Vegetable oil gets a really bad rap but is its poor reputation justified? Does it really cause inflammation and oxidative stress? Or, like olive oil, can it be a healthy addition to your diet? One of the most common and easily available vegetable oils is rapeseed (canola in the US, and often sold as generic ‘vegetable oil’) so here we address five of the biggest myths about the edible oil.
Myth #1: Vegetable oil raises cholesterol and risk of cardiovascular disease
We’ve all heard that olive oil is a heart-healthy fat, but some are concerned that the consumption of vegetable oil can raise our cholesterol and risk of heart disease. However a large meta-analysis of 42 clinical trials looking at the effects of rapeseed oil on many different health factors found that it performed much like olive oil. However, when compared to saturated fat from butter, three markers of heart health that may indicate a higher risk for disease (LDL-C, Apo B and triglycerides) were all lowered in the group consuming rapeseed oil. So, although olive oil is often touted as the healthiest oil, rapeseed oil is right up there when it comes to lowering cholesterol and improving heart health. Although many studies don’t state whether they are using refined or cold-pressed oil, in those that do, even refined oil had heart-healthy effects.
Myth #2: Vegetable oil reduces insulin sensitivity and increases diabetes risk
Our body needs to produce insulin to turn food into energy and control blood-sugar levels. When our body can’t produce and regulate insulin, we develop diabetes. Research has shown that some fatty foods, like lard, can increase the risk of type-2 diabetes, however this is not true of rapeseed oil. Rapeseed oil does not have any negative impact on our body’s ability to metabolise glucose but some studies (here and here) suggest it may have a positive effect when compared to saturated fat. One study found that even refined rapeseed oil improved fasting insulin and insulin resistance – with over 400 calories a day coming from canola oil alone! Although we wouldn’t recommend having this much fat in your diet.
Myth #3: Vegetable oil causes oxidative stress
You may have heard that cooking with vegetable oils causes the oil to oxidise, contributing to oxidative stress in the body. Oxidation is a process in which a chemical substance changes because of the addition of oxygen. However, studies have shown (here and here) that when rapeseed oil is used to cook, it does not increase oxidation in humans. Unsaturated fats do oxidise when exposed to heat but they also contain antioxidants, such as vitamin E, which may counter any bad effects when we consume it. Oxidation increases with temperature and time heated, so it’s not be good to reheat oil again and again – as many fast food restaurants do – but using a small amount, below 200 degrees celsius, shouldn’t be a problem.
One disease linked to oxidation is cancer. But a large study found that people cooking with rapeseed oil actually have a lower risk of dying from cancer (and respiratory disease and infection) than those cooking with butter. This adds further evidence that the small amount of oxidation that occurs in heated rapeseed oil doesn’t have the same negative health effects as animal fats.
Myth #4: Vegetable oil causes inflammation
One of the biggest misconceptions about rapeseed oil is that it causes inflammation. The aforementioned meta-analysis of 42 clinical trials also looked at markers of inflammation and found no significant effect of consuming vegetable oil on inflammation.
Rapeseed oil contains omega-6 fats, which are healthy when consumed in moderate amounts. However, most people get too much omega-6 fat in their diet and too little omega-3, which can lead to inflammation. Fortunately, rapeseed oil has an omega-3 to omega-6 ratio of 1:2, making it a good option. Most experts agree that a 1:4 ratio or less is best for good health, meaning that you should aim to eat one gram of omega-3s for every four grams of omega-6.
Myth #5: Vegetable oil leads to weight gain
You might assume that as rapeseed oil is almost all fat, it would lead to weight gain. However, a meta-analysis of 23 randomised control trials found that compared to saturated fat (like butter) the consumption of rapeseed oil actually reduced body weight by a small but significant amount in participants with type-2 diabetes. Even though in many trials the weight loss was often small, we can at least say that canola oil doesn’t increase body weight. Of course, because any oil is calorie-dense, if you add it on top of what you are already eating you will gain weight purely because you’re consuming more calories.
Rapeseed and olive oil may not only help reduce fat around the belly but around the liver too and may even help reverse non-alcoholic fatty liver disease (NAFLD). In one study, over 76 per cent of participants with NAFLD reverted to normal liver function after six months of consuming 20 grams (1.5 tablespoons) of rapeseed oil a day instead of their usual refined oil.
So, as you can see, rapeseed oil, rich in poly- and mono-unsaturated fats, rather than being a health hazard can actually be a healthy addition to the diet – as long as you’re not glugging bottles of it but using it in moderation to dress salads and sauté healthy foods. In most of these studies, participants were only consuming between one to four tablespoons of rapeseed oil a day so the results certainly don’t justify deep-frying food or filling up on ultra-processed junk foods which may contain some vegetable oil but also a multitude of hidden health-harming ingredients.