Evidenced-based critique and evaluation of omega-6 plant-based oils
Table of Contents
Omega-6 and Inflammation Explained
Trans-Fats & the Hydrogenation Process
Summary
This review article aims to present and critically evaluate the safety and health-related properties of omega-6 rich oils in the marketplace. It will compare and contrast popular seed oils and present potential health-related outcomes.
The industrialization of vegetable seeds began in the 1920’s for the sole purpose of reducing the cost of vegetable oil production. Refined oils such as soybean and corn are rich in omega-6 polyunsaturated fatty acids which when mixed with excess insulin deriving from cheap carbohydrates can lead to increased production of toxic fat (Sears, 2008). All grains and starches comprise pure glucose held together by very weak chemical bonds which can be broken during digestion. The released glucose rapidly enters the bloodstream causing the release of the hormone insulin. Increasing levels of insulin promote omega-6 from vegetable oils to produce more arachidonic acid the biochemical precursor to powerful inflammatory hormones called eicosanoids (Sears, 2008). Soybeans and corn are also processed using hexane, a constituent of gasoline as an extracting solvent and the mass intake of these industrially produced vegetable oils has increased over a thousand-fold during the last century with implications for human health (Blasbalg et al., 2011).
The increased consumption of omega-6 fatty acids via the excessive intake of cheap, refined vegetable oils, and simultaneous decrease of omega-3 is well documented with implications for human health (Elagizi et al., 2021). Industrialised seed oils are considered a key culprit for disease risk increase and the refining process markedly decreases the nutritional content of the oil, e.g., essential fatty acids, vitamins and antioxidants (Aniołowska et al., 2016; Gharby, 2022; Wroniak & Rękas, 2016). In addition, factory farms which is the modern industrialised method for raising livestock are frequently fed soybean oil pellets which contributes to elevated omega-6 in human consumption[1]. The main ingredient in soybean is the omega-6 LA, which is head of the omega-6 family of PUFAs. Through various biochemical processes, an excessive intake of omega-6 can increase risk of inflammation which is discussed further in the next section.
Omega-6
Omega-6 polyunsaturated fatty acids (PUFAs) are dietary essential. At the top of the omega-6 series is linolenic acid (LA, c18:2n6) which is a metabolic precursor to gamma-linolenic acid (GLA, c18:3n6) and then arachidonic acid (AA, c20:4n6) connected biochemically via an elongase and 2 desaturases. AA is a powerful bioactive molecule and when released from membrane phospholipids is converted to a variety of compounds called eicosanoids, known to be involved in the resolution of inflammation and tissue homeostasis.
Although, there is a strong and long withstanding academic focus on the health promoting effects of omega-3, in 1982, Nobel prize winners Bergstrom, Samuelson and Vane, documented the properties of arachidonic acid (AA) in particular, their oxidative derivatives which assisted in the functioning of blood flow, the control of blood pressure, and inflammation in the resolution of injury (Crawford et al., 2023; Higgs et al., 1986; Samuelsson, 1986).
The critical message regarding omega-3 and omega-6 fatty acids is that the balance of both is essential and, that an imbalance is thought to have negative health impacts, including increased inflammation. Balancing intake of these PUFAs, is important to establish healthier dietary patterns and to reduce and prevent obesity (Albar, 2022; Gibbs & Cappuccio, 2022). Oils containing omega-3 are widely considered to be beneficial and the inclusion of for example chia seed oil which is rich in α-linolenic acid is associated with a range of health benefits including decreased blood glucose, decreased waist circumference and weight in overweight adults, and improvements in skin (Parker et al., 2018).
Omega-6 fatty acids compete with omega-3 polyunsaturated fatty acids to acquire space in human cells (Innis, 2014). A Western-type diet (e.g., refined, ultra-processed, supermarket foods) increases intake of omega-6 to unhealthy levels, e.g., between 12–17 grams of omega-6 daily. This has consequences also for the balance and ratio of omega-3 and omega-6 in the brain, with the latter acquiring more of the space (Artemis P. Simopoulos, 2016). A healthy balance of omega-6 to omega-3 is estimated to be similar to the palaeolithic diet of our ancestors, namely, 2:1 or 1:1 (the optimal balance for brain health). However, recent estimates suggest that this ratio in those consuming Western-type diets rich in soybean oil (e.g., processed foods and refined, vegetables oils) is in the region of 20:1 omega-6/omega-3 (Albar, 2022; Simopoulos, 2002; Artemis P. Simopoulos, 2016). This is not to dispute the importance of omega-6 for the brain – all cells require it – but it is the balance that is critical. Inflammation is the body’s way of altering us to injury – a signal to tend to a wound and to help the healing process of bodily tissues.
