Ask a Nutritionist: What are seed oils, and are they bad for my health?

Are seed oils as dangerous as people online are saying that they are?

Recently, seed oils have become a hot topic. Some people are concerned that these oils cause ramped inflammation, that the fats in them are unhealthy, and that we would all be better off consuming only animal fats. But how valid are these claims? Let’s explore where these misconceptions come from and look at the facts.

What are seed oils?

Seed oils are the oils extracted from seeds such as sunflower seeds, canola (rapeseed), and safflower. These oils are widely used in processed foods, restaurant cooking, and home kitchens due to their versatility and affordability.

Why are seed oils demonised? 

Seed oils often have a bad reputation because they are associated with fast foods and processed meals that lack nutritional value. As a result, many people link seed oils to the negative health impacts of junk foods. However, this association is more about the poor quality of diets and the reuse of frying oils in fast food settings than it is about the oils themselves.

For example, one study found that US adults are consuming more than twice as much omega-6 fatty acids in the last 50 years, largely due to seed oil consumption. This increase is more closely tied to the rise of fast foods in our diets than the seed oils themselves. It’s important to remember that correlation does not equal causation. Instead, maintaining a healthy balance of omega-6 to omega-3 fatty acids (a 4:1 ratio or lower) has been shown to be desirable for health.

Are omega-6 fatty acids in seed oils harmful? 

Contrary to popular belief, strong research involving human trials shows that omega-6 fatty acids, such as linoleic acid, are not inherently harmful. Omega-6 is an essential fatty acid, meaning it must be obtained through diet since the body cannot produce it.

Critics argue that omega-6 can convert into arachidonic acid, a precursor to both pro-inflammatory and anti-inflammatory molecules. However, the body only converts a minimal amount of omega-6 into arachidonic acid, and this process is tightly regulated.  A review of several randomized controlled trials—considered the gold standard in clinical research—found that linoleic acid does not increase inflammatory markers.

Why focus on human studies? 

While animal studies can provide insights into biological mechanisms, they don’t always translate directly to human outcomes. For example, mice are often given doses of substances far higher than typical human consumption levels, making human clinical trials a more reliable source when evaluating dietary impacts.

Can seed oils be part of a healthy diet? 

Yes, absolutely. A significant body of evidence shows that replacing saturated fats from sources like butter and lard with plant-based oils, including seed oils, can lower LDL cholesterol (the “bad” cholesterol). Canola oil, for example, is rich in monounsaturated fats and has a favourable omega-6 to omega-3 ratio of 2:1.

TL;DR?

Seed oils can be a healthy part of a balanced diet, and according to research, omega-6 fatty acids are not known to cause inflammation.