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Health Benefits of Rapeseed Oil

Rapeseed oil, also known as canola oil, is one of the most commonly used vegetable oils worldwide[1]. Certain sources promote several beneficial properties in terms of processing and nutrition. On the other hand there are sources that raise concerns, some of which are legitimate; but many are outdated or not applicable to edible rapeseed oil and its various uses.

How rapeseed oil is produced

Rapeseed oil is produced from the rapeseed crop, a member of the Brassicaceae family, which includes broccoli and cabbage. There are two main uses for rapeseed oil; as a food ingredient, and in various industries as a biodegradable lubricant and biodiesel. The rapeseed oil used in the food industry is significantly different from industrial rapeseed oil. This is to ensure it is palatable and safe for consumption at high concentrations[2]. Three different rapeseed crops can be used to make oil for human consumption: Brassica napus, Brassica rapa or Brassica juncea.

Rapeseed oil is light in colour with a relatively neutral flavour and is suitable for both frying and baking because of its high monounsaturated fatty acid content and smoke point. The smoke point is the temperature at which an oil begins to smoke; the higher the smoke point the less susceptible an oil is to oxidation and the more severe heat it can withstand before negative changes occur[3]. Rapeseed is also low in saturated fatty acids, hence its widespread use since the mid-20th century[1].

Nutritional composition

The composition of fats in rapeseed oil is approximately 62% oleic acid (a monounsaturated fatty acid), 19% linoleic acid, 9% alpha-linoleic acid and 7% saturated fatty acids[4]. Per 100g, rapeseed oils contain roughly 18mg of vitamin E and 71mg of vitamin K[5]. The amounts of other vitamins and minerals are minimal, if any[5].

Canola oil vs. Rapeseed oil

The name given to rapeseed oil that is suitable for use in food products is “canola” in North America. In the UK, rapeseed and canola oil are terms that are used interchangeably, more often rapeseed oil is used.

Canola oil was created in the 1970s in Canada using conventional plant breeding techniques[6]. These techniques selected varieties of rapeseed that had desirable qualities and bred them together, so the subsequent generations had a combination of these desirable characteristics. This resulted in a crop that was lower in erucic acid and glucosinolates, both of which are potentially toxic at high concentrations, and higher in the monounsaturated acid oleic acid.

Canola is a trademarked name and contraction of “Canadian-" and "-ola-", which means oil. To be able to call a rapeseed oil ‘canola oil’ the oil must contain less than 30 micromoles of glucosinolates and 2% erucic acid per gram of air‐dry, oil‐free solid[7].

The confusion around the content of erucic acid in edible rapeseed oil has created some of the myths that have led to a negative view of rapeseed oil. Rapeseed oil naturally contains 30-60% erucic acid, a compound associated with heart problems amongst other negative health effects[8]. Rapeseed oils for human consumption typically contain less than 0.5% erucic acid[9] and the Canadian Grain Commission reported an average erucic acid content of 0.01% in rapeseed and rapeseed oil samples from 2012 to 2018[10].

It’s been found that the contribution of rapeseed oil to the total dietary exposure of erucic acid is, in most cases, limited[11]. However, in a few dietary surveys, the consumption of rapeseed oil was a relatively high contributor with an average contribution of 39% in the dietary survey with the highest exposure estimate[11].

Roughly 90% of American and Canadian rapeseed is genetically modified (GM), mainly for herbicide-tolerance traits[12, 13]. This helps to protect the crop from disease and increase yield. Contrary to popular belief, only 25% of rapeseed crop worldwide is GM[14].

Types of Rapeseed Oil

Rapeseed oil is most commonly obtained from the seed by prepress solvent extraction[15]. A prepress step is required because rapeseeds are comprised of approximately 40% oil, double that of soyabeans, and so higher oil seeds require this additional stage[16]. Certain processing methods are viewed unfavourably with consumers so these steps will be discussed in more detail. Rapeseed oil, like other oils, can be bought after pressing without further extraction or refining. Unrefined rapeseed oil is higher in antioxidants but is more expensive and has a shorter shelf life compared to refined rapeseed oil[17].

Solvent Extraction

Pressing can’t remove all of the oil from the rapeseed. As a result, solvent extraction is used to extract the remaining oil from the solid material formed from pressing[15]. The selected solvent is hexane, which is highly volatile and has a low toxicity[16]. The toxicity worries some consumers who are not familiar with common food processes. Hexane has been used for nearly 100 years to extract plant oils and over 99% is recovered, which also reduces cost[18]. In one study, 40 samples of vegetable oil were tested, four had levels below detection and the other 36 all had levels of less than 1ppm, the EU limit[19]. The US has no detection limit for hexane in vegetable oils, most likely because it is not considered a significant issue[20]. Based on a worst case scenario it’s estimated that foods contribute 2% to the environmental exposure to hexane with vehicle fumes being the main contributor[21]. It’s evident that the trace amounts of hexane in food are not a health concern.