Omega-6 fatty acids are considered highly prothrombotic and pro-inflammatory and an excess of them in modern Western diets has implications for disease risk (Torres-Castillo et al., 2018). Furthermore, the biochemical imbalance of omega-3 and omega-6 in the brain is theorized to have contributed to the worldwide pandemic of non-communicable disease such as the premature development of metabolic health conditions including obesity, inflammatory bowel disease and Type 2 diabetes (Liput et al., 2021; Schreiner et al., 2020; Artemis P. Simopoulos, 2016; Torres-Castillo et al., 2018). The obesity epidemic has implicated an excess of omega-6 fatty acids as a key contributing factor (Artemis P. Simopoulos, 2016). In addition, correcting the balance and increasing omega-3 intake may assist chronic disease including non-alcoholic fatty liver disease (Elagizi et al., 2021; Parker et al., 2012).
Clinical trial research outcomes suggest that diets low in omega-3 fats and high in omega-6 fats are linked to higher levels of neurodevelopmental deficits, poor cognitive performance, child aggression/antisocial behaviour, violent crime, homicide and suicide (Gow & Hibbeln, 2014; Hibbeln, 2009; Hibbeln & Gow, 2014; Raine et al., 2021). Therefore, the balance and ratio of these PUFAs in food products is critical for human health.
Omega-6 and Inflammation Explained
Scientific research has demonstrated that there is a high volume of omega-6 polyunsaturated fatty acids (PUFAs) in cell membranes which are involved in inflammation. It has also been demonstrated that an elevated dietary intake of omega-6 fatty acids is associated with inflammation, this is because the omega-6 arachidonic acid (AA) is the biochemical precursor to potent pro-inflammatory lipid mediators namely prostaglandins and leukotrienes. There are some studies suggested that omega-6 fatty acids may not lead to inflammation and the extent to which omega-6 fatty acids are implicated in the inflammatory process is a rigorous topic of ongoing debate and investigation (Innes & Calder, 2018).
Inflammation is without a doubt, a necessary process which forms a critical part of human defence and tissue healing. It protects the human host and also prevents insult from pathogens (Calder et al., 2013). However, prolonged, excessive or unresolved inflammation can lead to tissue damage, and pathological disease development (Innes & Calder, 2018). The omega-6 PUFA, arachidonic acid (ARA) is responsible for a proportionate amount of the fatty acids present in the membrane phospholipids implicated in inflammatory processes. There are also additional factors such as age, body type (e.g., overweight or obese) and diet which can alter the amount of an inflammatory marker at any given time (Calder et al., 2013). The resolution of inflammation is discontinued once the infection or injury is eliminated. This process enables an active process by which certain mediators are down-regulated to disable processes which were previously activated (Calder et al., 2013). Chronic inflammation may persist if failure to resolve the process persists and exposure to the triggering agent continues (Calder et al., 2013). The role of diet and specifically ultraprocessed foods as a driver of inflammation is a topic of substantial scientific interest. The correct identification of biomarkers of inflammation such as inflammatory cytokines are necessary to influence and reverse the process and limit further damage to the host (Calder et al., 2013). The control of inflammation is vital to maintain human health and homeostasis, and, importantly to prevent pathological disease development (Calder et al., 2013).
Borage oil
Borage oil is manufactured by extracting oil from the seeds of the Borago officinalis plant. The borage plant is indigenous to the Mediterranean and North Africa and known for its attractive, star-shaped blue flowers, the petals of which are edible. Borage oil is naturally rich in gamma-linoleic acid (GLA) which has anti-inflammatory, anti-fungal and anti-bacterial properties. Borage oil also contains mineral salts, Vitamin C, flavonoids, magnesium, potassium, zinc and iron. It is also considered a diuretic which can help remove toxins from the body. Due to its GLA content, borage oil has anti-inflammatory effects (Belch & Hill, 2000). The are many potential health benefits associated with its use including helping to alleviate skin conditions such as acne, eczema and rosacea (Brosche & Platt, 2000; Lin et al., 2018), wound healing and repair of the skin barrier (Lin et al., 2018). Borage oil may also help ease premenstrual and menopausal symptoms, and reduce inflammation and inflammatory conditions such as rheumatoid arthritis (Reed et al., 2014). Borage oil may have a role in heart health[2] as well as additional potential in lowering blood pressure (Engler & Engler, 1998) and cholesterol levels while supporting immune system functioning (Al-Okbi et al., 2018; Maldonado-Menetti Jdos et al., 2016; Tewari et al., 2019).
Gamma Linolenic acid (GLA) is an omega-6 essential fatty acid which is sourced from certain nuts, seeds and vegetable oils, e.g., borage and evening primrose oil. The human body converts GLA to prostaglandin E1 (PGE1) which is often used as a medication. It is commonly known as a vasodilator due to its ability to widen blood vessels and relax smooth muscles[3]. The potential therapeutic use of GLA can be traced back for centuries and its inclusion in folk medicine and homeopathic remedies, often referred to as the king’s cure-all. Although, much of the potential health claims lack credible scientific evidence and are anecdotal. Furthermore, consumption of borage oil is generally recognised as safe, however there are some documented cases of seizures (Al-Khamees et al., 2011) and possible liver health effects.
