Are seed oils bad? In recent years, seed oils have become a topic of heated debate in the nutrition and health communities. Often vilified in popular health circles, seed oils are accused of contributing to inflammation, chronic diseases, and overall poor health. But are these claims backed by solid science?
This post aims to clear up the confusion and debunk the myths surrounding seed oils. By delving into the role of omega-6 fatty acids, reviewing the evidence on seed oils and inflammation, and examining why some studies report negative effects while broader research does not, we will provide a balanced, evidence-based perspective. My hope is that by the end you will understanding the true impact of seed oils on health.
What are seed oils?
Seed oils are edible oils extracted from the seeds of various plants. They are commonly used in cooking, baking, and as ingredients in processed foods. In home cooking in the UK, the most commonly found are rapeseed and sunflower oil. Some of the most well-known seed oils include:
- Rapeseed Oil: Extracted from the seeds of the rapeseed (or canola) plant, it is known for its light flavour and versatility in cooking.
- Sunflower Oil: Extracted from sunflower seeds, this oil is widely used for frying and as a salad dressing.
- Safflower Oil: Made from safflower seeds, it has a high smoke point, making it suitable for high-heat cooking.
- Soybean Oil: Derived from soybeans, this oil is a staple in many processed foods and is often used for frying and baking.
- Corn Oil: Made from corn kernels, it is commonly used for frying and in margarine.
- Cottonseed Oil: made from cotton plants
- Rice bran Oil: derived from the bran of the rice kernal.
- Grapeseed Oil: made form grape seeds leftover from the wine making process.
These oils are rich in polyunsaturated fatty acids (PUFAs), particularly omega-6 fatty acids. Seed oils are often chosen for their mild flavors, high smoke points, and affordability, making them popular choices in both home kitchens and the food industry. Sometimes, manufacturers won’t specify what type of oil is in the bottle. However, in the UK, most oils labeled as vegetable oil will be 100% rapeseed oil. (This will not always be the case with oils imported from countries – so do check the label for clarity.)
Why does the question are seed oils bad come from?
The argument against seed oils is that the high levels of omega-6 fatty acids promotes inflammation in the body. This is often quoted on social media to increase the risk of chronic diseases such as heart disease, arthritis, and other inflammatory conditions. Leading to the idea that all seed oils are bad for our health. But is this what the evidence says?
Let’s take a deeper look. Omega-6 fatty acids are a type of polyunsaturated fat. They are similar in structure to omega-3 fatty acids but have a double bond between carbon atoms at a different place on their molecular structure. There are several types of omega-6, but a commonly found example is linoleic acid. Linoleic acid is an essential fatty acid, which means our bodies cannot make it, we need it in our diets as it plays a key role in being part of cell membranes and in wound healing for example. Our bodies convert linoleic acid into a longer form called arachidonic acid, which is then converted into other compounds that may lead to inflammation. Here is where it gets a bad name and is said to increase inflammation in the body.
You may have heard of omega 3 fatty acids, also very important for our health. One key one is alpha linolenic acid which is converted in the body to anti-inflammatory compounds in the body. Let’s move on to think about this more.
Inflammation and omega-6 in seed oils
So why do we think omega-6 can cause inflammation and how does this lead to are seed oils bad? The compounds formed from linoleic acid in seed oils are pro-inflammatory whilst the compounds from alpha linolenic acid are anti-inflammatory. They’re very similar in structure and can be used in similar processes and they are made using the same enzymes. The theory is that too much omega-6 from seed oils will compete with the out-compete the omega 3’s leading to higher inflammation in the body. Thus increasing the risk of certain diseases.
That seems quite black and white then—if seed oils contain omega-6 fatty acids, and if those omega-6s are turned into inflammatory compounds in the body, then seed oils are bad, right? Luckily, things aren’t that simple. The problem with blanket-labeling foods as good/bad or anti-inflammatory/inflammatory is that it this lacks context. Several foods and compounds in our diet actually have the potential to both cause inflammation and reduce it. Plus inflammation is needed in some level in the body, it is how we fight disease and infection and injury.
Evidence Review: Seed Oils and Inflammation
Let’s take a look at seed oils and omega-6 to help us think about are seed oils bad. A recent systematic review of several studies found that eating more linoleic acid did not increase signs of inflammation in the body, but may even be linked to lower levels of inflammation. Another review shows that high intakes of linoleic acid actually reduces cardiovascular disease, improves glycemic control (bloods sugars) and may reduce the risk of developing type 2 diabetes. Showing that all you read on social media is definately not true!
Omega-3 and inflammation
One thing we do all seem to agree on is that omega-3 is anti-inflammatory. This means that including sources of omega-3 in the diet alongside omega-6 is a beneficial combination. But how much of each? Let’s go back to where we previously mentioned omega-3 and 6 being in competition. Because the compounds formed from omega-3 and 6 fatty acids are broken down by the same enzyme, they are essentially in competition to be metabolized into the body. If we eat more sources of omega-6, then in theory they will outcompete omega-3s, and omega-3s will take longer to be broken down. However, because omega-6 fatty acids might be less inflammatory than we thought, this competition is not quite as important. The relationship between omega-3 and 6 is a bit too complex to just say one is good and the other is bad.
The key takeaway here is that it is important to include omega-3 in the diet, but perhaps to not worry so much about ratios. Sources of omega-3 include:
- Oily fish
- Oysters
- Flaxseeds
- Chia seeds
- Walnuts
- Soy beans
- Hemp seeds or oil
- Supplements like algal oil, omega-3 rich cod liver oil
- Enriched foods like omega-3 enriched eggs
What about processed foods?
Part of the fear around seed oils is that they featured in ultra processed foods (UPFs). I’ve spoken quite a lot about UPFs on Instagram and TV, so do have a follow on there too. A diet that is high in UPFs and low in fruit and veg, fibre and healthier fats is more inflammatory than a balanced one that includes a variety of whole foods. Placing the blame solely on seed oils is missing the bigger picture. Seed oils, especially in the UK and EU, have strict food standards to make sure that they have not been processed in a way that could produce unsafe compounds.
Bottom line on seed oils
Understanding the true impact of seed oils on health requires a comprehensive look at the evidence. While seed oils contain omega-6 fatty acids, which have been linked to inflammation, the broader research indicates that these oils are not as harmful as some critics suggest. By maintaining a balanced diet that includes both omega-6 and omega-3 fatty acids, and by focusing on whole, unprocessed foods, you can enjoy the benefits of seed oils without undue concern.