Health-Promoting Benefits of Vegetable Oils

Health-Promoting Benefits of Vegetable Oils: History

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Subjects: Food Science & Technology

Contributor:

Mingke Tian

Yuchen Bai

Hongyu Tian

Xuebing Zhao

Vegetable oil is an indispensable ingredient in the human daily life diet, not only due to its sensory attributes when used as a cooking medium, but also as an supply energy to maintain body normal temperature. VOs provide essential fatty acids (EFAs) which serve as carriers for liposoluble vitamins, act as precursors for steroid hormones and prostaglandins synthesis, and play a significant role in health protection and disease prevention.

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chemical compositions
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nutritional properties
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edible oils

1. Introduction

The composition of vegetable oil is known to include not only EFAs, but also micronutrients such as phytosterols, tocopherol, carotenoid, and phenolics, etc. The functional value of VOs includes their reduction in free radicals, lowering of blood cholesterol, and prevention chronic diseases. For these effects, which result from the functional compounds in VOs, the health-promoting benefits are discussed in the following sections.

2. Antioxidant Activity

Reactive oxygen species (ROS) and free radicals (FR) are generated during metabolism in vivo as well as during exposure to adverse pathophysiological conditions [50]. ROS or FR can initiate oxidative stress, wherein the single electron seeks to pair with biological macromolecules such as lipids, proteins, and DNA, leading to damage along with lipid peroxidation. The generation of ROS contributes to many chronic diseases such as atherosclerosis, diabetes, inflammatory diseases, and cancers. Therefore, some active components, such as tocopherols, phytosterols, carotenoids, and phenolics, which have free radical scavenging capacity in VOs, may combat the cell oxidative damage and benefit human health. The 1.

Table 1. Function of vegetable oils in antioxidant activity.

Functional Components	Oil Types	Mechanisms	References
Tocols	Pomegranate seed oil Soybean oil Cress oil	Primary or chain breaking antioxidants; tocopherols can provide electrons to FR to make them become inactive compounds with the exchange of becoming tocopherol FR, which is easy excrete in feces and urine after metabolism.	[9,52]
Phytosterols	Rice bran oil Corn oil	Possible primary or chain breaking antioxidant.	[52]
Phenolics	Coconut oil Torreya grandis seed oil	Primary or chain breaking antioxidants. Secondary or preventive antioxidants act as chelators of metal ions. Stabilize and prevent decomposition of hydroperoxides. Phenolic compounds can prevent the generation of FR in the body and block the oxidation reaction of PUFAs or LDLs induced by FR.	[52]
Carotenoids	Tomato seed oil Sea buckthorn seed oil	Secondary or preventive antioxidants act as singlet oxygen quenchers. Primary or chain breaking antioxidants. Carotenoids are able to donate an electron and neutralize FR, resulting in the suppression of excess FR production to inhibit the deterioration of internal redox balance and terminate some chain reactions.	[52]
Fatty acids	Flaxseed oil	n-3 PUFAs can reduce mitochondrial dysfunction and endothelial cell apoptosis associated with oxidative stress by increasing the activity of endogenous antioxidant enzymes.	[53]

The antioxidant mechanism of tocopherols is to provide electrons to FR making them inactive compounds through which they can be exchanged to tocopherol FR. Tocopherol radicals are stable and can form dimers, trimers, or be converted to tocopherol quinine, which is metabolized and excreted [10]. Recent studies have shown that the high levels of γ-tocopherol in pomegranate seed oil contribute to its powerful antioxidant capacity [54]. Cress oil is a relatively stable oil due to the presence of a high concentration of antioxidants such as tocopherols and carotenoids [55]. Soybean oil also exhibits excellent antioxidant properties, which are associated with tocopherols, suggesting that it can effectively quench FR, and reduce lipid peroxidation [56].

Phytosterols have antioxidant potential due to their ability to inhibit oxidative degradation of lipids and their strong scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals and hydroxyl radicals. Rice bran oil, which is rich in unsaturated linoleic and oleic acids as well as bioactive compounds such as γ-oryzanol, phytosterols, tocopherols, and tocotrienols, exhibited significant antioxidant activity in the inhibition of cholesterol oxidation. The higher levels of stigmasterol and β-sitosterol in corn oil give it a higher scavenging capacity for DPPH FR than grape seed and coconut oils, thus exhibiting its antioxidant activity [57].

