Chapter 8 — Quiz

Twenty-one questions. Attempt before opening.

Multiple Choice

1. The RDA for protein in adults is 0.8 g/kg. This figure represents:

  • a) The optimal intake for health
  • b) The minimum adequate intake for 97–98% of healthy individuals
  • c) The maximum safe intake
  • d) The average intake in the population
Answer **b.** It's a **floor** — the amount below which deficiency becomes likely. Like the vitamin C RDA preventing scurvy: useful, and not a claim that scurvy-avoidance is your health goal.

2. Nitrogen balance studies are thought to underestimate protein requirements because:

  • a) They were done only in athletes
  • b) Losses through sweat, skin, and hair are hard to collect and systematically underestimated
  • c) They measured the wrong nitrogen
  • d) They used too large a sample
Answer **b.** Plus two other limitations: balance isn't the same as optimal (you can be in balance while slowly losing muscle), and short studies allow adaptation to low intakes to look like adequacy.

3. IAAO-based estimates of adult protein requirements generally fall around:

  • a) 0.5 g/kg
  • b) 0.8 g/kg — confirming the RDA
  • c) 1.0–1.2 g/kg
  • d) 2.5 g/kg
Answer **c.** Notably higher than the nitrogen-balance figure, which is the main reason the chapter treats 0.8 as a floor with a known downward bias.

4. Protein intake during an energy deficit should be:

  • a) Lower, to reduce metabolic load
  • b) The same as at maintenance
  • c) Higher — 1.6–2.4 g/kg
  • d) Irrelevant
Answer **c.** Higher, not lower — because lean tissue is at risk when energy is short, and because gluconeogenesis is pulling on amino acids (Ch 6 §6.7). This determines whether you end up lighter and stronger or lighter and weaker.

5. "Complete protein" means the source:

  • a) Contains all twenty amino acids
  • b) Contains all nine essential amino acids in proportions meeting human needs
  • c) Is from an animal
  • d) Is fully digestible
Answer **b.** Soy, quinoa, and buckwheat are generally considered complete among plant sources. Most grains are limiting in **lysine**; most legumes in **methionine**.

6. DIAAS is considered superior to PDCAAS mainly because it:

  • a) Is simpler to calculate
  • b) Uses ileal rather than faecal digestibility and is not capped at 1.0
  • c) Only applies to plant proteins
  • d) Ignores amino acid profile
Answer **b.** The PDCAAS cap hides real differences above 1.0, and faecal digestibility overestimates true absorption. DIAAS **widens** the measured animal–plant gap, which is an honest point plant-forward advocates sometimes skip.

7. Leucine matters particularly because it:

  • a) Is the most abundant amino acid in muscle
  • b) Is the primary dietary trigger for mTOR and muscle protein synthesis
  • c) Cannot be obtained from plants
  • d) Is used for gluconeogenesis
Answer **b.** Protein supplies both building material *and* a signal, and the signal has a threshold — roughly 2.5–3 g of leucine per dose in young adults, more in older ones.

8. The protein-combining rule was:

  • a) Never actually claimed by anyone
  • b) Popularized by Frances Moore Lappé in 1971 and retracted by her in the 1981 edition
  • c) Confirmed by later research
  • d) Invented by the meat industry
Answer **b.** The amino acid pool does the combining across the day. A retraction that took forty years to propagate is a case study in its own right.

9. The muscle protein synthesis response to a single protein dose plateaus at roughly:

  • a) 5–10 g in everyone
  • b) 20–40 g in young adults, higher in older adults
  • c) 100 g regardless of age
  • d) There is no plateau
Answer **b.** Roughly 0.24–0.40 g/kg per feeding in young adults. It shifts higher with age, with larger training volumes, and with lower-quality protein.

10. The "anabolic window" after resistance training is best described as:

  • a) 30 minutes
  • b) 2 hours
  • c) Many hours, plausibly 24 or more, with total daily intake dominating
  • d) Nonexistent — timing never matters
Answer **c.** Early studies were confounded by whether participants trained fasted. Someone who trains fasted does benefit from eating soon after — because they haven't eaten, not because a window is closing.

11. Anabolic resistance means that older adults:

  • a) Cannot build muscle at all
  • b) Need a larger protein dose to produce the same muscle protein synthesis response
  • c) Absorb less protein
  • d) Should reduce protein to protect their kidneys
Answer **b.** The threshold rises — studies suggest closer to 35–40 g per meal with adequate leucine. Which is why **requirements go up with age** exactly as appetite, chewing, taste, and cooking all push intake down.

12. High protein intake in people with healthy kidneys:

  • a) Causes progressive kidney damage
  • b) Increases glomerular filtration rate as normal functional adaptation, without demonstrated harm
  • c) Has never been studied
  • d) Is prohibited by all guidelines
Answer **b.** ⚠️ **The exception is real:** in existing chronic kidney disease, protein restriction is genuine evidence-based management set by a nephrologist and renal dietitian. Two different claims, routinely conflated.