Sunflower oil variations
Sunflower oil is manufactured by pressing the seeds of the sunflower (Helianthus annuus) plant. It is often considered to be a healthy oil due to its content of polyunsaturated fatty acids however potential health benefits will vary according to the type of oil and its nutrient composition. Conversely, an excess intake of sunflower may be linked to potential health harm. There are approximately 4 different types of sunflower oil available in the commercial marketplace which are uniquely modified to yield differing fatty acid compositions. Sunflower oil ranks fourth behind palm, soybean, and canola in terms of the worldwide production of nine major vegetable oils (List, 2017). Traditional sunflower oil has a composition high in polyunsaturated fatty acids (e.g., circa 70%) making it attractive to consumers for consumption. However, regular sunflower oil lacks high temperature stability as a deep fat frying oil and to compensate for this plant breeders and plant geneticists introduced different variations into the commercial marketplace which included mid-oleic (65% oleic acid) and high oleic (82% oleic acid) (List, 2017). These modified sunflower oils have improved oxidative stability in high temperature applications and a long shelf life (List, 2017). Other versions include high stearic/high oleic (72% oleic acid, 18% stearic acid) and high linoleic acid (around 68% LA) (List, 2017).
The high oleic acid version of sunflower oil is arguably the healthier option with a composition of around 82% omega-9 oleic acid. Omega-9 oleic acid is a monounsaturated fatty acid with one double bond in its carbon chain. High oleic acid sunflower oil contains around 120 calories per 1 tablespoon (15 ml) serving, 14 grams of total fat, 1 gram of saturated fat, 11 grams of monounsaturated fat and 0.5 grams of polyunsaturated fatty acids. The purported health benefits of sunflower oil are attached to those rich in oleic acid (e.g., 80% oleic acid +). A small comparison study reported that participants consuming a diet rich in high oleic sunflower oil for 10 weeks had significantly lower LDL cholesterol and triglycerides than controls (Allman-Farinelli et al., 2005). Another small study reported increases in HDL (good) cholesterol in participants consuming a high-oleic acid diet for 8 weeks compared to a diet without sunflower oil (Jenkins et al., 2010). High oleic sunflower oil may help support heart health, however more research is needed to be conclusive. The high stearic/high oleic sunflower oil version also contains stearic acid, a saturated fatty acid which is stable at room temperature and is used for various culinary purposes.
The high LA sunflower oil version comprises elevated amounts of LA in the region of 68%. Exposing sunflower oil to temperatures of 180°F (82°C) may also release toxic compounds such as aldehydes which are linked to potential damage to DNA and cells and may also contribute to neurodegenerative disease and heart disease (LoPachin & Gavin, 2014).
In relation to content, sunflower oils do not contain protein, carbohydrates, cholesterol or sodium. They comprise 100% fat and health-beneficial, antioxidant vitamin E. The high LA version contains around 120 calories per 15 mL serving, 14 grams of fat, 3 grams of monosaturated fatty acids, 9 grams of polyunsaturated fatty acids (PUFAs) and 1 gram of saturated fats. The mid-oleic contains the same number of calories, total fat and saturated fat but 8 grams of monounsaturated fatty acids (MUFAs) and 4 grams of PUFAs. The high oleic sunflower oil version contains the same amount as the other 2 types in relation to calories, total fat and saturated fat, but contains the highest amount of MUFAs (11 grams) and only 0.5 grams of PUFAs. An abundance of research supports the notion that it is the balance of PUFAs which are important in reducing cardiovascular disease risk factors (Binkoski et al., 2005). The varieties of sunflower oil which are high in the omega-6 LA are least favourable due to their potential inflammation raising properties (Jandacek, 2017) and a balance of omega-6 and omega-3 is thought to be critical to reduce disease risk (Simopoulos, 2008). Sunflower has been found to release the highest volume of toxic aldehydes when exposed to high heat over extended periods in comparison to other oils (Moumtaz et al., 2019). In conclusion, sunflower oil may be tolerable in small amounts, but some varieties are linked to elevated levels of omega-6 LA and so should be restricted for use in lower heat applications. Other oils such as olive, avocado and rapeseed are arguably healthier alternatives and more stable during cooking.
In summary, the high stearic/high oleic version of sunflower oil[4] (as opposed to the high-LA type which should be avoided) is considered to be healthier than many other commercial, industrially available seed oils. It can also be used in dairy products such as ice-cream. Consuming oleic acid over omega-6 rich oil in moderation is considered preferable for use in food products in terms of overall health due to its anti-inflammatory, heart-healthy, skin-promoting effects. There is ongoing debate concerning the use of fats based on stearic acid as a potential healthier alternative to existing oils, arguably the key concern is the mutagenesis and breeding of the oil crop (Salas et al., 2014). There is no doubt, that the MUFAs and PUFAs present in high oleic sunflower oil are beneficial. Furthermore, a high oleic acid sunflower oil is more stable for cooking.
