What’s in Your Edible Vegetable Oil?
FOOD, MEDICINE & HEALTH
The preponderance of scientific evidence supports the consumption of edible vegetable oils, which may reduce the risk of cardiovascular disease (DGA 2015). Edible vegetable oils such as palm oil, palm kernel oil, corn oil, soybean oil, canola oil, peanut oil, cottonseed oil, safflower oil, sunflower seed oil, and olive oil vary in their innate fatty acid composition (saturated, monounsaturated, and polyunsaturated). These fatty acid profiles may be affected when the oil is prepared for human consumption via winterization (removal of natural plant waxes) and deodorization (elimination of offensive odors).
Palm oil (~49% saturated, ~37% monounsaturated, ~9% polyunsaturated), which is derived from the pulp of the fruit of oil palms, has received considerable attention in the popular press (Bowerman 2017) and scientific community (EFSA 2016). It is an increasingly common cooking oil globally and is an important and functional ingredient in a broad spectrum of foods and cosmetics. Its use in the commercial food industry is widespread because of the high oxidative stability (saturation and possibly innate antioxidants) of the refined product when used for frying and its relatively low cost (USDA 2006, Che Man et al. 1999, Matthäus 2007).
In the past 10 years, there has been significant scientific and medical research into the cardiovascular health promotion effects of palm oil via replacement of industrial trans fatty acids (Lai et al. 2015). Palm oil, like all edible oils, has constituent fatty acids esterified with glycerol. The dominant saturated fatty acid is palmitic (~43%), and oleic acid (nearly 37%) is the primary monounsaturated fatty acid. Linoleic acid represents approximately 9% of the total fatty acid profile. Raw, unrefined palm oil also contains a range of bioactives: carotenoids (alpha-, beta-, and gamma-carotenes); sterols (sitosterol, stigmasterol, and campesterol); vitamin E (tocopherols and tocotrienols); and antioxidants, phenolic acids, and flavonoids (Edem 2002, Rink et al. 2011, Varatharajan et al. 2013, Wattanapenpaiboon et al. 2003).
Elevation of low-density lipoprotein cholesterol effects of the constituent palmitic acid are far less profound than with animal sources of this fatty acid because it is present predominantly in the sn1 and sn3 position as opposed to sn2 position as in animal fats such as lard. As such, palm oil, like other vegetable oils, including olive oil, has the favorable oleic acid in this position. Therefore, palm oil has been embraced as equally health promoting as olive oil (FAO/WHO 2008).
It is beyond the scope of this article to go into detail about the various other mechanisms that have been elucidated or proposed in explaining how palm oil may contribute to such effects as mitigation of reperfusion injury in cardiac tissue. Suffice it to say that palm oil is a versatile and rich source of nutrients, some of which may provide some health benefits, especially in the face of vascular lesions as demonstrated in animal models and cell studies (Ajiboye et al. 2015, Pacetti et al. 2016).
However, there has also been simultaneous scientific attention, and now escalating popular attention, on possible health risks associated with a class of process contaminants in palm oil (and in apparently lower concentrations in other edible oils) known as chloroesters or chloropropanols. A 2013 report by the European Food Safety Authority (EFSA) identified chloropropanols as heat- or acid-induced food contaminants created during the refining and decolorizing of all edible oils and some hydrolyzed plant-based proteins (EFSA 2013). Under high temperature and high pressure refining, chloride moieties that are extant can react with the glycerol backbone of lipids to produce 3-MCPD (Craft et al. 2012).
Inorganic chloride donors include the naturally occurring sodium chloride (likely derived from proximate seawater). Organic donors may arise from the use of fertilizers and insecticides (EFSA 2014). In March 2016, EFSA issued an extensive report warning about the possible health consequences of contaminants created during the processing of edible oils. EFSA specifically focused upon the demonstration of 3-MCPD (3-monochloropropane-1,2-diol), which has been classified as a possible human carcinogen since 2013 (IARC 2016).
Importantly, EFSA did not recommend dietary changes based on its findings, likely in light of the methodologic limitations of in vitro and rodent studies, the clustering of associated MCPD esters with a differential spectrum of absorption and metabolism, and the apparent capacity of certain cell lines either to potentiate or to reduce distribution and downstream effects of the putative toxicants. A paucity of uniform and long-term toxicity or carcinogenicity data likely also obviated dietary change recommendations. While selected European infant and follow-on formulas containing palm oil exceeded the established tolerable daily intake (2 ug/kg/day) of 3-MCPD, these levels were based upon projections from current consumption patterns and projected exposure scenarios, which may not accurately reflect actual intake. Thus, a number of potential threats to validity seem to have contributed to the EFSA report being provocative but also equivocating and confusing.
Confusion also stems from a history in which the stage was set for further concerns, and which now appears to impart even more gravity to the qualified research and opinions expressed in the most recent reports. In 2001, the United Kingdom’s Food Standards Agency (FSA) assayed various oyster sauces and soy sauces and found that that 22% of samples contained 3-MCPD at levels considerably higher than those deemed safe by the European Union. About two-thirds of these samples also contained a second chloropropanol called 1,3-dichloropropane-2-ol (1,3-DCP), which EU consultants advised should not be present at any levels in food (FSA 2009). On the basis of the limited, but worrisome, results of in vitro and animal tests, both forms of chloropropanols are thought to have the potential to cause malignancy in humans, and the agency recommended that the affected products be withdrawn from shelves and avoided. Yet there is an absence of any adverse effects of these substances in human studies.
While it may be concluded that the chloropropanols are potential hazards, their health risk remains poorly defined and is at least yet to be determined in any edible plant-based cooking oil. At this juncture, whether ultimately demonstrated as human toxicants or not, it will be necessary for collaborative efforts to explore and implement effective and cost-efficient approaches to mitigating the chloropropanol issue. The U.S. Food and Drug Administration addresses the issue in soy sauce and hydrolyzed vegetable protein (maximum 1 ppm). Whether or not valuable nutrients can coexist with clinically significant or insignificant toxicants ideally should depend upon scientific evidence, however, as in many other similar scenarios, the perception that a problem exists will require a dramatic response from the industry and regulatory agencies.
Roger Clemens, DrPH, CFS,
Contributing Editor
Adjunct Professor,
Univ. of Southern California School of Pharmacy,
Los Angeles, Calif.
[email protected]