Carotenoids are essential antioxidants that are able to donate an electron and neutralize FR, resulting in suppression of the excess FR production, which inhibits the deterioration of internal redox balance and terminates some chain reactions [58]. Carotenoids have been well-characterized for their antioxidant activity in vitro, and recent data have also shown their ability to specifically limit PUFA peroxidation in lipid membranes [59]. Current research has identified a number of types of seed oils from new sources that contain high levels of antioxidant compounds and have the potential to be incorporated into foods as functional edible oils or as natural antioxidants. Tomato seed oil has been shown to contain high levels of carotenoids, particularly β-carotene, which has high antioxidant activity due to its ability to burst singlet oxygen and trap peroxyl radicals [60]. In addition, sea buckthorn seed oil is high in carotenoids and is a potent antioxidant within in vitro model systems [61].

The mechanism of phenolic compounds is to prevent the generation of FR in the body and block the oxidation reaction of PUFAs or low-density lipoproteins (LDLs) induced by FR. Coconut oil, especially virgin coconut oil, has the highest total phenolic content among the 39 VOs, as well as has high levels of polyphenols, tocopherols, phytosterols, and monoglycerides, resulting in excellent free radical scavenging activity and high antioxidant capacity [62]. Additionally, a study on Torreya grandis seed oil showed that its samples exhibited concentration-dependent antioxidant activity through a DPPH free radical scavenging test and a β-carotene bleaching test to assess lipid peroxidation inhibitory activity, leading to the conclusion that the high total phenolic compound content may be attributed to its potent antioxidant activity [63].

Furthermore, EFAs, especially ALA, are crucial to antioxidant capacity. The antioxidant, antihyperglycemic, and antihyperlipidemic activity of flaxseed oil can be attributed to the presence of linolenic acid and its metabolites EPA and DHA [64]. After ingestion of LA, the activity of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) is enhanced, and the generation of free radical metabolite malondialdehyde (MDA) decreases, thus achieving free radical scavenging, reduced cell damage, and improved tissue and organ function. Similarly, the activity of GSH-Px and SOD in the liver and kidney of mice was increased by grape seed oil, and the MDA content in all organs was decreased. Millan-Linares et al. reported that due to the high content of LA (58–78%), the unsaponifiable fraction isolated from grape seed oil attenuated oxidative and inflammatory responses in lipopolysaccharide (LPS)-treated human primary monocytes by suppressing intracellular production of ROS and nitrite levels as a consequence of reduced nitric oxide synthase-2 (Nos2) gene expression [65].

3. Prevention of Cardiovascular Disease (CVD)

CVD is the number one leading cause of death worldwide, causing an estimated 17.9 million deaths each year [66]. The progress of inflammation in the blood vessels and endothelial dysfunction causes an atherosclerotic lesion in the arteries, which further induces stroke and myocardial dyslipidemia, as is indicated by elevated concentrations of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and triglyceride (TG), as well as low concentrations of high-density lipoprotein cholesterol (HDL-C) which continues to be a major CVD risk factor [67]. Additionally, age, smoking, detrimental diet, lack of exercise, psychological stress, diabetes, and obesity increase this burden. The studies summarized in Table 2 show the consumption of representative nutritionally rich VOs potentially reduces the risk of CVD, and attributed this to the content of MUFA, PUFA, and phytosterols. The substitution of SFAs, such as animal fats and dairy products, with VOs that are high in MUFA and PUFA is emphasized as regulating the blood lipid profile.

Table 2. Function of vegetable oils in preventing cardiovascular diseases.