Corn oil
Corn undergoes a complex process to produce corn oil which is widely used in cooking especially deep frying. Corn is not a naturally oily food, and the kernels are separated to mechanically produce the oil via a series of synthetic processes including hexane extraction, deodorization and winterization. The oil from corn is also used for industrial purposes as a fuel for gasoline and diesel-powered engines, as a cleaner, lubricant and as an ingredient is cosmetic products. Corn oil comprises one hundred percent fat and one tablespoon of corn oil (around 15 ml) contains 14 grams of fat, approximately 13% of the recommended daily intake of Vitamin E and 122 calories. Corn oil is made up of between 30%-60% linolenic acid an omega-6 polyunsaturated fatty acid. As discussed in previous sections, the balance of omega-6/3 is critical for the maintenance of human health (Gómez Candela et al., 2011). The pro- and anti-inflammatory effects of omega-3 and omega-6 are well documented, and an imbalance of these essential fatty acids is implicated in cardiovascular disease and metabolic syndrome (Tortosa-Caparrós et al., 2017). The ratio of corn oil is imbalanced in relation to our dietary requirements, at 46:1, higher than the recommended ratio of 4:1 omega-6/omega-3. Corn oil has a very high smoke point of about 450 °F or 232°C making it popular for deep-frying. Corn oil has a high phytosterol content in comparison to other cooking oils (Mo et al., 2013). Phytosterols have been found to reduce cholesterol absorption and LDL-cholesterol concentrations, however very little is known about phytosterols sourced from commercially available corn oil and other vegetable oils in relation to their impacts in human health (Howell et al., 1998; Ostlund et al., 2002). The three main compounds which are linked to human health include linolenic acid (but balance is critical), the powerful antioxidant, vitamin E and phytosterols. An intake of polyunsaturated fatty in comparison to saturated fat intake has been found to be superior for the prevention of cardiovascular disease risk in a meta-analytical review study published in 2014 (Farvid et al., 2014). Some of the smaller studies demonstrated beneficial findings in relation to corn oil intake are funded by the corn oil industry (e.g., ACH Food Companies, Inc., the producer of Mazola corn oil) and should be interpreted with caution due to potential publication bias. Furthermore, GMO corn is often treated with weed killers, such as Roundup – the chemical herbicide containing glyphosate[5]. The World Health Organization (2015) declared glyphosate as a probable carcinogen. Furthermore, there is some evidence to suggest that it is possibly linked to an increase in food intolerances and allergy rates (Gotua et al., 2008; Samsel & Seneff, 2013; Spök et al., 2005). Overall, arguably further research is needed to draw firm conclusions about its use in the commercial marketplace but due to its GMO status coupled with the known imbalance of omega-6 to omega-3 (46:1) (and well-documented detrimental impacts to metabolic health) it is not recommended for use in any food products.
Safflower oil
Safflower oil is manufactured via the safflower plant (Carthamus tinctorius L.) which is a member of the Asteraceae family or sunflower family. The oil is made from the seeds of the safflower plant which is thistle like and originates from countries including Iran, India, Egypt and China, although is cultivated globally. There are 2 main types of safflower oil namely high-linoleic which contains higher amounts of polyunsaturated fatty acids and high-oleic safflower oil which is rich in monounsaturated fatty acids. The high-linoleic version contains approximately 70% linoleic acid with just 10% monounsaturated fats in the form of oleic acid. Safflower contains around 14 grams of fat per 1 tablespoon of oil. It has very little nutritional value other than containing around 32% of the recommended daily value of Vitamin E. Both oleic and linoleic acids make up around 90% of safflower oil. The saturated fats stearic acid and palmitic acid make up the remaining 10%. However, the amounts of linoleic acids and oleic acid in safflowers seeds varies considerably resulting into the two types. The high-oleic safflower oil version tends to be more commonly utilised in the commercial marketplace because it has a higher smoke point 232°C or 450°F compared to other seed oils such as canola oil. Safflower oil has little evidence supporting its use as a healthy oil aside from its Vitamin E content. Vitamin E is highly beneficial and necessary for correct function of the immune system, as well as containing beneficial antioxidants. Vitamin E can be found naturally occurring in spinach, almonds, sunflower seeds, fish and avocados and in sufficiency is rare in healthy individuals. The primary component of safflower oil is the omega-6 linoleic acid (LA) and excess intake of omega-6, LA is linked to potential harm including increasing risk of inflammation in the brain (Taha, 2020). Conversely, other studies suggest the LA may help reduce cholesterol however, it is generally agreed that the amounts of LA consumed daily in the Western population are too high (Jandacek, 2017). Further studies of the effects of high LA diet are required in humans to fully extrapolate the mixed and often confusing findings.
