Chapter 21 — Self-Check Quiz

20 questions. Answers with explanations at the end. Aim for 16+.

Questions

1. A 16-hour fast places you:

• a) In a metabolically exotic state reached only by deliberate fasting
• b) In the post-absorptive band that anyone sleeping eight hours already enters nightly, extended by about four hours
• c) In deep ketosis
• d) Past the point of glycogen exhaustion

2. In 5:2, "fast days" typically involve:

• a) Complete abstention from food
• b) About 500–600 kcal
• c) Water only for 48 hours
• d) Unlimited eating in a 2-hour window

3. Ghrelin's pre-meal rise is:

• a) Purely a consequence of an empty stomach
• b) Anticipatory and entrained to habitual meal times, falling again if the expected meal doesn't come
• c) Unrelated to eating schedules
• d) Constant throughout the day

4. A hunger wave typically:

• a) Increases monotonically until you eat
• b) Passes in roughly 20–30 minutes whether or not you eat
• c) Lasts several hours
• d) Only occurs after 24 hours

5. When calories are matched, intermittent fasting versus continuous energy restriction produces:

• a) Substantially more weight loss
• b) Comparable weight loss, without clear superiority
• c) Substantially less weight loss
• d) No weight loss in either group

6. The 12-month NEJM trial (2022) is the cleanest test of Claim 3 for weight because it:

• a) Was the largest ever run
• b) Compared TRE plus calorie restriction against calorie restriction alone — both arms restricted, only one restricted the window
• c) Used continuous glucose monitoring
• d) Was double-blinded

7. Yoshinori Ohsumi's 2016 Nobel Prize was awarded for:

• a) Demonstrating that 16-hour fasts extend human lifespan
• b) Elucidating the mechanisms of autophagy, largely in yeast
• c) Developing the 5:2 protocol
• d) Discovering ghrelin

8. Rodent fasting durations don't map onto human clock time because:

• a) Rodents cannot fast
• b) A rodent's metabolic rate per unit mass is several times higher, making 24 hours a far larger perturbation
• c) Rodents lack autophagy
• d) Rodent studies use different clocks

9. The autophagy claim receives ⚗️ rather than 🟠 because:

• a) It has been tested and failed
• b) The human dose-response has not been established, and measuring autophagy in living humans is genuinely difficult
• c) Autophagy is not real
• d) The Nobel committee retracted it

10. Glucose tolerance across a normal day:

• a) Is constant
• b) Is generally better in the morning and declines across the day
• c) Is best at midnight
• d) Depends only on the previous meal

11. Sutton et al. (2018) is important because it:

• a) Was a large free-living trial
• b) Used early time-restricted feeding under eucaloric conditions and reported metabolic improvement without weight loss
• c) Compared 5:2 with alternate-day fasting
• d) Found no effects of any kind

12. §21.7's practical irony is that:

• a) Early windows are more popular than late ones
• b) The best mechanistic case is for early windows, and almost everyone practises late ones
• c) Nobody has studied timing
• d) Late windows have better trial support

13. During a fast of 24–72 hours, resting metabolic rate:

• a) Falls sharply into "starvation mode"
• b) Is maintained or slightly elevated, with norepinephrine rising
• c) Doubles
• d) Cannot be measured

14. The concern about lean mass in IF rests on the mechanism that:

• a) Fasting directly degrades muscle protein
• b) Compressing intake reduces the number of protein-driven muscle protein synthesis stimulation events, and total protein intake often falls
• c) Ketones dissolve muscle
• d) Fasting prevents resistance training

15. Which is §21.12's single most important contraindication entry?

• a) History of gallstones
• b) Any history of an eating disorder
• c) Shift work
• d) Vegetarianism

16. Older adults are flagged because:

• a) They cannot tolerate hunger
• b) Anabolic resistance plus fewer stimulation events plus lower total intake, against a background risk of sarcopenia and frailty
• c) Fasting is illegal for over-70s
• d) They have slower metabolisms

17. A key difference between Ramadan and most secular IF protocols is:

• a) Ramadan permits unlimited calories
• b) Ramadan restricts fluids as well as food
• c) Ramadan lasts a year
• d) There is no difference

18. "Does milk in my coffee break my fast?" is best answered by noting that:

• a) It definitively breaks the fast
• b) There is no biological event called breaking a fast — there is a continuous, dose-dependent response, and 10–20 kcal is trivial
• c) Only water is permitted
• d) It depends on the type of milk

19. On type 2 diabetes remission, the honest position is:

• a) Fasting uniquely causes remission
• b) Substantial weight loss can produce remission; fasting is a delivery mechanism, not the agent — and medication supervision is essential
• c) Remission is impossible
• d) Only surgery works

20. §21.14b argues that over-claiming about fasting occurs despite no commercial interest, driven principally by:

• a) Government guidelines
• b) Identity, a perceptible signal (hunger), effort-as-evidence, reliable early results, and a prestigious mechanism
• c) Pharmaceutical marketing
• d) Academic fraud

Answers

1. b) The normal overnight post-absorptive band, extended. ⚠️ Nothing switches (Chapter 6's threshold — mixing board, not gearbox). Much of the marketing describes 16 hours as crossing a physiological threshold; it doesn't cross one. Which isn't "it does nothing" — it means whatever it does is a matter of degree, and degree has to be measured. §21.3.

2. b) About 500–600 kcal. ⚠️ Which is not a fast. §21.4's "form" slot — the protocols are grouped under one word while differing in window, energy intake and timing. §21.1.