Functional Components	Oil types	Mechanisms	References
MUFA	Almond oil Olive oil	Oleic acid can decrease plasma triacylglycerol and cholesterol concentrations.	[68]
PUFA	Flaxseed oil Pomegranate seed oil	LA helps to break down cholesterol by promoting cholesterol 7α-hydroxylase (CYP7) activity. LA enhances transcription of the liver X receptor (LXRα) gene via peroxisome proliferator-activated receptors (PPARs). In turn, LXRα upregulates the expression of the CYP7 gene; EPA and DHA protect the blood vessels and heart by regulating membrane phospholipids, improving cardiac mitochondrial function and energy production, and lowering triglyceride concentrations.	[69,70]
Phytosterols	Rice bran oil Corn oil Rapeseed oil	Inhibits the absorption of intestinal cholesterol.	[10]

MUFA helps to prevent the oxidation of LDL-C. LDL particles which undergo oxidation in the arterial wall result in the atherosclerotic process. The Mediterranean diet which is rich in MUFA has been proven to decrease cardiovascular morbidity and mortality [71]. Oleic acid (OA) can decrease plasma triacylglycerol and cholesterol concentrations without affecting plasma HDL-C levels in healthy normolipidemic subjects [68]. A recent meta-analysis focusing on the effects of different dietary sources of MUFAs on CVD provided evidence that olive oil was associated with a significant risk reduction in all-cause mortality, cardiovascular events, and stroke [72]. Almond oil dominated by OA has been proven to improve endothelial function effectively. If endothelial function is damaged, it will lead to atherosclerotic vascular disease. Therefore, almond oil is beneficial to cardiovascular system [73].

PUFA, especially linoleic acid (LA) and linolenic acid, in vegetable oil helps to regulate the blood plasma TG levels in patients with dyslipidemia, lower the blood pressure, and protect against coronary heart disease [74]. Marangoni et al. reported that epidemiological studies have shown that adequate intake of LA reduces plasma LDL-C and illustrated that dietary intervention studies have shown that replacing 5% of dietary SFA energy with ω-6 PUFAs reduces LDL-C by up to 10%, the risk of coronary events by 13%, and the risk of coronary death by 26% [75]. Several studies have shown that PUFA protects the blood vessels and heart by regulating membrane phospholipids, thereby improving cardiac mitochondrial function and energy production and reducing TG concentrations [76]. Therefore, VOs rich in PUFA are widely recommended as a way to reduce the risk of CVD. Han et al. reported that flaxseed oil is rich in ω-3 PUFAs, and that ALA (39.00–60.42% of the major fatty acid) suppresses the biosynthetic pathway of cholesterol and TG by regulating the expression of sterol regulatory element-binding proteins 3-hydroxy-3-methylglutaryl coenzyme-A (HMG-CoA) reductase, sterol regulatory element-binding proteins 1c (SREBP-1c), and acetyl-CoA carboxylase, thus illustrating that partial replacement of lard with flaxseed oil can significantly alleviate atherosclerosis symptoms, improve oxidative stress, reduce lipid and inflammatory abnormalities, and promote cardiovascular health [77,78]. Several studies have also shown that perilla seed oil, sea buckthorn seed oil, walnut oil, and other polyenoic VOs have hypolipidemic health effects and can prevent and treat CVD due to the high content of LA and linolenic acid which reduce the plasma concentrations of TC, LDL-C, very low density lipoprotein cholesterol (VLDL), apolipoprotein B, and apolipoprotein A-1 [79]. Pomegranate seed oil is rich in PUFAs, and a recent study using a hamster model has shown that it is effective in lowering plasma and liver cholesterol, as well as in increasing HDL/LDL ratios when partially replacing saturated fat in a high-fat diet [80].

Phytosterols are well known for their cholesterol-lowering ability. An average daily dose of 2 g phytosterols lowers plasma LDL-C by approximately 0.31–0.34 mmol/L or 8–10% within 3–4 weeks [81]. Their ability to lower LDL-C concentrations through reduced intestinal absorption has been well documented [67]. Some bioactive accompaniments of grape seed oil, such as phytosterols and polyphenols, have also been shown to prevent and improve hypertension [82]. In addition, the high phenolics, phytosterols, and tocopherols in cold-pressed rapeseed oil help to reduce the absorption of dietary cholesterol and decrease the risk of hyperlipidemia and CVD. Thus, cold-pressed rapeseed oil can be used as a supplement to offer a cholesterol-lowering effect [35]. Yang and coworkers estimated phytosterol intake in the Chinese diet, and the results show that the phytosterol contents of rice bran oil, corn oil, and rapeseed oil are higher than those of other VOs and play a vital role in the reduction in cholesterol in blood, as well as decreasing cardiovascular morbidity [28]. Additionally, phytosterols which are present in high concentrations in pomegranate seed oil inhibit the absorption of intestinal cholesterol. Therefore, they play a natural preventive role in CVD. In 2011, the European Food Safety Authority (EFSA) approved a claim that extra virgin olive oil (EVOO) polyphenols protect blood lipids against oxidative stress at a minimal dose of 5 mg/kg/day [83].