Soybean oil
Soybean oil is a vegetable oil which has been extracted from the seeds of the soybean plant. The consumption of soybean oil during the 20th century has increased over a thousand-fold and is thought to have attributed to the declining human tissue compositions of omega-3 EPA and DHA (Blasbalg et al., 2011) and potential rise in metabolic health disease risk. Its elevated inclusion in Western-type diets grew as a result of agricultural shifts in the 1930’s accounting for at least 7% of daily calories (although that data does not reflect the growth between 2011 to the present time in 2023) (Blasbalg et al., 2011). Furthermore, during 2018-2019 alone, approximately 62 million tons (56 million metric tons) of soybean oil were produced globally rending soybean oil as one of the most widely-used cooking oils in the marketplace[6]. The average ratio of omega-6 to omega-3 has elevated from as little as 1:1 or 4:1 to as much as 30:1 (Simopoulos, 1999; A. P. Simopoulos, 2016). The omega-3 index, which is the sum of erythrocyte EPA + DHA as a percentage of total fatty acids, is widely employed as a risk biomarker for cardiovascular disease (and more recently evaluated in relation to risk of psychiatric disease) in both clinical and research applications (Harris, 2008; von Schacky, 2014). It is thought that the majority of omega-6, LA intake in the United States alone comes from consumption of products containing soybean oil (Taha, 2020). Pre-clinical evidence indicates that overabundance of dietary LA elevates the brain’s vulnerability to inflammation and is anticipated to influence its oxidized metabolites. In human studies, elevated maternal LA intake has been associated with atypical neurodevelopment, but underlying mechanisms remain unclear. There is a general consensus that excess dietary LA may adversely affect the brain. The potential neuroprotective role of decreasing dietary LA warrants clinical appraisal in future studies (Taha, 2020). LA is also a precursor to oxidized products known as oxidized linoleic acid metabolites (OXLAMs). These are lipid mediators known to regulate pain and inflammatory signalling in peripheral tissue and are abundant in the brain (Patwardhan et al., 2009; Ramsden et al., 2017; Schuster et al., 2018; Taha, 2020; Warner et al., 2017). Research conducted in the late 1950’s and 1970’s demonstrated that chicks fed a vitamin deficient diet containing the omega-6 LA developed a serious neurodegenerative condition called encephalomalacia which can create a range of anomalies such as necrosis and lead to death (Taha, 2020; Wolf & Pappenheimer, 1931).
Soybean oil is rich in omega-6, LA with known proinflammatory effects. It is also linked to metabolic and neurological alterations in animal studies and excess use may contribute to poor metabolic health and increased inflammation – all of which are implicated in Type 2 diabetes and obesity as well as poor mental health (Deol et al., 2020).
Soybean oil has a high smoke point of around 450 °F or 230 °C during which fats are broken down and start to oxidise which results in the formation of harmful compounds called free radicals (also known as environmental pollutants) which create oxidative stress in the body and are implicated in disease and degeneration of the body and brain (Perumalla Venkata & Subramanyam, 2016). Animal studies have demonstrated that heated soybean increases markers of both oxidative stress and inflammation (Miyamoto et al., 2018).
Soybean oil is rich in vitamin K which may support bone health and also contains a small amount of plant-based, omega-3, alpha-linolenic acid (ALA) in each serving. Although, the conversion of ALA into heart and brain healthy EPA and DHA is considered rate-limiting and inefficient, i.e., less than 0.1-7.9% of ALA is converted into EPA and >0.1-3.8% of ALA to DHA. Soybean oil is therefore not a reliable source of omega-3 nor recommended for a direct source of DHA and EPA which are critical for cellular function (Bowen et al., 2016). Furthermore, although soybean oil contains low amounts of omega-3 it is much higher in omega-6 which have negative effects in human health when consumed in excess. For these collective reasons, the use of soybean oil in food products is not recommended.
Canola (Rapeseed) oil
Canola oil is a popular oil which is found in a wide-range of commercially available foods. Canola (Brassica napus L.) derived via the crossbreeding of the rapeseed plant which originated in Canada (Can = Canada, ola = oil). The history of rapeseed has documented that it was cultivated around 2000 B.C.E. in India and introduced to Japan and China circa 35 B.C.E. Canadian rapeseed production increased following the critical shortage of its production during WWII where it was used as a lubricant for marine engines in navel and merchant ships.
Since the creation of this oilseed crop, many variations have come into fruition with the aim of improving the seed quality. Most canola crops are genetically modified (GMO) with the aim of increasing the plants tolerance to herbicides (i.e., weed killers developed to improve crop yields) and to improve the quality of the oil[7] (Sohn et al., 2022).
