The claim: Avoid seed oils to lower inflammation
Are seed oils inflammatory? What the trials show
Against, as stated. Evidence grade: Probable.
Published Updated
The book tests this claim twice, in a table and in the chapter that owns the subject. Both verdicts are below, each with its own evidence and sources.
Chapter 2's table of nine claims: "Avoid seed oils to lower inflammation"
Against, as stated
The evidence
A systematic review of randomized trials found that linoleic acid, the omega-6 fat plentiful in seed oils, had no significant effect on blood markers of inflammation in healthy adults. It does not speak to existing metabolic disease (Chapter 5).18
The "What you've heard" box in Chapter 5: "Seed oils such as soybean, corn and canola are inflammatory poisons behind modern disease"
Unsupported as stated
Unsupported as stated. Evolutionary novelty is not evidence of harm.
The evidence
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
Settle the dairy question with a two-week trial, not a DNA kit
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.How: if milk reliably brings bloating, gas or cramps, switch to lactose-free dairy, or take a lactase enzyme with dairy, for two weeks. Then drink ordinary milk again on purpose and see what happens. Fermented dairy such as yogurt is often fine when milk is not. Why: losing lactase after childhood is the normal state for most adults on earth. Persistent gut symptoms still deserve a doctor, since celiac disease and inflammatory bowel disease can imitate lactose trouble.
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.
Related claims
- Is the carnivore diet supported by evidence?Self-reported only, no trials.Evidence grade: Emerging. Early, small, animal-only, or actively contested.
- Do detox teas and juice cleanses work?Unsupported.
- Should people without diabetes wear a glucose monitor?No evidence of benefit for people without diabetes.Evidence grade: Emerging. Early, small, animal-only, or actively contested.
- Is 8 glasses of water a day a myth?False as a rule.Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
Sources
Chapter 2's table of nine claims
- 18.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. https://doi.org/10.1016/j.jand.2012.03.029 (15 randomized controlled trials)
Note numbers are those of Chapter 2, What Your Body Expects, and How to Trust This Book.
The "What you've heard" box in Chapter 5
- 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 nine in the table Chapter 2 uses to show how the book judges a claim: find the primary study, and grade the claim by what it measured. The grade rates the evidence behind the verdict, by the book's stated method.
Educational content, not medical advice. Disclaimer.