What you've heard
Seed oils such as soybean, corn and canola are inflammatory poisons behind modern disease
Verdict
Unsupported as stated
Unsupported as stated. Evolutionary novelty is not evidence of harm.
Are seed oils inflammatory poisons?
Unsupported as stated. Evolutionary novelty is not evidence of harm.
Seed oils are a genuinely modern, high-volume food, and that novelty is the core of the case against them. When trials added linoleic acid, the main fat in these oils, to healthy people's diets, inflammatory markers did not rise. In cohorts across many countries, people with more linoleic acid in their blood had less heart disease and less diabetes, and in a large US cohort butter was linked to higher mortality and plant oils to lower. The other side deserves a fair hearing: data recovered from two trials run half a century ago found no benefit, and in one a hint of harm, when vegetable oil replaced saturated fat, and a major review found that more of this kind of fat may make little or no difference to deaths either way.23 Frying oil reused for hours, and the fried ultra-processed food it ends up in, are separate problems.
Where the book tests it
What the book recommends instead
Build meals on plants, legumes, and minimally processed protein and fats
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.How: fill half the plate with vegetables and fruit, a quarter with whole grains or potatoes, a quarter with protein, often beans, lentils or fish; cook with olive or another liquid plant oil; add a handful of nuts most days. Work up to at least 25 grams of fiber a day, slowly, to limit gas; in practice that means beans or lentils most days, whole grains in place of white bread and rice, and fruit or vegetables at every meal. Include a fermented food with live cultures most days, such as plain yogurt, kefir or kimchi (EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.; one small trial, see Chapter 6). Why: this is the pattern with trial support for heart events, and it lowered blood pressure within weeks (StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism. for blood pressure).
Drink to thirst
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.How: water with meals and when thirsty; coffee, tea, milk and water-rich food all count. Drink more in heat and hard exercise, and in long events never drink past thirst. Why: thirst is the one intake signal the modern world has left mostly intact.
Sources
- 23.Johnson, G.H., and Fritsche, K. (2012). "Effect of dietary linoleic acid on markers of inflammation in healthy persons: a systematic review of randomized controlled trials." Journal of the Academy of Nutrition and Dietetics, 112(7), 1029-1041.e15. https://doi.org/10.1016/j.jand.2012.03.029; Marklund, M., Wu, J.H.Y., Imamura, F., Del Gobbo, L.C., et al. (2019). "Biomarkers of dietary omega-6 fatty acids and incident cardiovascular disease and mortality." Circulation, 139(21), 2422-2436. https://doi.org/10.1161/CIRCULATIONAHA.118.038908; Wu, J.H.Y., Marklund, M., Imamura, F., Tintle, N., et al. (2017). "Omega-6 fatty acid biomarkers and incident type 2 diabetes: pooled analysis of individual-level data for 39 740 adults from 20 prospective cohort studies." Lancet Diabetes and Endocrinology, 5(12), 965-974. https://doi.org/10.1016/S2213-8587(17)30307-8; Zhang, Y., Chadaideh, K.S., Li, Y., Li, Y., et al. (2025). "Butter and plant-based oils intake and mortality." JAMA Internal Medicine, 185(5), 549-560. https://doi.org/10.1001/jamainternmed.2025.0205; Ramsden, C.E., Zamora, D., Leelarthaepin, B., Majchrzak-Hong, S.F., et al. (2013). "Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis." BMJ, 346, e8707. https://doi.org/10.1136/bmj.e8707; Hooper, L., Al-Khudairy, L., Abdelhamid, A.S., Rees, K., et al. (2018). "Omega-6 fats for the primary and secondary prevention of cardiovascular disease." Cochrane Database of Systematic Reviews, 11, CD011094. https://doi.org/10.1002/14651858.CD011094.pub4 (19 trials, 6,461 people; low to very low quality); Ramsden, C.E., Zamora, D., Majchrzak-Hong, S., Faurot, K.R., et al. (2016). "Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73)." BMJ, 353, i1246. https://doi.org/10.1136/bmj.i1246 (fifteen randomized trials in the inflammation review)
Note numbers are those of Chapter 5, Eat.
This verdict is one of the "What you've heard" boxes in Chapter 5, Eat, where the book tests the claims people repeat against the studies behind them.
Educational content, not medical advice. Disclaimer.