4. Anti-Inflammatory

Inflammation is one of the primary factors associated with the causation and progression of several lifestyle disorders, it is associated with many diseases, including obesity, type 2 diabetes mellitus (T2DM), cancer, anaphylaxis, arthritis, and non-alcoholic fatty liver disease (NAFLD), etc. Additionally, inflammation can cause genetic defects, disrupt immune regulation, and damage the body tissues [84]. Diet and inflammatory response are recognized as strictly related, and PUFAs present in vegetable oil, particularly ω-3 polyenoic acids, can achieve anti-inflammatory effects by competing with AA for metabolism and participating in the regression of inflammation and tissue repair, thus affecting the nuclear factor-κB (NF-κB) pathway and altering the lipid raft pathway, among other mechanisms. LA can reduce the levels of inflammation-related factors such as interleukin-1β (IL-1β), tumor necrosis factor alpha (TNF-α), and nitric oxide (NO), and has a significant ameliorating effect on both acute and chronic inflammation [79]; ALA and GLA possess anti-inflammatory and anti-allergic properties to improve the immune system, as well as serve as a precursor of the prostaglandin and tissue hormones. The functions of some VOs as anti-inflammatories and their mechanisms are summarized in Table 3.

Table 3. Anti-inflammatory function of vegetable oils.

Functional Components	Oil Types	Mechanisms	References
USFA	Flaxseed oil Perilla seed oil Almond oil	ALA exerts an anti-inflammatory effect by upregulating the expression of Peroxisome proliferator-activated receptor γ to inhibit the transcription of pro-inflammatory cytokines. EPA and DHA reduce the production of AA-derived eicosanoids by competing with AA for incorporation into cell membrane phospholipids, reduce AA release from the membrane, inhibit the action of the enzymes COX-2 and 5-lipoxygenase (5-LOX) on AA, or compete with AA for metabolism by COX and LOX enzymes.	[69,85]
Phytosterols	Rice bran oil	Phytosterols can suppress the transcription of inflammatory genes in macrophages.	[86]

A large body of evidence has demonstrated the efficacy of ω-3 long-chain polyunsaturated fatty acids (ω-3 LCPUFA) in NAFLD conditions, due to their anti-inflammatory, immunomodulatory, and anti-viral properties. Therefore, intervention with ω-3 LCPUFA, an effective pharmaconutrient, along with the standard treatment for COVID-19 may be useful in the management of NAFLD spectrum in COVID-19 patients with pre-existing NAFLD conditions by resolving the inflammatory cytokine storm, thereby attenuating its progression [87]. Arthritis is a joint disorder resulting in joint pain, it is usually caused by inflammatory substances and joint wear. Studies have found that flaxseed oil was effective in the treatment of knee osteoarthritis, especially in the aspects of ameliorating the severe symptoms and functional status, due of its anti-inflammatory ability [88]. Atefeh Akrami et al. observed a beneficial effect of flaxseed oil consumption on reducing the inflammatory state (including serum IL-6 concentrations) in patients with metabolic syndrome, a chronic disease with an inflammatory and hypercoagulable state [89]. The study showed that compared to olive oil and safflower oil, perilla seed oil in particular has a better protective effect against inflammation of the colon caused by a high-fat diet due to its richness in ω-3 PUFAs, especially ALA, the precursor of EPA and DHA. The mechanism of this feature is that ALA exerts an anti-inflammatory effect by upregulating the expression of peroxisome proliferator-activated receptor γ to inhibit the transcription of pro-inflammatory cytokines [85]. Almond oil had significant inhibitory and analgesic effects on an early ear swelling inflammation model, significantly reduced the number of glacial acetic acid-induced torsion occurrences, and increased the pain threshold in hot plate method mice with a more pronounced quantitative effect relationship. Evening primrose oil is extremely high in LA and GLA, which are precursors to the anti-inflammatory eicosanoids, and thus may contribute to the normal functioning of human tissues with anti-inflammatory and anti-proliferative properties [90].