Refining

Refining consists of several steps which are important to achieve the desired shelf life and characteristics of most rapeseed oils[15]. Gums, waxes, phospholipids, free fatty acid, and colour pigments are removed to produce a clear liquid that does not readily oxidise. Bleaching is one of these steps and, due to its name, has negative connotations. However, no bleaches or chemicals are used, rather an acid-activated clay[22]. It’s an important procedure because it removes chlorophylloid compounds that catalyse oil oxidation and imparts an unwanted green colour[22].

Deodorisation is the final step in refining. Steam distillation is used to remove off-flavours, odours and heat sensitive colour pigments to produce a product that is acceptable for consumers[23]. There are some side-effects of this process. Deodorisation reduces the vitamin E and omega-3 content of the oil[24] and trans-fatty acids can be produced[23]. Over time this has resulted in the use of milder processing conditions to minimise trans-fat production and to maintain as much of the natural oil characteristics as possible.

Trans-fats

There was a push in the 20th century to use partially hydrogenated fats because they increased product shelf life, are semi-solid at room temperature so suitable for baking products and cheaper compared to the similar properties of animal fats and palm oil[25]. Partially hydrogenated fats are produced through industrial processing and are not naturally present in nature. These fats can be comprised of up to 60% trans-fats[26]. It was also thought that plant-sourced unsaturated trans-fats were better for health than animal sourced saturated fats[25]. We now know this is not the case[27].

The reason why trans-fats have multiple negative health effects is because they increase LDL (bad) cholesterol and triglycerides while decreasing HDL (good) cholesterol in the body[27]. This leads to an increased risk of cardiovascular diseases (CVDs) and death, with a possible increased risk of developing other chronic diseases too[27, 28].

Reduction and removal of trans-fats from food products started in 2003 in the EU. At the same time the World Health Organization (WHO) announced consumption of trans-fats should be below 1% of the total energy intake of the diet[29]. The US followed suit in 2015 when a ban on trans-fats being added or increased in foods, namely partially hydrogenated oils, was announced that came into force in 2018[30]. Consequently, studies based on oils and food products from the 2000s and before may be outdated due to product reformulation and changes by the food industry as a whole.

Refined vegetable oils, in particular rapeseed oil, as a source of trans-fats are often singled out. However, refined canola oil contains between 1-2% trans-fats whereas trans-fats can make up to 6% of the total fats of ruminant animal food products[31]. Considering this information, refined vegetable oils as a source of trans-fats are no longer the problem they once were.

Heating and Oxidation

Trans-fats can also be created outside of industrial processing. Contrary to popular belief, baking and frying at high temperatures do not significantly affect the amount of trans-fats in rapeseed oil[32]. The issue around trans-fats production is relevant to drastic heating conditions, such as the reuse of oil multiple times[33]. This most commonly occurs during commercial deep-fat frying operations such as with chips from fast food outlets[34].

What deserves greater attention is the formation of oxidation products, particularly harmful free-radicals during prolonged or repeated deep-fat frying. These processing conditions accelerate the rate of oxidation, which occurs at a much faster rate compared to exposure to the environment at room temperature[35]. Free-radicals can have a number of negative health implications including being atherosclerotic and increasing the risk of CVD[36]. Oxidation is less of an issue for rapeseed oil than other oils with a higher polyunsaturated fat content such as corn and soybean oil[32]. This is because polyunsaturated fatty acids are more readily oxidised than monounsaturated fatty acids. Refined rapeseed oils are also less susceptible to oxidation than unrefined rapeseed oils because components that are easily oxidised, such as free fatty acids, are removed during processing[17]. Due to the points mentioned above, repeated frying and prolonged exposure to the atmosphere should be avoided. Rapeseed oil should be stored in a cool, dark and dry place, such as a cupboard that is not next to an oven, in a sealed container.

Why Rapeseed Oil is Beneficial

Much of the confusion around whether rapeseed oil should form part of the diet tends to be around the issue of omega-6 fats being included in junk foods. Linoleic acid (LA), an omega-6 fatty acid, along with the omega-3 fatty acid alpha-linolenic acid (ALA) is essential in the diet. This means the body can’t produce these nutrients and so we must obtain them from food. This issue is covered in more detail in our article Health Benefits of Sunflower Oil. To summarise an important point from this article, the health effects of overconsuming heavily processed foods should not be confounded with a single ingredient. In the case of rapeseed oil, it’s high in mono- and polyunsaturated fats which have been shown to reduce the risk of CVD when they replace dietary saturated fats[37]. Additionally, rapeseed oil has a great omega-6:omega-3 ratio of 2:1[38]. Studies have suggested that a typical Western diet has an omega-6:omega-3 ratio of around 15:1 and adverse consequences occur with a ratio of above 10:1[38]. Read more in our Good Fats & Bad Fats article.

Rapeseed Oil in Huel Ready-to-drink

Huel Ready-to-drink includes rapeseed oil as an ingredient. This is to provide a good balance of unsaturated fats and help achieve a 2:1 ratio of omega-6:omega-3 fats. The total omega-6 content per 400kcal of Huel Ready-to-drink v1.0 is 3.3g and the total omega-3 content 2.1g. The rapeseed oil used in Huel is cold pressed, low in erucic acid and GMO-free.

References

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