Canola oil undergoes several steps in relation to the manufacturing process which include (1) cleaning the canola seeds to remove impurities such as dirt (2) pre-heating the seeds to around 35°C then flaking the seeds by roller mills to break and separate the cell wall of the seed (3) cooking the seeds with a steam-heated cooker for around 15-20 minutes at around 176–221°F (80°–105°C), (4) pressing the cooked canola seed flakes to remove around 50-60% of the oil from the flakes, (5) a process called solvent extraction which uses a chemical called hexane to obtain the rest of the oil from the 18%-20% of the remaining seed flakes, (6) the next stage is called desolventizing; a process which strips hexane from the canola meal by heating it for the third time at 203-239°F (95–115°C) through steam exposure, (7) the final stage is processing the oil which is refined via different methods such as steam distillation, exposure to phosphoric acid, and a filtration process involving acid-activated clays. If the oil is used as an ingredient in margarine, or other buttery spreads, it will additionally go through a hydrogenation process in which hydrogen molecules are added to the oil to alter its chemical structure. Due to its intensive production methods, the deodorization process may alter fatty acids into artificial trans fats. Heating methods used during the canola manufacturing as well as high-heat cooking methods negatively impact the polyunsaturated fatty acids content. Certain oils containing saturated fats such as coconut oil are more suited to high-heat cooking oils including frying as they are the least susceptible to oxidation.
In terms of composition, canola oil contains around 64% monounsaturated fats and around 7% saturated fats. It also contains around 28% polyunsaturated fatty acids. The polyunsaturated fatty acids include linoleic acid (omega-6) and alpha-linolenic acid (ALA) at a 2:1 ratio (Sohn et al., 2022). This ratio is considered favourable by some researchers in terms of a dietary oil suitable for human health. A recent systematic review and meta-analysis investigated the effects of canola oil on body weight and other body fat indexes and demonstrated that canola oil consumption led to a modest but significant reduction in body weight. No other significant effects were found on other body composition indexes (Sohn et al., 2022).
One key consideration is the conversion from ALA to DHA and EPA, which can be problematic, inefficient and complex (Burns-Whitmore et al., 2019). The biochemical conversion pathway is mediated by diet, genetics and other factors. For example, elevated intakes of the omega-6 LA competitively interfere with the endogenous conversion of alpha-linolenic acid (ALA) to EPA and DHA (Burns-Whitmore et al., 2019). The omega-3 polyunsaturated ALA however is considered beneficial to human health and is thought to play a role in lowering triglycerides which is considered to be beneficial for heart health (Sala-Vila et al., 2022). In addition, canola oil is rich in Vitamins E and K. A recent independent study found that canola oil improved lipid profile and insulin sensitivity in women with polycystic ovarian syndrome (PCOS) (Yahay et al., 2021). There is some evidence that canola oil may help support a modest decrease in body weight (Raeisi-Dehkordi et al., 2019), was found to significantly improve various cardiometabolic risk factors compared to other edible oils (Amiri et al., 2020) and significant effect of canola oil on total cholesterol (TC) and low-density lipoprotein cholesterol (LDL) compared to sunflower oil and saturated fats (Ghobadi et al., 2019). There are also experimental animal studies linking canola oil consumption to increased inflammation and oxidative stress (Mboma et al., 2018; Papazzo et al., 2011). However more research is needed on the effects of canola oil and human health, and animal studies are often poor predictors of human reactions and the findings do not necessarily translate or are replicated in human trials (Bracken, 2009).
Cottonseed oil
Cottonseed oil is a vegetable oil which is manufactured from the seeds of cotton plants. A whole cotton seed contains around 15-20% oil. Cottonseed oil contains approximately 55% omega-6 linoleic acid, 18% monounsaturated fatty acids (namely oleic acid) and 27% saturated fat. Unrefined cottonseed oil contains a substance called gossypol (a toxic crystalline compound) which is a naturally occurring toxin that provides the oil its yellow colour. Gossypol is produced by pigment glands in cotton stems, leaves, seeds, and flower buds (Gossypium spp.). Although, it is distributed throughout the cotton plant, the greatest concentration of gossypol is in the seeds (Gadelha et al., 2014). Gossypol is resistant to pests and has a protective role of the plant from insects; hence it is sometimes used as a pesticide. The extensive refining process is thought to remove the potential of gossypol toxicity which is important because gossypol is associated with various forms of poisoning including interference with the immune system, impairment of the human reproduction systems, liver damage and respiratory distress (Gadelha et al., 2014) .
