Replacing lard and butter with vegetable oils for cooking: you don’t need to switch oils for health reasons, nor should you expect flaxseed oil to protect your heart

Cost: It doesn’t cost much extra. Vegetable oils are already the main choice in most households; the real challenge is breaking the habit of using lard or butter for stir‑frying and seasoning.
In plain terms: Cutting back on saturated fats like lard and butter and switching to vegetable oils lowers the risk of heart disease and stroke by roughly 17%. However, overall mortality shows no change. There is no evidence that swapping between soybean oil, corn oil, or canola oil makes any difference. Even consuming large amounts of flaxseed oil does not appear to reduce heart disease risk.
Benefit: A Cochrane review analyzed 15 randomized trials involving 56,675 participants, each followed for at least two years. Reducing saturated fat intake lowered the combined incidence of cardiovascular events by about 17% (RR 0.83, 0.70–0.98). Total mortality remained virtually unchanged (RR 0.96, 0.90–1.03) as did cardiovascular death (RR 0.95, 0.80–1.12). No significant difference was found between replacing saturated fats with polyunsaturated fats (the main component of soybean and corn oils) or with carbohydrates. Data on replacing them with monounsaturated fats (dominant in canola and olive oils) are too limited to draw conclusions. Another Cochrane review of 19 trials with 6,461 participants found that higher intake of omega‑6 fatty acids (linoleic acid) had no effect on overall mortality (RR 1.00, 0.88–1.12) or cardiovascular events (RR 0.97, 0.81–1.15). A third review of 86 trials involving 162,796 participants showed that increased consumption of plant‑derived omega‑3 fatty acids (found in flaxseed oil and perilla oil) had virtually no impact on overall mortality (RR 1.01, 0.84–1.20) or coronary events (RR 1.00, 0.82–1.22).
Evidence grade: A
Sources:Hooper L, Martin N, Jimoh OF, 等 (2020). Reduction in saturated fat for cardiovascular disease. Cochrane Database of Systematic Reviews, (5), CD011737. https://doi.org/10.1002/14651858.CD011737.pub3；Hooper L, Al-Khudairy L, Abdelhamid AS, 等 (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；Abdelhamid AS, Brown TJ, Brainard JS, 等 (2020). Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews, (3), CD003177. https://doi.org/10.1002/14651858.CD003177.pub5；中国营养学会 (2022). 中国居民膳食指南（2022）. 人民卫生出版社
Notes: Controversy: Some argue that the high omega‑6 content in soybean and corn oils promotes inflammation, so they recommend limiting or replacing these oils. The aforementioned omega‑6 study found no harmful effects, though the authors rated the evidence quality as low. The magnitude of benefit—a 17% reduction in cardiovascular events—is considered moderate, while overall mortality shows no change. Regardless of the oil type, portion control is essential; dietary guidelines suggest a daily limit of 25–30 grams of cooking oil per person.