The presence of phenolic compounds, phytosterols, and tocopherols together in VOs may prevent the development of chronic diseases by their anti-inflammatory, antioxidant, neuroprotective, and immunomodulatory activities. Micallef et al. showed that a diet rich in ω-3 polyenoic acids and phytosterols reduced systemic inflammation in hyperlipidemic individuals; in addition, the combination of ω-3 polyenoic acids and phytosterols may result in anti-inflammatory effects through the conversion of ALA (C18:3n-3) to DHA (C22:6n-3), thereby possessing cardioprotective effects [79]. For example, rice bran oil contains tocopherols, tocotrienols, and γ- oryzanol, and the results of in vivo and in vitro experiments highlight its ability to ameliorate chronic low-grade inflammation caused by obesity through mediating the expression of inflammation-related factors and macrophage polarization [91]. Grape seed oil may also be considered a suitable candidate for the treatment or prevention of ulcerative colitis because of its anti-inflammatory activity due to the presence of many bioactive components such as phytosterols, vitamin E, and polyphenols [92].

5. Anti-Obesity

Obesity refers to a certain degree of obvious overweight or a too thick fat layer, especially when caused by TG accumulation [93]. Fat overload in the adipose tissue leads to adipocyte dysfunction, which may stimulate the development of various endocrine and metabolic disorders by affecting glucolipid metabolism and increasing the inflammatory response, and is closely associated with chronic diseases, which include insulin resistance, T2DM, hypertension, dyslipidemia, and CVD [94]. The obesity epidemic is one of the most serious health problems worldwide and obesity is becoming increasingly prevalent in younger people in many countries. VOs with medium and long chain fatty acids are effective in controlling body mass, lowering TG, and improving apolipoprotein metabolism. An understanding of fats and fatty acids in needed to validate the consumption of VOs containing the EFAs in moderation to aid in the control of weight, and better health. High leptin levels and low adiponectin levels are characteristic of obesity. Adiponectin promotes β-oxidation by mediating the phosphorylation of adenosine 5‘-monophosphate (5′-AMP) activated protein kinase and activating peroxisome proliferation-activated receptor alpha. Thomas et al. showed that three oils, perilla seed oil, safflower oil and olive oil, may improve high-fat diet-induced obesity by reducing lipogenesis and increasing β-oxidation, and these results highlight the importance of replacing saturated fats with unsaturated fats, particularly with PUFA-rich perilla seed oil, which can be seen as a healthy dietary pattern [94]. Akrami et al. clearly showed that consumption of flaxseed oil rich in PUFAs significantly reduced body weight and lowered waist circumference in patients with anti-obesity effects due to a positive linear relationship between eicosanoids in ω-6 PUFA and body mass index (BMI) and waist circumference. The ω-3 PUFA interacted with the regulation of signals related to fat accumulation or energy metabolism [95].

6. Anti-Cancer

Cancer is a generic term for a large group of diseases that can affect any part of the body. One defining feature of cancer is the rapid creation of abnormal cells that grow beyond their usual boundaries, which can then invade adjoining parts of the body and spread to other organs. According to WHO statistics in 2020, the most common cancers in the world are breast, lung, colon, rectal, and prostate cancers [96].

Phytosterols inhibit cancer cell growth and reduce the metastatic ability of cancer cells through cell cycle arrest and the induction of apoptosis, and have been shown to be effective in breast, colon, leukemia, and prostate cancer metastasis. A daily consumption of phytosterol-rich foods can reduce the risk of cancer by 20% [97]. It is also proposed that the phytosterols exert effects on membrane structure, integrity and fluidity, membrane-bound enzymes, signal transduction pathways, apoptosis, and immune function of host tissues. Yu et al. concluded that rice bran oil containing phytosterols and γ-oryzanol may play a vital role in suppressing local inflammation, inhibiting the cancer cell cycle, promoting apoptosis, and enhancing chemo preventive effects, and are considered to be promising adjuvant therapeutic agents for cancer prevention and treatment [98].