In terms of uses, cotton seed is commonly used in processed, baked food products (e.g., margarine, crisps, potato chips, mayonnaise, cookies, and crackers) due to its ability to extend shelf-life. It is also used in deep frying in many fast-food restaurants as it is inexpensive and may help enhance the flavour of food products. Cottonseed oil is extensively refined and, the process subsequently removes its Vitamin E content. The oil is also subjected to destabilisation and oxidation when exposed to high heat and for that reason, may contain partially hydrogenated oils or trans fats, which raise your risk for cardiovascular disease and diabetes (Iqbal, 2014). There is mixed evidence for the use of cottonseed oil consumption in terms of potential harms or benefits (Yang et al., 2021). For example, some research suggests that cottonseed oil may increase LDL particles which may increase risk for atherosclerotic heart disease while other research report helpful health markers such as lower cholesterol and triglycerides (Davis et al., 2012; Polley et al., 2018; Prater et al., 2022), lowering inflammation (Liu et al., 2020), and the alleviation of ischemic stroke injury in experimental animal models (Liu et al., 2020). Cold-pressed, organic, cottonseed oil is considered to be beneficial for the skin due to its high concentrations of Vitamin E, fatty acids and antioxidants.
Coconut Oil
The use of coconut oil is cooking has widely grown in popularity potentially due to the increase and interest in consumers following a ketogenic diet. It has been cited in Ayurvedic medicine as containing health-related properties almost 4000 years ago. However, its use is often controversial. What is known is that extra-virgin, cold pressed, expeller-pressed, organic oil does not contain carbohydrates and is rich in healthy bioactive fats called monounsaturated fatty acids or MUFAs. In relation to its use in the ketogenic diet, ketosis is a metabolic state in which your body burns fat for fuel as opposed to carbohydrates. It is a process popular among patients with epilepsy (Sampaio, 2016), but has also appealed to mainstream followers as well as individuals with autism spectrum disorder, ADHD and type 2 diabetes (Bostock et al., 2017; Li et al., 2021; Westman et al., 2018). The ketogenic diet limits intake of carbohydrates to 20-50 grams per day and recommends that protein accounts for 20% of your daily food intake and around 70-75% should come from fat, which is where the use of coconut oil is recommended. Ketones also supress appetite by potentially altering hormone levels of ghrelin (the hunger hormone) (Stubbs et al., 2018). Furthermore, ketogenic diets are health-promoting and may act as an aid in weight-loss due to their medium-chain triglycerides (MCT) oil content. Conversely, coconut oil is fairly high in calories (e.g., it contains around 120 calories per 1 tablespoon, 14 grams) and its dietary use is recommended sparingly. More research and larger studies are required to determine its potential weight loss properties (Bueno et al., 2015; Mumme & Stonehouse, 2015).
Coconut oil is rich in MCTs which are a type of saturated fat and are metabolically absorbed differently to other types of saturated fats (Hewlings, 2020). MCTs are linked to several health benefits linked to its many bioactive compounds such as polyphenols as well as containing lauric acid which is thought to have antimicrobial and antifungal properties and may help healthy immune system functioning (Joshi et al., 2020; Nitbani et al., 2022; Wallace, 2019). Coconut oil is a source of beneficial antioxidant compounds such as flavonoids, tocopherols and polyphenols. Collectively these help protect the body and its cells from damage caused by free radicals and environmental pollutants which in turn may be protective against neurodegenerative processes and disease (Pizzino et al., 2017).
MCTs are metabolized in part in the mitochondria of the liver to produce ketone bodies, such as 3-β-hydroxybutyrate, acetoacetic acid, and acetone (Mierziak et al., 2021). These are then transported to the organs of the body such as the brain, which can use ketones for energy production (Fernando et al., 2015). Lauric acid contributes to 50% of the MCTs present in coconut oil (Hewlings, 2020) and may inhibit the growth of pathogenic bacteria and increase immune cell capabilities (Illam et al., 2021; Sheela et al., 2017; Widianingrum et al., 2019). There is conflicting evidence surrounding whether or not coconut is beneficial for heart health with mixed findings in the published literature (Neelakantan et al., 2020; Sankararaman & Sferra, 2018).
Finally, coconut oil is suitable for pan-frying and baking and is considered heat stable. Below 25°C it is sold and considered to be coconut fat (Chandran et al., 2017). Please note, it is refined coconut oil as opposed to virgin coconut oil which has a higher smoke point, e.g., 400 to 450°F. However, the refining process also decreases its distinct and natural flavour and also removes its antioxidant and polyphenol properties.
Palm oil
Palm oil is manufactured from the fleshy fruit of oil palms known as the Elaeis guineensis tree, which is native to the coastal countries of Southwest and West Africa, including Angola, Gabon, Liberia, Sierra Leone, and Nigeria (Gruca et al., 2015). Unrefined palm oil has a red-orange colour and is known as red palm oil. A similar oil palm which is native to south America and called Elaeis oleifera is not often manufactured commercially but occasionally a hybrid of both plants is used in palm oil production (Osorio-Guarín et al., 2019). Palm oil production has since expanded to Southeast Asia including both Indonesia and Malaysia, collectively these 2 countries produce over 80% of the world’s palm oil (Vijay et al., 2016). The use and sale of palm oil is controversial due to its attributed role in the deforestation of rainforests and impact on endangered species.
