Chapter 27 — Exercises

Three tiers. 🔄 retrieval; 🪞 reflection.

Tier 1 — Recall and Comprehension

R1. ⚠️ What was the old bacteria-to-human-cell ratio, what is it now, and what does the correction illustrate?

R2. Give six functions of the gut microbiota. ⚠️ Which is the main event?

R3. Compare 16S rRNA sequencing with shotgun metagenomics on four dimensions.

R4. ⚠️ Name the four things NEITHER sequencing method tells you.

R5. ⚠️ Give §27.3b's seven sources of divergence between two labs analysing the same stool. Is any of it fraud?

R6. State the four reasons consumer microbiome testing receives ❌.

R7. Name the three main SCFAs. ⚠️ Which feeds colonocytes, and what does that mean?

R8. ⚠️ Which six chapters converge on fermentable fibre, and why does the chapter call that its strongest structural argument?

R9. ⚠️ Give §27.4b's ranking of what changes the microbiome. What's first and what's last?

R10. ⚠️ Why does §27.4b say some people are "measuring their prescription"?

R11. What are human milk oligosaccharides, and why does the chapter say they're such direct evidence?

R12. Give three reasons diversity is a poor individual target.

R13. ⚠️ State the strain-specificity principle. Why does it matter commercially?

R14. ⚠️ List the indications where probiotic evidence is reasonable, with verdicts. What happened with paediatric gastroenteritis?

R15. ⚠️ Describe the three findings in §27.7 that changed how the field thinks. Which is counterintuitive?

R16. ⚠️ Describe the fermented food trial: design, comparison, and both findings. Give the three qualifications.

R17. ⚠️ Which fermented foods contain live microbes and which don't? What's the difference between "pickled" and "fermented"?

R18. ⚠️ Why does FMT work so well for recurrent C. difficile and poorly elsewhere?

R19. ⚠️ Give the three phases of low-FODMAP and name the failure mode. What does staying in phase 1 cost?

R20. ⚠️ What is exclusive enteral nutrition, and what is it established for?

Tier 2 — Application

A1. 🔄 Read the report. Theo's PDF gave a score of 64/100, said Akkermansia was low, and advised reducing oats, apples and onions.

a) ⚠️ What is wrong with the score specifically? b) What would you need to know before acting on the Akkermansia finding? c) ⚠️ What is the actual harm in the food recommendations? d) Write the four-sentence reply you'd give him.

A2. Grade the product. For each, say whether there is evidence and what you'd need to know:

a) A supermarket yoghurt drink "with billions of friendly bacteria" b) Saccharomyces boulardii for someone starting a week of antibiotics c) A £45/month "gut restore" powder with glutamine, collagen and slippery elm d) L. reuteri DSM 17938 for a breastfed six-week-old with colic e) A probiotic recommended after a course of antibiotics to "restore your gut"

A3. ⚠️ The IBS pathway. Someone has had IBS symptoms for two years and wants to try low-FODMAP.

a) What should come first? b) ⚠️ What must you tell them about the structure before they start? c) What is the single question you'd ask at their six-week review? d) ⚠️ What non-dietary options should they know about?

A4. The antibiotics question. Someone is prescribed a week of antibiotics.

a) ⚠️ What does §27.4b say about the magnitude of this event? b) Is there a probiotic worth taking, and for what? c) ⚠️ What does §27.7 say about "restoring your gut afterwards"? d) What would you actually advise, in three sentences?

A5. Sort the fermented foods. Which contain live microbes as eaten?

sourdough bread · kefir · red wine · unpasteurized kimchi · shop pickles in vinegar · miso soup made with boiling water · tempeh · pasteurized sauerkraut · live yoghurt · kombucha

⚠️ Two are trick items. Which, and why?

A6. ⚠️ The leaky gut conversation. Someone tells you they've been diagnosed with leaky gut and is on a protocol.

a) What's real in the underlying concept? b) ⚠️ What isn't? c) Write the reply using Chapter 17 §17.13's rules — concede the true part first.

Tier 3 — Analysis and Synthesis

S1. ⚠️ Established versus interesting. The chapter's organizing distinction.

a) Sort every finding in this chapter into the two categories. b) ⚠️ What features distinguish them? Write a test. c) Apply your test to three claims from other chapters. Does it work?

S2. The convergence argument. §27.4 claims six chapters converging on fibre is the book's strongest structural argument.

a) ⚠️ Is convergence from six directions actually stronger than one good trial? When? b) Construct a case where six fields converge and are all wrong for the same reason. c) ⚠️ Does that failure mode apply to fibre?

S3. ⚠️ The post-antibiotic finding. Probiotics delayed recovery relative to spontaneous recovery and autologous FMT.

a) Propose two mechanisms. b) ⚠️ The chapter holds it at moderate confidence. Justify that — why not higher, why not lower? c) ⚠️ If it replicates, what should change in clinical practice, and who would resist?

S4. Fermented food versus fibre. The trial's fibre arm did not increase diversity in ten weeks.

a) ⚠️ Give three interpretations, and say which you favour. b) Design the study that would distinguish them. c) ⚠️ How should a textbook handle a result that appears to contradict a much larger body of evidence measured on different outcomes? Assess how this chapter did.

S5. ⚠️ The commercial gap. §27.14's closing box notes that after a chapter on the most commercially active area in nutrition, the actionable output is beans, yoghurt, reintroduction and fewer antibiotics.

a) Why is this area so commercially active relative to its yield? Give three structural reasons. b) ⚠️ Chapter 21 §21.14b said "who profits?" is necessary and not sufficient. Apply it here. c) ⚠️ What would have to happen for the yield to catch up? Is that likely?

S6. 🔄 The two honest positions. §27.13.

a) ⚠️ Which column do you actually sit in? b) Write the strongest objection to your own position. c) ⚠️ Both columns give identical practical advice. This is the seventh time in the book. What conclusion should a reader draw about public argument by now?

🪞 Reflection

M1. ⚠️ Have you bought, or considered buying, a microbiome test? What did you want it to tell you? Would any answer have changed what you eat?

M2. ⚠️ Do you take a probiotic? Can you name the strain? Can you name the indication?

M3. §27.4b puts probiotics last and antibiotics first. ⚠️ Does that reordering change anything for you?

M4. ⚠️ If you or someone you know is on a restricted diet for gut symptoms — how long, and was there ever a reintroduction plan?

M5. 🔄 ⚠️ Theo paid £179 to be told to eat fewer oats, apples and onions. What's the most you've spent on health information that turned out to point the wrong way? What made it convincing?