In addition, LA helps to inhibit the growth of human breast cancer, colon cancer, skin cancer, stomach cancer, and leukemia [35]. Many studies have shown that treatment of B16-BL6 mouse melanoma and MCF-7 breast cancer cells with LA-rich linseed oil induces apoptosis and disrupts their mitochondrial function in a dose-dependent manner, thereby inhibiting the growth of cancer cell lines in particular. Other studies have shown that flaxseed oil can inhibit the formation and growth of various tumors and cancers, such as colon, breast and skin cancers, and can also enhance the effectiveness of anti-cancer drugs, suggesting further potential for flaxseed oil in anti-cancer therapy [99]. Although many of the substances in flaxseed oil show anti-tumor activity, it is still not possible to clearly elucidate the mechanisms of these components or how they show the ability to reduce the development of cancer [66]. GLA leads to increased levels of polyomavirus enhancer activator 3 protein (Pea3), a transcriptional repressor of human epidermal growth factor receptor 2 (HER-2/neu) in cells, and reduces HE-2/neu promoter activity, thereby reducing the likelihood of breast cancer; it also inhibits the expression of the nm-23 metastasis suppressor gene in cancer cells, thereby inhibiting angiogenesis and cancer cell migration, and achieving the effect of inhibiting the occurrence of metastasis. Thus, evening primrose oil has proven anti-cancer therapeutic functions due to the above mechanisms [90]. Furthermore, perilla seed oil inhibits the development of colon tumors with methyl nitrosourea mainly because the presence of ALA modifies the sensitization of colon cell membranes to carcinogens.

Similar to phytosterols, tocopherols were found to induce programmed cell apoptosis in human colon cancer cell while inhibiting growth of prostate cancer cell [100]. Camellia oil, olive oil, and cottonseed oil blocked intercellular communication and prevented lung metastasis of patients’ melanoma cells [101].

Phenolic compounds found in foods significantly affect their stability, sensory, and nutritional characteristics, and may prevent their spoilage through quenching radical reactions responsible for lipid oxidation [102]. It has also been proven that dietary inclusion of phenolic compounds provides many benefits due to their anti-inflammatory and anti-carcinogenic effects, especially in breast cancer therapy [103]. Canolol is a unique compound in rapeseed oil which has been shown to reduce apoptosis in human cancer SW480 cells [35]. In addition, some studies have shown that the high levels of ellagitannins in pomegranate seed oil promote the repair of biomolecules and cells, and the high levels of lipid peroxidation in punicic acid inhibit the proliferation of cancer cells by affecting the protein kinase C (PKC) pathway, thus showing anti-cancer activity against various forms of cancer, such as breast, prostate, and colorectal cancers [104,105].

Currently, squalene is primarily obtained from deep-sea shark liver; however, due to the decreased availability of shark, more attention has been paid to plant sources, such as soybean oils and olive oils, to obtain squalene instead. Olive oil contains 0.2–0.7% squalene, which can regulate the activation of carcinogens, and effectively inhibit the occurrence of colon, lung, and skin tumors induced by rodents [106].

7. Diabetes Treatment

Diabetes mellitus refers to a type of metabolic disease with the characteristics of high levels of blood glucose [66]. In diabetes, elevated blood glucose levels increase the risk of other complications such as retinopathy, nephropathy, and neuropathy. Clinical evidence has shown that these complications can be controlled well through many dietary therapies. Significant evidence from epidemiological investigations has shown that dietary polyphenols might manage and prevent T2DM. Polyphenols have been reported to show anti-diabetic effects in T2DM patients through increasing glucose metabolism, improving vascular function, and reducing insulin resistance and glycated hemoglobin level. EVOO has been reported to protect against cardiometabolic diseases including CVD, T2DM, and obesity because it contains at least 30 phenolic compounds including simple phenols (tyrosol and hydroxytyrosol), secoroids, and lignans [107]. Daily consumption of polyphenol-rich EVOO might improve metabolic control and the profile of circulating inflammatory adipokines in overweight T2DM patients [108]. In addition, studies have indicated that flaxseed oil plays an important role in the treatment of diabetes by modulating insulin sensitivity in phospholipid membranes, modulating the gut microbiota, or reducing inflammation in the body. Coconut oil has a high total phenolic content and has shown anti-diabetic effect in animal models of type 2 diabetes, thereby ameliorating the adverse effects of diabetes on the liver and kidneys [109].

