Are seed oils bad for you?
Can seed oils such as rapeseed, sunflower and soybean have a place in a healthy diet? Find out what our nutritionist says
When people talk about seed oils, they are mainly referring to a list of eight oils derived from the seeds of plants. All eight are a source of fat and contain a relatively high proportion of omega-6 fatty acids, specifically linoleic acid. The charge against them is that, when heated, linoleic acid breaks down into pro-inflammatory compounds, and inflammation increases the risk of diabetes, depression, cardiovascular disease and cancer. But is this the case?
How are seed oils made?
The seeds are extracted dried, steamed and pressed to extract the oil. The extraction can be either a mechanical or chemical process. Mechanical pressing tends to preserve the natural flavour and nutrients of the oil. For large-scale production, chemical processing is favoured and critics claim seed oils that undergo chemical processing contain toxins, colourings and/or bleach.
Which seeds are used for oil?
The most common ones, also known as the ‘hateful eight’ are:
- Rapeseed (canola)
- Sunflower
- Soybean
- Cottonseed
- Corn
- Grapeseed
- Rice Bran
- Safflower
Discover our full range of health benefit guides and check out some of the best high fat foods to include in your diet.
Are we eating more seed oils?
There is no doubt that we are consuming more seed oils because they are used in a range of processed foods, cooking ingredients and even ‘healthy’ products that are now a main feature of our diets.
With changes in food production over the past 50 years, we have seen a steep increase in the amount of processed and ultra processed foods (UPFs). In fact, 57% of an adult’s daily energy intake derives from UPFs, with an even higher proportion seen in adolescents (66%). It’s these foods which are the main source of seed oils in the diet.
Foods that contain seed oils
Seed oils are commonly found in:
- Cooking oils: rapeseed, sunflower, soybean, corn and safflower
- Processed or packaged foods: crisps, crackers, frozen meals, biscuits, bread
- Fast food: seed oils are often used in deep-frying
- Margarine and spreads
- Salad dressings and mayonnaise
- Plant-based/vegan products: they use seed oils as a fat source
- Snacks: popcorn, granola bars and other convenience foods
Are seed oils toxic?
The chemical process which extracts the oils does include hexane (a solvent) – however, this is removed during processing and seed oils undergo rigorous safety checks to be used in foods. The concerns that they contain trans fats are outdated now, but ultimately the choice is down to the consumer as to which type of oil/fat they want to use.
Repeatedly heating unsaturated fats to high temperatures, such as in restaurant deep-fryers where oil is infrequently changed, is a health concern. However, cooking with seed oils at home to common cooking temperatures isn’t an issue.
What is omega-6?
The fats in seed oils are unsaturated and contain a specific type of fatty acid called omega-6. There are many different types of omega-6 fatty acids, but the one at the centre of the seed oil debate is linoleic acid. Linoleic acid is converted into arachidonic acid which is used in a variety of roles in the body. Some research suggests that this conversion is pro-inflammatory – which is a concern because high levels of inflammation are linked to increased risk of diabetes, depression, cardiovascular disease and cancer.
However, evidence suggests that increased intake of linoleic acid does not increase the concentration of inflammation after all. This study of almost 70,000 participants shows high levels of linoleic acid are in fact associated with lower risk of death from cardiovascular disease and death. Another study looked at linoleic acid and type 2 diabetes, which showed linoleic acid to be associated with lower risk. It is important to remember that inflammation does serve us in beneficial ways, too, and we need both kinds of fat (omega 6 and omega 3) in the diet.
Do seed oils cause type 2 diabetes?
Critics caution that seed oils cause disease, inflammation and diabetes. However the evidence does not stack up. There is a wide body of research stating that polyunsaturated fats, like omega 6 fatty acids, support health by lowering cholesterol and contribute to better blood sugar control.
This study found insufficient evidence to link omega-6 fatty acid intake and cardiovascular disease. Further analysis found that increased linoleic acid did not have any significant impact on inflammation while another study found it was associated with lower levels.
So, are seed oils bad for you?
While it’s true that many of the foods that use seed oils – such as processed snacks and fast foods – are unhealthy, they also tend to be high in refined carbohydrates, sodium and sugar. It is likely to be these components, not the seed oils themselves, which are the culprit behind weight gain and other negative health outcomes. Too much oil or fat from any source is not a healthy option, but there is no reason to remove seed oils altogether. Choose seed oils in moderation and don’t forget to include omega-3 fats and reduce the amount of UPFs when you can.
Further reading section:
5 ultra processed foods that are good to eat
Further information on forever chemicals
Top 10 anti-inflammatory foods
Follow this meal plan for cooking from scratch
Halloween party food
All health content on bbcgoodfood.com is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. If you have any concerns about your general health, you should contact your local health care provider. See our website terms and conditions for more information.
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