Palm oil contains a high saturated fat content, around 1.5 grams of PUFAs and 2 grams of Vitamins E. The refined version is commonly used during high heating applications such as frying as it has a high smoke point of 450 °F (232 °C) and known stability (Tarmizi & Ismail, 2014). Palm oil contains around 120 calories per 14 gram serving. It has around 14 grams of fat, 7 grams of saturated fat, 5 grams of monounsaturated fat, 1 gram of polyunsaturated fat and around 14% of the recommended daily amount of vitamin E. Palm oil compromises approximately 50% saturated fatty acids, 40% monounsaturated fatty acids, and 10% polyunsaturated fatty acids.
AhiFlower Oil
AhiFlower oil is plant-based source of omega-3 originating from a naturally wild plant growing in a hedgerow in the UK countryside. It has since been cultivated as a non-GMO agricultural crop produced exclusively by Natures Crops International. Each AhiFlower bloom produces up to four seeds. These seeds are freshly expeller-pressed to produce a complete and balanced omega-rich oil with a high quality and larger quantity of omegas than other seed oils in the commercial marketplace.
AhiFlower Seed Oil provides omega-3 precursors to EPA and DHA due to its rich ALA and stearidonic acid (SDA) content. Stearidonic acid is the by-product of the delta-6 desaturation of alpha-linoenic acid (ALA)[8]. It has been demonstrated scientifically to increase circulating levels of EPA and anti-inflammatory GLA levels. Recent research, although preliminary, has demonstrated a relatively rapid DHA turnover from non-marine fish sources. This has potential important clinical implications for achieving a healthy omega-6/3 balance and maintaining physical wellness. Clinical trials in humans with AhiFlower oil have demonstrated a superior-up to 4x greater EPA conversion efficiency rate in comparison to flaxseed oil. Furthermore, AhiFlower oil supports the body’s natural anti-inflammatory response. AhiFlower oil has a unique ALA and SDA content which supports its pro-EPA equivalency to about half that of standard fish oil. There is a growing demand for plant-based sources of omega nutrition, given humans cannot produce EPA and DHA in the body and rely on dietary sources. Furthermore, wild-capture fish stocks are unable to meet minimum intake recommendations for EPA and DHA for our growing planetary population of 7+billion people. AhiFlower has the ability to convert DHA more readily than flaxseed oil and about 90% as efficiently as a pure marine-based DHA source.
AhiFlower has been found to enrich critical cell membranes with a complete spectrum of omegas, converting readily and efficiently to circulating and tissue DHA.
Natures Crops argue that incorporating AhiFlower oil into the daily diet can replace other EPA/DHA sources[9] as they supply all the omegas required for optimal wellness. Finally, AhiFlower is sustainable and regeneratively grown by a dedicated group of UK farmers who follow regenerative agriculture best practices and traceability protocols.
Throughout the entire growing season, AhiFlower crops are monitored, and particular attention is paid to soil health, pollinator activity, carbon capture, and biodiversity. AhiFlower is considered to provide support for heart- and brain-health, immune system function, inflammation response and skin health[10].
Trans-Fats & the Hydrogenation Process
Trans-fats are a type of unsaturated fatty acid. There are clear differences in natural trans fats versus artificial, industrially produced, trans fats. These are known as partially hydrogenated fats which occur when refined vegetable oils are altered in their chemical structure with the main aim of prolonged shelf life. Artificial trans fats are linked to an increased risk of cardiovascular disease (Oomen et al., 2001; Sun et al., 2007). Trans-fats may also increase risk of diabetes. One large study with over 80, 000 women found a 40% increase risk of diabetes in those consuming trans fats (Hu et al., 2001). Trans fats are also linked to an increase in inflammation which is thought to be the primary cause of metabolic syndrome (Mozaffarian et al., 2004). Trans fats are thought to cause damage to the inner lining of blood vessels (the endothelium). The main source of trans fats in the human diet are via the consumption of partially hydrogenated vegetable oils found in a variety of processed foods. The World Health Organization advice is that humans should not consume more than 2 g of trans fat a day. However, in 2018, the FDA banned the use of partially hydrogenated vegetable oil in processed foods. Partially hydrogenated vegetable oils and refined oils such as soybean, cottonseed, corn and canola are among the worst culprits and can contain up to 60% trans fats contributing to 0.6 g daily of trans fats in the diet. The collective research indicates that trans-fat may lead to insulin resistance, long-term inflammation and Type 2 diabetes and there is an increased risk in those with obesity or excess weight.
Summary
Collectively, seed oils due to their high omega-6 content should be approached with caution and, arguably many of these should be avoided for human health. The most highly recommended oils in the literature are avocado oil, olive oil and coconut oil and these are considered ideal. In relation to the seed oils reviewed in this paper AhiFlower, coconut and high-oleic sunflower oil are likely the most suitable candidates for inclusion in food products.
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