The unsaturated fatty acids in VOs also have an effect on diabetes. Intake of white sesame oil can reduce blood glucose levels, lower oxidative stress, and improve biomarkers of liver and kidney function in patients with T2DM, possibly due to the bioactive components in sesame oil, including MUFA, tocopherols, and phytosterols [110]. Punicic acid (PA) is a PUFA (18:3n-5) belonging to the conjugated linolenic acid isomer, it is particularly abundant in pomegranate seed oil, accounting for about 60.62% to 81.40%. PA exerts its anti-diabetic effect through various mechanisms, such as reduction in inflammatory cytokines, modulation of glucose homeostasis, and its antioxidant properties [111].

8. Kidney and Liver Protection

The liver functions in metabolism, synthesis, detoxification, and secretion. The main functions of the kidney are filtration, renal tubular reabsorption, and endocrine. Due to the anti-inflammatory capacity of ALA in flaxseed oil, flaxseed oil presents hepatoprotective activity by inhibiting inflammatory signaling pathways. Wang et al. found that flaxseed oil decreases the expression of IL-6, TNF-α, and cyclooxygenase-2 (COX-2), leading to the alleviation of lipopolysaccharide-induced liver injury [112]. Kheira et al. highlighted that flaxseed oil improves cisplatin-induced kidney injury through its capability to replace the PUFAs that have been attacked by oxygen FR in the brush-border membrane (BBM) with ω-3 PUFA, which increases the integrity of BBM [113].

Furthermore, Omar et al. proved that the administration of flaxseed oil protected against the observed biochemical and histopathological alterations induced by thioacetamide exposure [114]. Therefore, flaxseed oil may rely on its antioxidant effects to protect against thioacetamide-induced renal injury. In addition, sesame oil contains lignans and other acylglycerols which reduce the accumulation of liver fat, inhibit matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) by regulating the expression of tissue inhibitor matrix metalloproteinase 1 (TIMP-1), and thus reduce liver damage. Conversely, the approval for this treatment of non-alcoholic steatohepatitis (NASH) has not yet been granted by the US Food and Drug Administration [115]. Only traces of flavonolignans (500 μg/mL) were found in milk thistle seed oil, but its antioxidant, cytoprotective, and hepatoprotective activities have also been reported in vivo and in vitro [116].

9. Other Health Benefits

In addition to the previously mentioned health benefits, VOs contain a wide range of bio-active ingredients, such as lignans in flaxseed oil, nervonic acid in sour cherry seed oil, resveratrol in olive oil, lycopene in tomato seed oil, and DHA (C22:6) in grape seed oil. These special components make significant contributions to their health benefits.

Alzheimer’s disease (AD) is a chronic neurodegenerative disorder. Recently, the supplement of grape seed oil containing DHA (C22:6) to AD rats as medicinal co-treatment or post-treatment caused an obvious augmentation in spatial memory performance and acetylcholine levels [117]. Several epidemiological studies showed a negative correlation between the risk of AD and the intake of DHA. Aside from ALA, flaxseed oil is rich in dietary fibers and lignans that act as anti-oxidants and phytoestrogens, which can alleviate the intensity of symptoms associated with menopause and mental fatigue, as well as benefit autoimmune and neurological disorders [118]. Nervonic acid (C24:1, ω-9), a fatty acid found in high levels in cherry seed oil, is a precursor of neuronal cell membrane glycolipids with a key role in the modulation of ion channels and membrane receptors, and thus acts as a special supplement to promote the regeneration and repair of damaged nerve cells [119]. Lycopene is an acrylic tetraterpenic hydrocarbon with 13 carbon-carbon double bonds, 11 of which are conjugated, which presents potent antioxidant effects. It was reported that tomato seed oil, which is rich in lycopene, effectively inhibited oxidative deterioration, modulated glutathione level, and revived dopamine in the striatum, thus alleviating abnormal behavior of the neurological system [120]. The pharmaceutical functions of polyphenols, resveratrol, and non-flavonoid phenolic compounds was studied in EVOO. Intake of EVOO can effectively prevent crucial neurodegenerative conditions (aging and alcohol-related brain disorders) and neuromuscular disorders [121]. The beneficial effects of epigallocatechin gallate (EGCG), epicatechin, resveratrol, and quercetin supplements were reported in clinical trials; as an example, quercetin supplements are now commercially available in Europe and the U.S. with many health-promotion functions [32,122].

