Rapeseed Oil vs Olive Oil
Once only found in upmarket delis, rapeseed oil now stands on the shelves of most supermarkets. A pleasant seed-like and nutty taste and smell makes it a gourmet favourite. And its valuable nutritional profile, specifically canola oil, ensures that it is the cooking oil of choice among many nutritionists. Latest reports show that rapeseed oil is particularly beneficial for health, even more so than olive oil, recommended for the use whenever possible when preparing dishes. But, does it really warrant such high praise?
The allegedly excellent nutritional qualities of rapeseed oil are mainly based on its fatty acid profile. Comprising of large amounts of the omega-9 fatty acid oleic acid (around 60%), it also boasts high content of the omega 3 alpha-linolenic acid (around 11%) in an ideal ratio of over 1:2 with the omega 6 linoleic acid (around 19%). It is this high alpha linolenic acid content which seems to give rapeseed oil the edge over the omega 9 dominant olive oil. Alpha linolenic acid is converted in the body into the omega 3s EPA and DHA, with maximal conversion occurring when the omega 6 to omega 3 ratio is kept below 4:1. These fats are important for ensuring heart health in addition to brain health and controlling inflammation in the body. In one randomised controlled intervention trial, substituting dairy fat (which is mostly saturated) with rapeseed oil, reduced LDL cholesterol by 17% and triglycerides (blood fat) by 20% in patients with increased lipid levels after just three weeks.
However, the problem is that even when consumed in a vehicle of a low omega6: omega 3 ratio, alpha linolenic acid is an inferior version of omega 3, with poor conversions rates into the more desirable EPA (8-20%) and DHA (0.5-9%). And therefore, while rapeseed oil offers benefit in low omega 3 diets, and there are many of them out there, for the more health conscious individuals who are consuming adequate amounts of oily fish or fish oil/algae supplements, the consumption of rapeseed oil just because of its favourable omega 3 properties does not add much value.
The second health issue arises when using rapeseed oil for cooking. High temperature promotes a series of destructive chemical reactions such as hydrolysis, oxidation, isomerisation and polymerisation, forming compounds that in high concentrations can be harmful to our health. As a result, the health benefits of the oil may not be only diminished but even reversed. And the greater the polyunsaturated fat content, i.e. the greater its omega 6 and 9 content as found in rapeseed oil, the greater the tendency for these reactions to occur. Although rapeseed oil is known to have a high smoke point (the temperature at which the fats start breaking down, associated with the aforementioned destructive chemical reactions) and the conversion to harmful trans fats does not occur in a domestic setting, its overall thermal stability is low. This is particularly true of the nutritionally more valuable cold pressed, extra virgin rapeseed oil which is less stable than the processed rapeseed oil produced by solvent extraction. Olive oil, having a low polyunsaturated fatty acid content, seems a more thermally stable option, though, if cooking at high temperatures, especially with the extra virgin variety of olive oil, destructive chemical reactions will also occur.
In needs to be mentioned here that the stability of the oils is improved by their antioxidant content. Rapeseed oil is a rich source of the antioxidant vitamin E, mainly gamma tocopherol, while olive oil is rich in polyphenols. But, while these constituents help protect the fatty acids of the oil, their overall content is diminished, meaning the cooked oil offers a lower nutritional value.
The fact is that there is no single best oil for everything, a variety should be used. While rapeseed oil may not be recommended for use whenever possible, its pleasant flavour and taste, coupled with a healthful nutritional profile of a rich vitamin E source means that it has a place alongside olive oil in making cold dressings. For cooking, though, the more stable olive oil should be preferred. For high temperature cooking the best option is to choose a chemically stable, saturated fat product such as butter, goose fat or coconut oil just like generations before us used to do.