"Seed oils are toxic and are the main cause of chronic inflammation" — Checked.

• moderateRepeatedly heated and reused frying oil forms reactive aldehydes; the chemistry is established and cell/animal data suggest harm. Human health effects at real-world exposures are much less well quantified, and this is an argument about fryer practice, not a sealed bottle
• moderateIndustrial refining generates process contaminants — glycidyl esters and 3-MCPD esters. EFSA's expert panel treated glycidol as genotoxic and carcinogenic and flagged glycidyl esters as a health concern; the highest reported levels were in palm oil and fat, which is usually absent from the anti-seed-oil villain list
• moderatePopulation exposure genuinely changed: linoleic acid content of US adipose tissue rose substantially across the second half of the twentieth century. A changed exposure is a reason to study something, not evidence of harm
• moderateTwo recovered historical trials (Sydney Diet Heart; Minnesota Coronary Experiment) found no mortality benefit from replacing saturated fat with vegetable oil, and signals of higher mortality in some analyses. These are serious papers — with the caveats that the intervention fats of the era contained trans fat and that one population was institutionalised with short average exposure
• moderateIn a randomised trial in adults with frequent migraine, a diet that raised omega-3 while lowering omega-6 reduced monthly headache days compared with control — narrow population, specific endpoint, and the omega-3 increase may be doing much of the work
• strongNutrition science carries documented funding problems, including industry-funded reviews from the 1960s that shaped how dietary fat and sugar were weighted — grounds for humility about mid-century consensus, not proof the resulting advice was wrong

• contradictedThat dietary linoleic acid raises systemic inflammation — pooled randomised trials in healthy adults found essentially no change in CRP, IL-6, TNF-α or fibrinogen over weeks-to-months exposures
• contradictedThe mechanism itself: that eating more omega-6 meaningfully raises tissue arachidonic acid and pro-inflammatory eicosanoids. Direct human data indicate conversion is rate-limited at Western intakes
• noneThat seed oils are the main cause of chronic inflammation at a population level — no study has isolated them as a dominant driver against adiposity, smoking, inactivity, sleep and infection
• weakThat "seed oils" form a single toxicological category — fatty-acid profiles differ widely between and within crops (canola is comparatively low in linoleic acid; high-linoleic safflower is mostly linoleic acid), and olive and avocado oils are frequently refined by similar industrial processes
• noneThat residual hexane at regulated trace levels in refined oils harms humans — there is no human evidence of harm at those exposures, and limited direct study of them
• contradictedThat swapping to saturated animal fats improves cardiovascular outcomes — pooled trial evidence points the other way for cardiovascular events (with no clear effect on all-cause mortality), and biomarker-based cohorts associate higher circulating linoleic acid with lower cardiovascular and total mortality
• noneThat removing seed oils is the active ingredient when people feel better after cutting them — in Western diets seed oil intake travels with ultra-processed food, which has its own randomised evidence of driving substantially higher calorie intake. No trial has isolated seed-oil removal from the rest of the dietary change

1. meta Johnson GH, 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. Funding and affiliation disclosures in this corner of the literature are contested; the design — pooled RCTs with objective markers — is the appropriate test regardless. Limited to healthy adults and weeks-to-months exposures.
2. meta Rett BS, Whelan J (2011). Increasing dietary linoleic acid does not increase tissue arachidonic acid content in adults consuming Western-type diets: a systematic review. Nutrition & Metabolism. Directly tests the mechanism the claim rests on. Does not resolve whether genetic high-converter subgroups behave differently.
3. meta Hooper L, Martin N, Jimoh OF, et al. (2020). Reduction in saturated fat intake for cardiovascular disease. Cochrane Database of Systematic Reviews. Cochrane review; benefit concentrated where saturated fat was replaced by polyunsaturated fat, and seen for cardiovascular events rather than all-cause mortality. Narrower than most headlines imply in either direction.
4. rct Ramsden CE, Zamora D, Majchrzak-Hong S, et al. (2016). Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from the Minnesota Coronary Experiment (1968-73). BMJ. The strongest trial-level counter-evidence, in a major journal. Institutionalised population, high turnover, short average exposure, era-typical intervention fats. That the data went unpublished for decades is a genuine failure of publication practice.
5. rct Ramsden CE, Zamora D, Leelarthaepin B, 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. Recovered-data reanalysis; the intervention margarine of the period contained trans fat, which is a live alternative explanation.
6. rct Ramsden CE, Zamora D, Faurot KR, et al. (2021). Dietary alteration of n-3 and n-6 fatty acids for headache reduction in adults with migraine: randomized controlled trial. BMJ. Single trial, migraine-specific endpoint. The arm that both raised omega-3 and lowered omega-6 performed best, so the omega-3 increase is not separable from the omega-6 reduction.
7. observational Marklund M, Wu JHY, Imamura F, et al. (2019). Biomarkers of dietary omega-6 fatty acids and incident cardiovascular disease and mortality: an individual-level pooled analysis of 30 cohort studies. Circulation. Pooled individual-level data across tens of thousands of participants, biomarker-based rather than food questionnaires. Removes recall error; cannot remove confounding by health-conscious behaviour.
8. observational Guyenet SJ, Carlson SE (2015). Increase in adipose tissue linoleic acid of US adults in the last half century. Advances in Nutrition. Documents the exposure change only. Says nothing about whether the change caused harm.
9. meta EFSA CONTAM Panel (2016). Risks for human health related to the presence of 3- and 2-monochloropropanediol (MCPD), and their fatty acid esters, and glycidyl fatty acid esters in food. EFSA Journal. Regulatory hazard assessment of refining contaminants — not a seed-oil verdict. Highest reported levels were in palm oil and fat; EU limits were subsequently tightened.
10. rct Hall KD, Ayuketah A, Brychta R, et al. (2019). Ultra-processed diets cause excess ad libitum energy intake and weight gain: an inpatient randomized controlled trial of ad libitum food intake. Cell Metabolism. Small inpatient randomised crossover with matched macronutrients; reported roughly 500 kcal/day higher intake on the ultra-processed arm. Does not isolate oils — which is exactly the confounding the seed-oil claim ignores.
11. observational Kearns CE, Schmidt LA, Glantz SA (2016). Sugar industry and coronary heart disease research: a historical analysis of internal industry documents. JAMA Internal Medicine. Historical document analysis, not a clinical study. Establishes that funding shaped mid-century review writing; does not by itself establish that any specific dietary conclusion was wrong.

No reader evidence was submitted for this claim.