you?

C5. Price the shelf. In a real shop, find cost per 10 g of fiber for: dried lentils, tinned beans, rolled oats, wholemeal bread, psyllium husk, a fiber supplement, and a "high fiber" snack bar. Rank them. Compare to §11.11's table.

C6. Read five fiber labels. Five packaged foods claiming fiber. Record grams per serving, whether the serving is realistic, the fiber source in the ingredient list (is it "chicory root fibre," "cellulose," or actual whole food?), and added sugars. Which claims survive?

C7. The one-week experiment. For one week, add one serving of legumes to one meal, three times. Record: cost, time added, whether anyone noticed, and how you felt. Then decide whether it's sustainable — which is the only question that matters (Chapter 10).

Part D — Synthesis & Critical Thinking ⭐⭐⭐

D1. The chapter says the fiber evidence is "about as good as nutrition gets" and that it's observational at its core, with healthy-user bias fully applicable. How confident should you actually be? Would you act on it? Justify the gap between your confidence and your action.

D2. Fiber supplements haven't reproduced the hard-outcome benefits seen with high-fiber diets. Give three explanations for this, and say which you find most likely. What would distinguish them?

D3. §11.11 argues that "the strength of the evidence for a nutrition intervention is roughly inversely proportional to how much you have heard about it." Test the claim: name three well-publicized interventions with strong evidence, and three obscure ones with weak evidence. Does the rule survive?

D4. The chapter opens with a room deflating at the word "fiber." If the boring answer cannot compete for attention, what should public health actually do? Is there an honest way to make fiber interesting, or is that inherently a form of the thing this book criticizes?

D5. Consider the ethics of the ⚠️ section. Fiber is genuinely wrong for some people, and books that recommend it enthusiastically rarely say so. How much space should a general recommendation devote to its exceptions? Who bears the cost if it doesn't?

Part M — Mixed & Interleaved Practice ⭐⭐–⭐⭐⭐

M1. (With Chapter 3.) Trace a cup of lentils from the mouth to the colon. What happens at each stage, what's absorbed where, and what reaches the colon? What does it produce there?

M2. (With Chapter 7.) The intact/refined axis and the fiber content of foods are closely related but not identical. Give an example of a refined food with meaningful added fiber, and say whether it behaves like an intact food. What does that tell you about the limits of the fiber number?

M3. (With Chapter 10.) Which diets in Chapter 10 are high in fiber and which are low? Using §11.4, say what that predicts — and note which prediction we cannot test.

M4. (With Chapter 9.) Both viscous fiber and replacing saturated fat with unsaturated fat lower LDL. Compare their mechanisms and their effect sizes. If someone could only do one, which and why?

M5. (With Chapter 4.) Explain how fiber helps with energy balance, naming at least three distinct mechanisms. Which of them requires no conscious effort at all?

M6. (With Chapters 2 and 5.) Walt takes berberine for glucose control. Compare the evidence base for berberine to the evidence base for fiber on the same outcome, using the evidence ladder. Then compare the costs.

M7. (With Chapter 8.) Legumes appear as the top recommendation in both Chapter 8 (cheapest protein) and Chapter 11 (highest fiber). Calculate what one cup of lentils delivers of both. Is there any other food this efficient?

M8. (Revisit at Chapter 27.) Predict now: how much of fiber's benefit will Chapter 27 attribute to the microbiome, and how confidently? Seal it.

Part E — Research & Extension ⭐⭐⭐⭐

E1. Read the Reynolds, Mann et al. 2019 Lancet systematic review and meta-analysis in full, including the dose-response figures. Note how the authors handle healthy-user bias and what they say about the trial versus observational components.

E2. Investigate the FDA-authorized health claims for oat beta-glucan and psyllium and blood cholesterol. What evidence was required? What are the exact permitted wordings, and why are they so carefully hedged? This is a good look at what "authorized health claim" actually means (Chapter 30).

E3. Look into bile acid sequestrant drugs (colestyramine, colesevelam). Compare their mechanism to viscous fiber's, and their effect size. Then consider what it means that a cheap food component and a prescription drug class share a mechanism.

E4. Research the low-FODMAP diet — its evidence base, its intended duration, and the concern that it is widely used as a permanent diet rather than a temporary diagnostic protocol. What are the risks of long-term FODMAP restriction? (Chapter 28 covers this; forming your own view first is better.)

E5. Investigate why fiber supplement trials haven't reproduced the outcome benefits of high-fiber diets. Find studies on isolated versus intrinsic fiber. Is this a food-matrix effect, a displacement effect, confounding in the observational data, or something else?

E6. Look at national fiber intake data over the last fifty years in any country with good survey data. Has it moved? What happened during the low-fat era and the low-carb era? Write a page connecting the trend to Chapters 7, 9 and 10.