Are seed oils harmful?

For patients seeking out nutrition advice on social media, they may have come across the advice to avoid all seed oils due to their ‘toxic’ and inflammatory effects. But is there any truth to this nutrition messaging? Here’s what general practitioners need to know.

What are seed oils?

Seed oils are the oils extracted from the seeds of plants and include canola oil, sunflower oil, corn oil, flaxseed oil, and grapeseed oil to name a few. Seeds oils contain both omega-3 and omega-6 fatty acids, and claims about any harmful effects is typically based on their omega-6 fatty acid content. It is true that for seeds oils, there is a higher proportion of omega-6 fatty acids, but does this make them ‘toxic’ or can they actually be beneficial for health? The evidence points to the latter.

Omega fatty acids

Omega fatty acids are essential, meaning that we must get them from our diet. Put simply, omega-3 fatty acids are anti-inflammatory and omega-6s can promote inflammation along with having other functions. However, this doesn’t mean omega-6 fatty acids are ‘bad’; they are both important for keeping the cardiovascular and immune system working properly and the key is having a good balance of both. However, a Western Diet tends to be very low in omega-3 fatty acids.

A closer look at omega-6s

What does the research say about omega-6 fatty acids? A Cochrane review of 19 randomised-controlled trials found that when more omega-6s were added to the diet, there was no increased risk of cardiovascular disease, and in fact, may even lower the risk of heart attacks [1]. Other studies have found that omega-6 supplementation was not associated with increased inflammation [2]. In fact, some studies have shown that people who have higher levels of linoleic acid (an omega-6 fatty acid) in their blood had a decreased risk of developing heart disease [3].

Additionally, food sources of seed oils are often packaged products that are ultra-processed and high in fats and sugars. So, a diet high in deep-fried foods is likely also high in omega-6s from seed oils, but it’s not the seed oils themselves that are harmful, but rather the foods they are found in.

The advice that seed oils are ‘toxic’ oversimplifies nutrition by focusing on a single nutrient. GPs can assure their patients that seed oils are safe to consume as part of a healthy diet and may in fact have health advantages in addition to being a cost-effective option for many. 

– Sarah Marko, Accredited Practising Dietitian

Learn more with HealthCert's online courses in Clinical Nutrition.

Read another blog like this one: Does weight dictate health?

References

[1]    Hooper L, Al-Khudairy L, Abdelhamid AS, Rees K, Brainard JS, Brown TJ, et al. Omega-6 fats for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev 2018. https://doi.org/10.1002/14651858.cd011094.pub4.
[2]    Ajabnoor SM, Thorpe G, Abdelhamid A, Hooper L. Long-term effects of increasing omega-3, omega-6 and total polyunsaturated fats on inflammatory bowel disease and markers of inflammation: a systematic review and meta-analysis of randomized controlled trials. Eur J Nutr 2021. https://doi.org/10.1007/s00394-020-02413-y.
[3]    Marklund M, Wu JHY, Imamura F, Del Gobbo LC, Fretts A, de Goede J, et al. Biomarkers of Dietary Omega-6 Fatty Acids and Incident Cardiovascular Disease and Mortality. Circulation 2019. https://doi.org/10.1161/CIRCULATIONAHA.118.038908.