Nutrition Macronutrients Vitamins Minerals And Supplements

---
name: nutrition-macronutrients-vitamins-minerals-and-supplements
description: "Use for the nutrient layer: protein and amino acids including quality and requirements, carbohydrates, fibre and glycaemic response, fats and lipids and what the saturated fat evidence actually shows, alcohol, the vitamins and the minerals with deficiency and toxicity ranges, and supplements sorted by what the evidence supports. Technical orientation, not medical or dietary advice."
---

# Nutrition Science: Protein and Amino Acids, Carbohydrates and Fibre, Fats and Lipids, Alcohol, Vitamins, Minerals, and Supplements

> **Part 2 of 6** of the *Food and Nutrition Science* reference (plugin `food-and-nutrition-science`), covering §4–§10. Sibling skills: `nutrition-epistemics-study-design-and-measurement` (§0–§3), `nutrition-digestion-energy-balance-appetite-and-food-processing` (§11–§18), `nutrition-dietary-patterns-weight-regulation-and-life-stages` (§19–§23), `nutrition-live-evidence-and-reading-a-claim` (§24–§25), `nutrition-reference` (§26–§30). Section numbers are shared across the set; a reference written as §N → `skill` points into that sibling skill.
>
> **Currency:** The biochemistry is settled; the applied layer is contested. Two areas are live. See §24 → `nutrition-live-evidence-and-reading-a-claim` for ultra-processed foods, and the 2025-2030 US Dietary Guidelines.

> **⚠️ A field where the biochemistry is solid, the epidemiology is weak, and the public
> discourse is almost entirely disconnected from both.** ⚠️ **The gap between what
> nutrition science can actually establish and the confidence of nutrition headlines is
> wider than in almost any other discipline** — **and understanding WHY (§1–§3 → `nutrition-epistemics-study-design-and-measurement`) matters
> more than memorizing any particular finding.**
>
> **Complements a cooking/cleaning reference (food safety and the chemistry of cooking),
> an exercise physiology reference (§12's energy expenditure), and a psychology reference
> (§1 → `nutrition-epistemics-study-design-and-measurement`'s replication context).**
>
> **⚠️ GOTCHA** boxes mark the claims that outrun their evidence.
>
> **⚠️ Two things stated up front.** ⚠️ **First, this is a reference on the SCIENCE — it is
> not personalized advice, and individual circumstances (medication, pregnancy, kidney or
> liver disease, absorption disorders) change the answers substantially.** ⚠️ **Second,
> §22 → `nutrition-dietary-patterns-weight-regulation-and-life-stages` covers disordered eating and is placed BEFORE the diet content deliberately,
> because nutrition information is not neutral for everyone who reads it.**
>
> **The three ideas that organize this document:**
> 1. **⚠️ Almost all nutrition epidemiology is confounded, and the confounding runs the
>    same direction every time** (§2 → `nutrition-epistemics-study-design-and-measurement`). **Healthy-user bias means the people who follow any
>    dietary advice differ systematically from those who don't.**
> 2. **⚠️ Dietary PATTERNS are better supported than single nutrients** (§19 → `nutrition-dietary-patterns-weight-regulation-and-life-stages`). **Decades of
>    single-nutrient reductionism produced reversals; the whole-diet literature has held
>    up better.**
> 3. **⚠️ The measurement instrument is the field's foundational weakness** (§3 → `nutrition-epistemics-study-design-and-measurement`). **Most
>    large studies rest on people remembering what they ate, and that error is not random.**