3. b) Anticipatory and entrained. ⚠️ It falls again after the expected meal time passes whether or not you eat, and the peaks follow when you shift the schedule. This is the honest explanation for Theo's "I'm not even hungry until eleven" — his ghrelin peaks moved, over days to a couple of weeks. §21.3.

4. b) Passes in 20–30 minutes. ⚠️ Which is why pushing through a peak is much easier than anticipating one — and why "it got easier after two weeks" is nearly universal. ⚠️ Note the symmetric implication: someone who habitually eats at 10pm feels genuine hunger at 10pm, and that's re-trainable too. §21.3.

5. b) Comparable, without clear superiority. ⚠️ "Comparable" is doing the work, and the public claim is almost always superiority. §21.5.

6. b) Both arms restricted calories; only one restricted the window. ⚠️ That isolates timing as the variable — the discriminating design, as in Chapters 18 and 19. §21.5.

7. b) The mechanisms of autophagy, largely in yeast. ⚠️ Not a fasting protocol. Citing a Nobel Prize for a claim it wasn't awarded for is a rhetorical move, not evidence — and autophagy is genuinely fundamental and beautifully characterized, which is what makes the move effective. §21.6.

8. b) Metabolic rate per unit mass. ⚠️ A 24-hour fast in a mouse is a far larger physiological perturbation than 24 hours in a person — by some estimates closer to several days. Rodent fasting durations do not translate to human clock time, and essentially every popular fasting-duration claim does that translation implicitly. §21.6.

9. b) The human dose-response is unestablished. ⚠️ This is the difference between ⚗️ and 🟠. Chapter 19's omega-6 chain was tested and the prediction failed (🟠). Autophagy's human dose has not been tested at all (⚗️). A failed test is more informative than no test — so ⚗️ is a different verdict, not a softer one. ⚠️ And "16 hours" is Chapter 17's sixth tell exactly: mechanism named, never dosed. §21.6.

10. b) Better in the morning, declining across the day. ⚠️ The same meal produces a larger glucose excursion in the evening than at breakfast, with insulin sensitivity following a daily rhythm and evening melatonin onset associated with impaired glucose handling. §21.7.

11. b) Eucaloric early TRE with metabolic improvement and no weight loss. ⚠️ A calorie-matched design showing timing effects — which is exactly what the weight trials weren't built to detect. Very small sample, controlled feeding rather than free-living: promising, not settled. §21.7.

12. b) Best case for early, almost everyone does late. ⚠️ 16:8 in practice usually means skip breakfast and eat until 8pm — close to the opposite of the version with better support. If timing matters, most people doing this for timing reasons are doing the version least likely to deliver it. §21.7.

13. b) Maintained or slightly elevated; norepinephrine rises. ⚠️ This directly contradicts "starvation mode" as popularly stated (Chapter 5 §5.6), and the fasting community was right about it before most of the diet world was. But "reset" still describes nothing — Chapter 17's dial-as-a- switch — and the elevation doesn't survive sustained deficit. §21.9.

14. b) Fewer stimulation events and lower total protein. Chapter 8 §8.6's anabolic resistance is the underlying physiology. ⚠️ The trial evidence is genuinely mixed — the TREAT lean-mass signal got as much methodological criticism as attention. The practical fix is unambiguous: hit your protein target inside the window and lift things. §21.8.

15. b) Any history of an eating disorder. ⚠️ And it doesn't require a diagnosis to count. §21.12's subsection gives four features that make IF unusually well-shaped to conceal disordered eating: a socially acceptable reason to refuse food · restriction reframed as compliance · a countable streak · and hunger reframed as the mechanism. Chapter 34.

16. b) Anabolic resistance + fewer events + lower intake. ⚠️ Three things compounding against a background risk of sarcopenia and frailty — and it is rarely flagged anywhere. §21.12.

17. b) Fluid restriction. ⚠️ Most secular protocols permit water; Ramadan does not, and in long summer days and hot climates dehydration is a genuine clinical consideration (Chapter 15). ⚠️ Also worth noting: Islamic jurisprudence contains established exemptions for illness, pregnancy, breastfeeding, menstruation, travel and age. A fourteen-century-old practice built in medical exemptions; the wellness protocols mostly haven't. §21.13.

18. b) No such biological event; it's a dose. ⚠️ A dose question wearing a purity costume — Chapter 20's binary, arriving again. And note the pattern: the item people most want policed is milk in coffee; the item that most obviously breaks the protocol is the 400 kcal butter coffee sold specifically to fasters. §21.14.

19. b) Weight loss is the agent; fasting is a delivery mechanism. ⚠️ Remission is real and changed clinical practice — but the trials that demonstrated it largely used total diet replacement, not intermittent fasting. ⚠️ And the safety point isn't optional: someone on insulin or a sulfonylurea who starts fasting without adjusting medication risks hypoglycaemia, and the risk rises as control improves. This is the one place in this book where "try it and see" is genuinely dangerous. §21.11.

20. b) Identity, sensation, effort, early results, prestigious mechanism. ⚠️ Fasting is free — Chapter 1 §1.5's "who profits?" finds nothing here, and the over-claiming happens anyway. Which means that question is necessary and not sufficient, and a reader who only asks it will be systematically blind to exactly this case. §21.14b.

Scoring

Three items worth checking regardless of score.

Question 9. ⚠️ If ⚗️ and 🟠 feel like the same verdict to you, reread §21.6. The distinction between tested and failed and not tested runs through the rest of the book.

Question 15. ⚠️ The section that matters most. If you skimmed it, go back.

Question 20. ⚠️ This is the chapter's structural finding, and it's the one that changes how you read everything else in Part IV.