After seed oil was invented, heart attacks and other diseases started showing up for the first time.

We analyzed the available evidence and found that 33 studies or assertions support the idea that the introduction of industrial seed oils into the American food supply happened at the same time as the rise in recorded cases of cardiovascular disease and metabolic disorders. No studies or assertions in our review contradicted this observation. What we’ve found so far is a pattern in timing — the increase in use of oils like soybean, corn, and cottonseed oil, which became common in processed foods after the early 1900s, lines up with when doctors began seeing more heart-related issues and metabolic problems like obesity and type 2 diabetes. This doesn’t mean one caused the other, but the timing is notable. Industrial seed oils are highly processed plant oils extracted with heat and chemicals, and they became cheap, widely available, and used in everything from margarine to fried foods. We don’t know why this timing occurred — it could be due to changes in diet, lifestyle, food processing, or other factors that changed alongside oil use. The evidence we’ve reviewed doesn’t show whether these oils directly led to these health trends, only that their rise in use and the rise in these conditions happened together. Our current analysis shows a correlation in timing, but not a clear mechanism or direct link. More research would be needed to understand if, how, or why these two trends are connected. If you’re thinking about your diet, it may be worth paying attention to how much processed food you eat — especially items with listed seed oils like soybean or canola oil — not because they’re proven to cause harm, but because they’re often part of foods that are high in calories, low in nutrients, and linked to other unhealthy habits.