Is canola oil toxic?
We lack research about canola oil being fed to dogs or cats -- this is a gap, but not an indictment
Canola oil has become an especially popular ingredient in human nutrition circles because of its heart-healthy message. This popularity has begun to migrate to petfoods with a few specialty products that contain canola oil. But, is adding this oil to petfoods wise?
Some mistaken websites contend that canola oil is toxic to man and animal alike. This is unequivocally false. Years of published studies in laboratory animals and humans have shown it to be nutritious and safe, and it is recognized as such by regulatory and health agencies around the world.
It is true, however, that we lack research about canola oil being fed to dogs or cats. This is a gap, but not an indictment. In the absence of direct evidence, maybe a bit of background would be beneficial in order to dispel the myths and provide an understanding of whether canola oil has a place in pet nutrition.
A checkered past
Canola oil wasn't always in vogue. It owes much of its newfound popularity to a name change, along with decades of hard work by researchers, plant breeders, growers and trade associations. In the years leading up to, and during, World War II, canola was known solely as rapeseed. A member of the Brassica family, canola/rapeseed is related to turnips, cabbage, mustard, broccoli and brussel sprouts.
Rapeseed, the progeny of Brassicus campestris (a seed variety) and Brassicus napus (a forage variety), was originally grown for its oil. This oil had a high content of erucic acid (an omega-9 fatty acid) that made it an effective industrial lubricant important to the war effort. Unfortunately, consumption of rapeseed by livestock led to an enlargement of the heart and poor performance as a direct result of erucic acid.
The hull from the rapeseed was also high in lignified fiber, which was poorly digested and contained a goitrogenic (thyroid enlarging) glucosinolate (glucose-amino acid compound). These negatives made rapeseed unsuitable for food or feed. This was a real challenge following the war as many temperate areas of the world where rapeseed had been grown no longer had a market for their crop, and few alternatives such as soybeans or corn were adapted to the climate or growing season.
Plant breeders to the rescue
Varieties low in erucic acid and glucosinolates (the so-called double low cultivars) were developed using classic plant breeding techniques. But, as current myths demonstrate, the negative connotations associated with rapeseed's name persisted. So, a name change was in order. The new name "canola" is a conjunction of "Canada oil low acid," which aptly describes the location and outcome from breeding efforts.
To assure this carries through to the consumer, there are standards for what qualifies rapeseed as canola. In the US, canola is defined as "seeds of the genus Brassica from which the oil shall contain less than 2% erucic acid in its fatty acid profile and the solid component shall contain less than 30.0 micromoles of any one or any mixture of 3-butenyl glucosinolate, 4-pentenyl glucosinolate, 2-hydroxy-3-butenyl, or 2-hydroxy-4-pentenyl glucosinolate, per gram of air-dried, oil-free solid" (US Code of Federal Regulations).
Canola oil is rich in oleic acid (an omega-9 fatty acid that is about 60% of the oil), has significant levels of the essential linoleic acid (an omega-6 fatty acid that is about 19% of the oil) and beneficial levels of the omega-3 linolenic acid (9% of the total). The oil is also reported to be rich in vitamin E (alpha and gamma tocopherols), vitamin K (as K1; phylloquinone) and have measurable levels of phytosterols such as stigmasterol, campesterol and beta-sitosterol (US Department of Agriculture, 2009). There are also specialty varieties with elevated levels of oleic acid (70%) to improve shelf life, or enriched with gamma-linolenic acid (GLA, a special omega-6 fatty acid) as an option to borage or evening primrose oil.
Canola oil inclusion in the diets for people and experimental animals has been reported to lower cholesterol, inhibit cardiac arrhythmias, lower blood pressure, reduce body fat composition and improve weight control as a result of its low content of saturated fatty acids and elevated levels of mono- and poly-unsaturated fatty acids. While interesting, these heart-healthy factors would not be the prime motivators for inclusion in pet diets.
Canola oil in a pet diet contributes a significant amount of the essential nutrient linoleic acid. With its content of linolenic acid, it helps narrow the ratio of these two fatty acids to a level consistent with the values suggested by the US National Research Council (2006). Any concern that canola oil, with its abundance of monounsaturated oleic acid, could impede the production of anti-inflammatory mediators is unnecessary.
From a formulation perspective, canola oil is commonly used in home-made "elimination diets" (used to identify and eliminate allergens )partly because of its novelty to the pet but also because of its availability to pet owners. In these applications, no reports of issues with acceptance or adverse reactions have surfaced in the veterinary community. In other specialty diets, canola oil is often requested for addition as a dietary option, i.e., instead of animal or poultry fat.
In comparison to animal and poultry fats, canola has a comparable to higher level of linoleic acid and also brings along some omega-3 fatty acids. So, it can be a reasonable option in these circumstances. However, as noted previously, what we know about feeding canola oil to dogs and cats is an extrapolation from other species at this stage. While all logic would suggest that this is a safe and nutritionally effective option for our petfoods, there would be real value in confirming this with dog and cat validation studies.