Three important factors for the nutritional evaluation of edible oils were introduced by the World Health Organization (WHO): presence of antioxidants; ratio of SFAs, MUFAs, PUFAs, and EFAs content. They suggest a ratio of 1:1.5:1 for SFAs: MUFAs: PUFAs, and a ratio of 0.8–1.0 for total polyunsaturated fatty acid (TPUFA) to total saturated fatty acid (TSFA) [12]. FAs’ ratios to several representative VOs were calculated and are summarized in Table 4. The recommended ratio of SFA: MFA: PUFA is reported for rice bran oil (1:1.8:1.4), custard-apple seed oil (1:2.2:1.1), pumpkin seed oil (1:1.0:1.9), cress oil (1:2.2:2.7), sesame oil (1:2.5:2.4), and corn oil (1:2.0:3.0). Jackfruit seed oil (0.95), olive oil (0.89), custard-apple seed oil (1.08), camellia oil (0.59), avocado seed oil (1.17) and rice bran oil (1.38) show ratios of TPUFA/TSFA closer to the WHO recommended values, while the ratios of pomegranate seed oil (16.42) and evening primrose oil (10.30) were much higher than the recommended values.

Table 4. Proportion of fatty acids in vegetable oils.

FA	SFA	MUFA	PUFA	SFA: MUFA: PUFA	TPUFA/TSFA
Soybean oil	16.18	23.88	60.98	1:1.5:3.8	3.77
Rapeseed oil	7.52	72.77	29.36	1:9.7:3.9	3.90
Palm oil	44.15	46.30	9.38	4.7:4.9:1	0.21
Peanut oil	10.70	71.10	18.20	1:6.6:1.7	1.70
Sunflower oil	11.54	28.30	67.75	1:2.5:5.9	5.87
Cottonseed oil	7.11	14.43	40.23	1:2.0:5.7	5.66
Corn oil	16.60	33.67	49.74	1:2.0:3.0	3.00
Camellia oil	17.26	72.50	10.10	1.7:7.2:1	0.59
Coconut oil	92.10	6.20	1.60	57.6:3.9:1	0.02
Olive oil	20.19	76.62	18.00	1.1:4.3:1	0.89
Flaxseed oil	12.90	23.00	76.94	1:1.8:6.0	5.96
Jackfruit seed oil	49.13	4.15	46.72	11.8:1:11.3	0.95
Papaya seed oil	19.92	76.10	3.96	5.0:19.2:1	0.20
Avocado seed oil	11.74	73.71	13.78	1:6.3:1.2	1.17
Pomegranate seed oil	5.35	6.79	87.87	1:1.3:16.4	16.42
Cheery oil	12.80	39.60	46.30	1:3.1:3.6	3.62
Sweet cherry seed oil	12.20	39.49	44.32	1:3.2:3.6	3.63
Sour cherry seed oil	7.46	38.49	54.05	1:5.2:7.2	7.25
Custard-apple seed oil	23.04	51.04	24.96	1:2.2:1.1	1.08
Cress oil	16.90	37.30	45.80	1:2.2:2.7	2.71
Pumpkin seed oil	25.20	25.54	48.14	1:1.0:1.9	1.91
Sesame oil	16.90	42.00	41.20	1:2.5:2.41	2.44
Rice bran oil	23.63	43.71	32.66	1:1.8:1.4	1.38
Almond oil	8.35	77.07	22.59	1:9.2:2.7	2.71
Evening Primrose oil	8.10	9.40	83.40	1:1.2:10.3	10.30
Perilla seed oil	8.22	12.89	76.25	1:1.6:9.3	9.28
Milk thistle seed oil	15.02	35.94	48.81	1:2.4:3.2	3.25
Tomato seed oil	24.48	21.79	53.70	1.1:1:2.5	2.19

The abovementioned health benefits of VOs are relevant to all aspects of people’s lives, and the mechanisms of nutritional ingredients need to be further explored. As for their physiological activity, studies combining lipidomics, proteomics, metabolomics, and nutrigenomics may provide further insights into the mechanisms of the health benefits induced by VOs.

This entry is adapted from the peer-reviewed paper 10.3390/molecules28176393

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