Are seed oils bad for you? What the heart studies show

Seed oils in place of butter and lard lower LDL cholesterol and, in long-term trials, heart attacks. Pooled studies find no harm and no rise in inflammation.

Published October 2026

Short answer

The scare isn't supported: seed oils don't raise heart risk, and replacing saturated fat with them lowers LDL cholesterol and, in long-term trials, heart attacks and strokes. Benefits are clearest for people at higher heart risk. Evidence grade B (Moderate). Pooled analyses of 8-19 randomised trials plus large cohort analyses of linoleic acid; downgraded for inconsistency between reviews (the omega-6-specific trials show little event benefit) and risk of bias in the older trials.

Key takeaways

Replacing saturated fat with polyunsaturated fat cut heart attacks and heart-disease deaths by 19% across 8 long-term trials of 13,614 people [1].
Swapping saturated fat for polyunsaturated fat lowered LDL cholesterol by about 10 mg/dL in 24 controlled feeding trials [2].
Trials that raised omega-6 fat intake found no rise in deaths or heart events and possibly fewer heart attacks; the review rated that evidence low-quality [3].
The inflammation claim did not hold up: two reviews of randomised trials found no rise in CRP, IL-6 or other inflammatory markers [4].
Two re-analyses of 1960s-70s trials found no mortality benefit and possible harm from diets built on linoleic-acid-rich oils [5][6].

The short version

Seed oils — canola, soybean, sunflower, corn, safflower and similar cooking oils high in omega-6 fat — have been blamed for heart disease on social media [7]. The human evidence doesn't support that worry: when these oils replace saturated fat such as butter or lard, LDL ('bad') cholesterol falls and long-term trials show fewer heart attacks and strokes [2][8][1]. Large studies also link higher linoleic acid, the main fat in seed oils, to lower heart disease and death [9].

What the studies show

LDL cholesterol. In controlled feeding trials, swapping saturated fat for polyunsaturated fat lowers LDL cholesterol [2]. A 2025 meta-analysis of 24 trials with 1,011 adults found diets higher in polyunsaturated fat lowered LDL by about 10 mg/dL on average, and by about 16 mg/dL when the diets really differed in saturated fat [2]. A 2026 meta-analysis of 53 trials (1,690 people) found high-polyunsaturated diets also beat high-monounsaturated ('olive-oil-style') diets for LDL — by about 3 mg/dL [10].

Heart attacks and strokes. Long-term trials that replaced saturated fat with unsaturated oils found fewer heart problems. A 2020 Cochrane review of 15 randomised trials with about 59,000 people found reducing saturated fat cut combined cardiovascular events by 21% (risk ratio 0.79) over two years or more; the trials that lowered cholesterol the most saw the biggest drop [8]. An earlier meta-analysis of 8 trials (13,614 people) found replacing saturated fat with polyunsaturated fat reduced heart attacks and heart-disease deaths by 19% (RR 0.81) [1]. A 2026 review of 17 trials (66,337 people) found the reduction in non-fatal heart attacks was clearest when saturated fat was replaced by polyunsaturated fat (RR 0.75), with meaningful benefits mainly in people at higher heart risk [11].

Raising omega-6 specifically. Cochrane's review of 19 trials that increased omega-6 fats (6,461 people, one to eight years) found no increase in deaths (RR 1.00) or cardiovascular events (RR 0.97), a possible reduction in heart attacks (RR 0.88) and a small fall in total cholesterol (0.33 mmol/L) [3].

Large studies. Pooled data from 30 studies with 68,659 people found higher blood or tissue linoleic acid was linked to lower risk of cardiovascular disease (HR 0.93), cardiovascular death (HR 0.78) and stroke (HR 0.88) [9]. An analysis of 38 studies (811,069 people) found higher linoleic acid intake or levels went with about 13% lower all-cause mortality and roughly 11-13% lower cardiovascular and cancer mortality [12]. In the 135,335-person PURE study, higher polyunsaturated fat intake was linked to 20% lower total mortality (HR 0.80) [13]. These studies are observational: they can show links, not cause and effect.

Inflammation. The claim that seed oils cause inflammation doesn't hold up in trials. A meta-analysis of 30 trials (1,377 people) found no significant change in C-reactive protein, IL-6, TNF or other inflammatory markers when linoleic acid intake increased; a rise in CRP was suggested only in people whose intake rose the most [4]. An earlier review of 15 trials found the same [14]. A 2026 review of the whole controversy concluded that claims about inflammation, oxidative stress and harmful processing by-products lack scientific support [7].

Where the doubt comes from. Two re-analyses of old trials are the main counterweight. In the Sydney Diet Heart Study, 458 men who had recently had a heart attack had higher death rates when their saturated fat was replaced with safflower oil: 17.6% died versus 11.8% of controls [5]. Recovered data from the Minnesota Coronary Experiment (9,423 people) found cholesterol fell on the corn-oil diet but deaths did not [6]. A meta-analysis that split trials by the type of polyunsaturated fat found omega-6-only diets did not reduce heart attacks or heart deaths (RR 1.13) [15]. Cochrane's own conclusion was more cautious than the pooled numbers suggest: it found no evidence that raising omega-6 intake reduces cardiovascular outcomes other than heart attacks [3].

The nuances

Benefits aren't the same for everyone. The 2026 review found little meaningful benefit within five years for people at low heart risk, and clearer reductions in heart attacks for people at higher risk [11]. The same body of trials couldn't show that replacing saturated fat with polyunsaturated fat worked better than replacing it with carbohydrate-rich foods [8] — the benefit comes from what seed oils replace [1].

Beyond the heart, an umbrella review of 150 cohort papers found higher omega-6 intake linked to lower overall cancer risk but higher risks of ovarian and endometrial cancers — a mixed picture from observational data that can't show cause [16].

Safety: trials that raised omega-6 fats for up to eight years reported no increase in serious adverse events [3]. People with severe soy or peanut allergy should ask a doctor about specific oils, because traces of protein can survive refining in some products [17]. Repeated high-heat frying of polyunsaturated oils forms oxidation products; most concern comes from lab and animal studies, and human trials are still lacking [18]. The seed oils topic page has the full safety details.

What this means for you

If you are choosing what to spread, drizzle or cook with, the trials put seed oils ahead of butter and lard for cholesterol and heart risk when they take the place of those saturated fats [2][8]. If your heart risk is high — you already have heart disease or several risk factors — that trade looks more worthwhile than for someone at low risk [11]. In the trials, the benefit came from seed oils replacing saturated fat, and the higher-polyunsaturated diets didn't increase deaths or heart attacks [1][3].

Go deeper

Seed Oils — Seed oils such as canola, soybean, sunflower and corn are high in omega-6 linoleic acid.