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

It doesn’t cost much extra. Vegetable oils are already the main cooking oils in most households. The real challenge is breaking the habit of using lard or butter for stir-frying and flavoring meals.

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 rate of cardiovascular events by about 17% (RR 0.83, 0.70–0.98). Overall mortality remained virtually unchanged (RR 0.96, 0.90–1.03), as did cardiovascular-related deaths (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 (found in canola and olive oils) was too limited to draw conclusions. Another Cochrane review of 19 trials with 6,461 participants found that higher omega-6 intake (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 with 162,796 participants showed that increasing plant-based omega-3 intake (primarily from flaxseed and perilla oils) had virtually no impact on overall mortality (RR 1.01, 0.84–1.20) or coronary heart disease events (RR 1.00, 0.82–1.22).

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

Controversy: Some argue that high levels of omega-6 in soybean and corn oils promote inflammation, so these oils should be limited or replaced. However, the aforementioned studies on omega-6 showed no harmful effects, and the authors rated the evidence quality as low. The 17% reduction in cardiovascular events is considered a moderate benefit, while overall mortality shows no change. Regardless of the oil type, portion control is essential; dietary guidelines recommend 25–30 grams of cooking oil per person per day.