---

## §4. Protein and Amino Acids

**⚠️ Nine essential amino acids; ⚠️ protein QUALITY reflects amino acid profile and
digestibility (DIAAS has largely superseded PDCAAS).**
**⚠️ Functions**: **structural, enzymatic, transport, immune, and ⚠️ a minor energy
substrate — protein is not primarily fuel.**
**⚠️ The "complete protein" myth**: ⚠️ **you do not need complementary proteins at the same
meal.** **The body maintains an amino acid pool; combining across the day is sufficient,
and this correction is decades old but still repeated wrongly.**
**⚠️ Reference intakes** (⚠️ **the RDA of ~0.8 g/kg/day is a population-level minimum to
prevent deficiency, NOT an optimum**) — ⚠️ **and the research literature on older adults
and on resistance training generally supports higher intakes than the RDA** (see an
exercise physiology reference).
**⚠️ Protein and kidneys**: ⚠️ **higher protein intake is not established as harmful to
healthy kidneys; it does matter in existing kidney disease, which is where the concern
originated.**
**⚠️ Plant vs animal**: ⚠️ **plant proteins are generally lower in leucine and less
digestible, which is addressable by quantity and variety.**

---

## §5. Carbohydrates and Fibre

```
SIMPLE  monosaccharides (glucose, fructose, galactose), disaccharides
COMPLEX  starch (amylose, amylopectin), ⚠️ RESISTANT STARCH (behaves
   like fibre; ⚠️ cooking and COOLING starchy foods increases it)
⚠️ FIBRE  soluble (viscous — cholesterol and glycaemic effects) vs
   insoluble (bulk and transit). ⚠️ FERMENTABLE fibre feeds the
   microbiome and produces short-chain fatty acids (§14)
⚠️ GLYCAEMIC INDEX  ⚠️ a property measured in isolation, on a fixed
   carbohydrate dose, with wide between-person variability.
   ⚠️ GI of a single food poorly predicts the response to a MEAL,
   which is why GI-based advice has underperformed
```
**⚠️ Fructose**: ⚠️ **metabolized largely in the liver; the concern is dose and context.**
**⚠️ Fruit is not the problem — the fibre, water and volume make overconsumption difficult;
sugar-sweetened beverages deliver the same sugar with no satiety** (§13 → `nutrition-digestion-energy-balance-appetite-and-food-processing`).
**⚠️ Fibre is one of the better-supported nutrients** — ⚠️ **and intake is well below
recommended levels in most Western populations.**

---

## §6. Fats and Lipids

```
SATURATED (SFA) · MONOUNSATURATED (MUFA) · POLYUNSATURATED (PUFA)
⚠️ TRANS  ⚠️ industrial trans fats are the clearest dietary harm ever
   established, and their near-elimination is a real public health win
⚠️ OMEGA-3  ALA (plant) → EPA/DHA conversion is POOR in humans;
   marine sources supply EPA/DHA directly
OMEGA-6  ⚠️ linoleic acid. ⚠️ The "omega-6 causes inflammation" claim
   is much weaker than commonly stated — trials generally do not
   show the predicted inflammatory effect
⚠️ CHOLESTEROL  ⚠️ DIETARY cholesterol has modest effects on SERUM
   cholesterol for most people. ⚠️ This was the basis for removing
   the specific dietary cholesterol limit from guidelines
LIPOPROTEINS  ⚠️ LDL-C, HDL-C, ⚠️ ApoB and Lp(a) as better markers
```
> **⚠️ GOTCHA — saturated fat is the genuinely contested case, and both camps overstate.**
> ⚠️ **The evidence that saturated fat raises LDL-C is strong.** **⚠️ The evidence on hard
> outcomes depends entirely on the REPLACEMENT (§1 → `nutrition-epistemics-study-design-and-measurement`): replacing SFA with PUFA appears
> beneficial; with refined carbohydrate, not.** **⚠️ Meta-analyses disagree, partly by which
> substitutions they model.**
> **⚠️ Meanwhile "saturated fat was never a problem" overstates the revisionist case,
> which is why §24.2 → `nutrition-live-evidence-and-reading-a-claim`'s guidelines retained the 10% limit while simultaneously promoting
> foods high in it — a contradiction critics have flagged.**