13. The acid-ash hypothesis about protein and bone was overturned primarily because:

  • a) Protein doesn't produce acid
  • b) The increased urinary calcium is substantially explained by increased intestinal absorption, and outcome evidence associates higher protein with better bone density
  • c) Bones don't contain calcium
  • d) Nobody tested it
Answer **b.** The observation was real, the interpretation wrong. And the reversal matters practically: the older adults told to limit protein for their bones were exactly the people who most needed more for their muscles.

14. Which is the cheapest source of 20 g of protein?

  • a) Protein bar
  • b) Greek yogurt
  • c) Dried lentils
  • d) Chicken breast
Answer **c.** Roughly $0.25 versus $2.50–$3.50 for a bar — about a tenfold difference for the same protein. Note that protein *powder* sits mid-table and is a reasonable convenience tool; the expensive nonsense is the snackified end.

True / False

One-line justification.

15. Vegetarians must eat rice and beans at the same meal to get complete protein.

Answer **False.** The circulating amino acid pool, continuously replenished by intake *and* by 200–300 g/day of turnover, makes meal-by-meal combining unnecessary. **The honest residual:** plant proteins are less digestible and lower in leucine, so plant-based eaters should aim 10–20% higher on total protein.

16. Older adults should eat less protein than young adults because they're less active.

Answer **False, and this is the chapter's central inversion.** Anabolic resistance means they need **more** — 1.0–1.2 g/kg, up to 1.5 with illness — precisely because their bodies use it less efficiently. Ruth's "I'm not doing anything, why would I need it?" is exactly backwards.

17. You can only absorb about 30 g of protein per meal.

Answer **False.** That's the *muscle protein synthesis* plateau, not an absorption limit. You absorb essentially all of it; the surplus goes to enzymes, immune proteins, gut lining turnover, connective tissue, or is oxidized.

18. Protein supplements are necessary to reach a 1.6 g/kg target.

Answer **False**, though convenient. Trials show supplemental protein works and isn't superior to equivalent food protein. Most people can reach 1.2 g/kg from food without effort and many can reach 1.6. **Fix breakfast before you buy a tub.**

19. Protein plus resistance training is more effective for sarcopenia than either alone.

Answer **True.** Each without the other substantially underperforms. This is why Ruth's plan included a community strength class twice a week alongside the food — and why food-only advice for an older adult losing function is doing half the job.

Short Answer

20. Ruth is 79, weighs 58 kg, and eats 42 g of protein daily across tea-and-toast, a cheese sandwich, and "something small." Calculate her g/kg, her target, and the gap. Then explain why her distribution is a separate problem from her total.

Answer **42 ÷ 58 = 0.72 g/kg** — below the RDA of 0.8, against a target of **1.0–1.2 g/kg = 58–70 g.** Gap: roughly **16–28 g/day.** **The distribution problem is separate and arguably worse.** Her three meals contain roughly 5 g, 15 g, and 20 g. At seventy-nine, with anabolic resistance, her per-meal threshold is *higher* than a young adult's — closer to 35–40 g with adequate leucine. **Not one of her meals crosses it.** So even if she hit her daily total by adding a snack, she could still be failing to stimulate muscle protein synthesis meaningfully at any point in the day. Which is why her plan targeted **breakfast specifically** — milk in the porridge and a boiled egg — rather than just "eat more protein."

21. Explain why higher protein is well supported for muscle and function while the longevity evidence is contested — and how someone should act under that uncertainty.

Answer **Well supported:** lean mass retention in a deficit, satiety, thermic effect, bone density, and — most strongly — muscle and functional outcomes in older adults, where the evidence is convergent (Ch 2 §2.10) and the clinical stakes are independence. **Contested:** some animal and observational work associates lower protein — and lower mTOR signalling (Ch 6 §6.9) — with longer lifespan. The human data is inconsistent and complicated by protein source, by age, and by what protein *displaces* in the diet. **Acting under the uncertainty:** notice that the two bodies of evidence apply most strongly to different life stages. It is entirely possible the optimum is **lower in midlife and higher in later life**, and the current evidence cannot settle it. Given that the downside of under-eating protein at 75 is losing the ability to get out of a chair, and the downside of eating adequate protein at 45 is speculative and derived largely from mice, **the asymmetry of consequences favours meeting the functional targets** — while staying genuinely open to revision. Anyone who tells you they know the longevity-optimal protein intake is extrapolating from model organisms.

Scoring

Score Reading
18–21 Strong. You can now advise on protein better than most fitness content.
14–17 Good. Reread §8.3 (the table) and §8.10 (older adults).
10–13 Reread §8.2 and §8.6 — the floor-not-target idea and the dose/window distinction.
Under 10 Reread the chapter. Chapters 23, 24, and 25 all build on it.

And do Exercise C6 — ask an older relative what they ate yesterday. It's the most consequential five minutes in this chapter.