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Food Β· Β§347
Seed Oils
Fifty years ago your kitchen fat came from animals or olives. Now most is pressed from seeds β€” soybean, sunflower, canola β€” 10% of the calories Americans eat. You've heard they're poison, or heart-healthy, depending on who yelled last. The honest read: the real damage is in deep-fried restaurant food, home cooking with olive oil and butter is a safe default, and most of the rest is genuine uncertainty. Fix the one exposure that isn't uncertain and you're most of the way there.
Avoid Β· Daily Evidence Mixed Chapter Food

What's actually settled

Seed oils reliably drop LDL-C by 10–15% versus animal fat 1, and swapping them in cuts heart attacks and strokes by about 17% 2. That's the mainstream case, and it holds.

The catch: the same review finds no effect on how long people live 2. Cholesterol dropped, events fell, lifespan didn't move. Two 1960s trials whose full data surfaced only decades later found the linoleic-acid group did slightly worse 3. Nobody has run the trial that would settle it.

The fryer isn't contested. Heat linoleic acid to frying temperature and it breaks into toxic aldehydes the food soaks up β€” measured directly in fast-food fries 4. Reused restaurant oil is the worst of it.

What to do

Extra-virgin olive oil runs 5–10Γ— the cost of soybean β€” about $50–200 a year for a household. Butter and ghee are cheap. The real cost is eating out less.

What you get

The closest thing to a settled win is a Mediterranean trial that's really a seed-oil-swap in disguise: 7,447 high-risk adults, and the extra-olive-oil group had about 30% fewer heart attacks, strokes, and cardiovascular deaths over five years than the low-fat control 6.

It comes as a package: swap the oil, eat more fish, cook at home, eat less fried food. You can't isolate which piece did it, and you don't need to.

The fine print β€” when to skip it, and what people get wrong

"Smoke point is the safety number." No β€” aldehydes form well below it, hours before any visible smoke 4. "All seed oils are the same." Canola has only 20% linoleic acid; safflower has 70%+. Canola sits closer to olive oil than to soybean. "Essential, so more is better." Your body needs about 1–2% of calories as linoleic acid; the average American eats 7–8% 7. Iron is essential too, and you can still overdose on it.

If you only do one thing, make it the deep-fryer, not the pantry β€” the bottle on your counter is the weakest exposure, the restaurant fryer the strongest. Swapping your home oil while still eating fries twice a week is the common way to feel virtuous and change little.

References
  1. 1Mensink RP (2016). Effects of saturated fatty acids on serum lipids and lipoproteins: a systematic review and regression analysis. link
  2. 2Hooper L, Martin N, Jimoh OF, Kirk C, Foster E, Abdelhamid AS (2020). Reduction in saturated fat intake for cardiovascular disease. Cochrane Database of Systematic Reviews. link
  3. 3Ramsden CE, Zamora D, Majchrzak-Hong S, Faurot KR, Broste SK, Frantz RP, Davis JM, Ringel A, Suchindran CM, Hibbeln JR (2016). Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73). BMJ. link
  4. 4Grootveld M, Percival BC, Leenders J, Wilson PB (2020). Potential adverse public health effects afforded by the ingestion of dietary lipid oxidation product toxins: significance of fried food sources. Nutrients. link
  5. 5Simopoulos AP (2016). An increase in the omega-6/omega-3 fatty acid ratio increases the risk for obesity. Nutrients. link
  6. 6Estruch R, Ros E, Salas-SalvadΓ³ J, et al. (2018). Primary Prevention of Cardiovascular Disease with a Mediterranean Diet Supplemented with Extra-Virgin Olive Oil or Nuts. New England Journal of Medicine. link
  7. 7Blasbalg TL, Hibbeln JR, Ramsden CE, Majchrzak SF, Rawlings RR (2011). Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century. American Journal of Clinical Nutrition. link
Related in the handbook (5)
Related
  • β€” The seed-oil fight is ultimately about heart risk β€” ApoB is the number that measures it more directly than the debate does.
  • β€” The omega-3 debate is partly about balancing the omega-6-heavy seed oils most people already eat a lot of.
  • β€” Cooking vegetables with fat boosts their nutrients β€” but which oil you use is its own contested debate.
  • β€” An adjacent topic in the handbook.
  • β€” Seed oils are a marker ingredient of ultra-processed food, but the processing β€” not the oil alone β€” is the bigger issue.
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