---

## §7. Alcohol

**⚠️ Ethanol provides ~7 kcal/g; metabolized via alcohol dehydrogenase to acetaldehyde
(⚠️ a carcinogen and the cause of the flushing response in people with ALDH2 variants).**
**⚠️ The J-curve is the important reversal**: ⚠️ **older observational studies suggested
moderate drinkers had lower mortality than abstainers.** **⚠️ Subsequent analyses found
the abstainer group contaminated by "sick quitters" — people who stopped drinking because
of illness — and Mendelian randomization studies generally do not support a protective
effect.** ⚠️ **The current scientific direction is that there is no clearly established
level of alcohol that improves health, and cancer risk rises from low levels.**
**⚠️ Note §24.2 → `nutrition-live-evidence-and-reading-a-claim`'s guidelines weakened the specific numeric limits, which is contested.**

---

## §8. Vitamins

**⚠️ Fat-soluble (A, D, E, K — stored, and ⚠️ toxicity is possible) vs water-soluble
(B complex, C — excess largely excreted, with exceptions like B6 neuropathy at high
doses).**
**⚠️ Notable specifics:**
- ⚠️ **Vitamin D is the most-studied and most-disappointing supplement of recent decades:
  strong observational associations, and large RCTs (VITAL and others) largely failing to
  show benefit for the outcomes predicted.** ⚠️ **Low vitamin D may be substantially a
  MARKER of poor health rather than a cause.** **Deficiency is real and treatable; the
  supplement-everyone hypothesis did not hold.**
- ⚠️ **B12 is genuinely required from animal sources or supplements** — **a real concern
  for vegans, and deficiency causes irreversible neurological damage.**
- ⚠️ **Folate fortification is one of public health nutrition's clearest successes**, **and
  ⚠️ folic acid can mask B12 deficiency, which is why the interaction matters.**
- ⚠️ **Vitamin A toxicity from retinol is real; beta-carotene is not equivalent.**

---

## §9. Minerals

**⚠️ Macrominerals (calcium, phosphorus, magnesium, sodium, potassium, chloride) and trace
(iron, zinc, iodine, selenium, copper, manganese, chromium, molybdenum, fluoride).**
```
⚠️ IRON  heme (animal, well absorbed) vs non-heme (plant, poorly
   absorbed; ⚠️ vitamin C enhances, phytates and tannins inhibit).
   ⚠️ Deficiency is the most common nutrient deficiency globally;
   ⚠️ excess is harmful and iron is not a supplement to take casually
⚠️ SODIUM/POTASSIUM  ⚠️ the RATIO matters, and most populations are
   high sodium and low potassium. ⚠️ Sodium reduction lowers blood
   pressure; the magnitude of mortality benefit is contested
⚠️ CALCIUM  ⚠️ supplementation shows weaker fracture benefit than long
   assumed, with some cardiovascular signals debated
⚠️ IODINE  ⚠️ deficiency remains the leading preventable cause of
   intellectual disability worldwide; salt iodization is a triumph
⚠️ ZINC and SELENIUM  narrow windows between deficiency and toxicity
```

---

## §10. ⚠️ Supplements

> **⚠️ The general finding across decades: supplements correct DEFICIENCIES well and
> produce disappointing results in replete populations.**
```
⚠️ GOOD EVIDENCE  folate in pregnancy · B12 where intake is absent ·
   vitamin D where deficient · iron where deficient · iodine ·
   ⚠️ specific clinical situations (bariatric surgery, malabsorption)
⚠️ MIXED / WEAK  omega-3 for cardiovascular prevention · multivitamins
   in well-nourished people · most single antioxidants
⚠️ EVIDENCE OF HARM  ⚠️ beta-carotene in smokers · high-dose vitamin E ·
   ⚠️ antioxidants around training may blunt adaptation
```
**⚠️ The regulatory reality in the US and many jurisdictions**: ⚠️ **supplements are not
approved for safety or efficacy before sale, and independent testing repeatedly finds
products that do not contain the stated amount, or that contain undeclared
pharmaceuticals.** **⚠️ Third-party certification is the practical mitigation.**
**⚠️ Interactions are real** — ⚠️ **St John's wort induces drug metabolism, vitamin K
interacts with warfarin, and high-dose supplements can interfere with medication.**

---

# PART III — PHYSIOLOGY