Avocado fruit have long been considered amongst the most important fruits for cardio-vascular health, and for delaying the aging process. Most of the nutritional benefits are derived from the fat content in the pulp and can be extracted into oil. Avocado oil is particularly rich in the omega-9 unsaturated fatty acid, oleic acid, whose properties in reducing serum cholesterol levels, decreasing blood pressure and preventing the hardening of arteries are very well documented. It is also a rich source of omega-3 and omega-6 polyunsaturated essential fatty acids, which also reduce LDL-cholesterol, have anti-inflammatory properties and are important for the function of the central nervous system. The unrefined oil, such as Xbrain’s virgin avocado oil, also contains all the anti-oxidant phytochemicals, such as lutein and xanthophylls found in the fruit, which protect the body from free radicals, and phytosterols, which reduce serum cholesterol levels. Virgin avocado oil is also a good source of glutathione, a powerful anti-oxidant, and of vitamin E.
Avocado Oil is a Rich Source of the Monousaturated Omega-9 Oleic Acid
Oleic acid forms up to 70% of avocado oil. Oleic acid is a gamma-9 monounsaturated fatty acid, it has only one double carbon bond, in the 9th position from its end. It protecta against heart disease by lowering the levels of LDL cholesterol, lowering blood pressure, and by maintaining blood vessel flexibility. Oleic acid might also play a role in maintaining a healthy weight by reducing the level of appetite stimulating hormones, decreasing lipid storage in the liver and enhancing beta-oxidation of lipids to produce energy. It prevents insulin resistance in tissues and protects against development of the metabolic syndrome. It is thought that the health enhancing properties of the Mediterranean diet are due to its high oleic acid content.
Many of oleic acid’s cardiac health benefits can be ascribed to its effect on serum cholesterol levels, namely the reduction of low density lipoprotein LDL in the blood. Cholesterol has very low solubility in the water, therefore it is transported in the blood bound to lipoprotein particles, which have water soluble (hydrophillic) entities on the outside of the particle, and lipid soluble (hydrophobic) entities on the inside. The lipoprotein particles can be classified according to their density, LDL particles have a higher lipid to protein ratio and are less dense than HDL particles. Apart from transporting cholesterol, lipoprotein particles also contain apolipoproteins which are recognised by specific receptors on cells. The apolipoproteins in LDL guide the cholesterol carrying particles to their target tissues. Once the cholesterol has been transported to the cells where it is needed, the receptors in the cell membrane recognise and bind the apolipoproteins. The cell engulfs the LDL-cholesterol particle through endocytosis. The cholesterol ester is then hydrolysed inside the cell by the enzyme lysosomal acid lipase, and can be used by the cell.
High density lipoprotein (HDL), which have a high proportion of protein to lipid, on the other hand, transport cholesterol to tissues where it is used in the synthesis of various hormones, or to the liver, where excess cholesterol is targetted for excretion. A relatively high level of HDL in the blood is considered to be a good predictor of cardio-vascular health.
The problem with LDL cholesterol arises when more cholesterol is synthesised than can be used by cells. Since there are more LDL particles than can be bound by cell receptors, and internalised by endocytosis. This causes the level of serum LDL to rise. The LDL-cholesterol particles are oxidised, which causes them to be taken up by macrophages, which grow in size and become the so called foam cells. these cells often become trapped on the walls of arteries, where they trap more LDL and lipid molecules and cells and start forming plaques, leading to the thickening of arteries, and atherosclerosis. Eventually this leads to decreased blood flow to the heart, and the danger that blood clots can be trapped in the arteries.
In addition, oleic acid can itself become incorporated into LDL, and it has been shown that oleate containing LDL are resistant to oxidation. Since the oxidation in LDL is the first step in arterial plaque formation and atherosclerosis, oleic acid plays a very important role in maintaining cardio-vascular health.
Oleic acid from avocado oil also plays a role in keeping the walls blood vessels flexible and in reducing blood pressure. Blood pressure is regulated through adrenoreceptors, when hormone ligands such as epinephrine bind alpha-receptors they cause vasoconstriction, while binding to beta receptors causes vasodilation and a lower blood pressure. adrenoreceptrors are G protein-coupled receptors. When the receptor, which spans the plasma membrane is bound by the ligand, it activates the enzyme adenylyl cyclase, which is docked on the cytoplasm side of the plasma membrane. The enzyme then converts cytoplasmic ATP into cyclic AMP (cAMP). cAMP is a second messenger, that transduces the signals of the hormones, and causes the smooth muscle of the blood vessel to relax, resulting in vasodilation.
Oleic acid, along with other fatty acids, becomes incorporated into the phospholipid plasma membrane, when oleic acid levels are high, the biochemical properties of the plasma membrane of endothelial cells is altered. This affects the ability of G-couple receptors to dock in the membrane, and enhances the ability of the cells to react to the vasodilating signals of the hormones.
Latest research indicates that oleic acid might also play a role in appetite control. This might explain why avocado fruit, despite their high fat content, have been found to support weight loss as part of a balanced diet. The mechanism of action appears to be through the Peroxisome proliferator-activated receptor alpha (PPAR-alpha) nuclear receptor, which is a major regulator of lipid metabolism in the liver and an appetite regulator.
Oleic acid is a precursor of oleoylethanolamide (OEA), a naturally occurring lipid that regulates feeding behaviour. OEA is an agonist of PPAR-alpha, activating it to stimulate lipid breakdown through lipolysis. OEA has been shown to decrease the levels of ghrelin and neuropeptide YY, the hunger hormones, and hence reducing appetite and food intake. Acting through PPAR-alpha, it induces the expression of genes necessary for beta-oxidation, the process which burns lipids for energy in mitochondria. It therefore reduces liver fat content, and triglycerides in the circulation. It therefore appears that increased oleic acid consumption, leads to higher levels of OEA, which in turn suppresses appetite, and increases lipid breakdown, by activating the PPAR-alpha receptor.
The Health Benefits of Essential Polyunsaturated Fatty Acids in Avocado Oil
XBrain’s Organic virgin avocado oil is also a rich source of the polyunsaturated omega-3 and omega-6 fatty acids, alpha-linoleic acid (ALA) and linoleic acid (LA). These are essential fatty acids, since they cannot be synthesised by our bodies and must be obtained from the diet. Alpha-linoleic acid, however, can be converted in the body into longer chain polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA), and docosahexaenoic acid (HDA), which play a very significant role in protecting against cardio-vascular disease.
Both omega-3 and omega-6 fatty acids are precursors to physiologically active molecules such as eicosanoids, which regulate the inflammatory response, and are active in the central nervous system, and endocannabinoids, which affect mood and behaviour. Omega-3 fatty acids have been shown by many scientific studies to have significant anti-inflammatory activities. Inflammation is part of the body’s defence against injury and infectious micro-organisms. However, it has to be carefully controlled, if allowed to proceed unchecked it results in tissue injury. In fact many of the modern diseases prevalent in industrialised countries have a major inflammatory component.
Several randomized trials have reported that taking alpha-linoleic acid supplements reduces the levels of inflammation markers, such as C-reactive protein (CRP) and interleukin 6. Taking omega-3 supplements also seems to be an effective way of alleviating the symptoms of rheumatoid arthritis, a systemic inflammatory disorder, that affects synovial joints. Patients suffering from the disease needed less non-steroidal anti-inflammatory drugs to cope with its symptoms when they took omega-3 fatty acid supplements.
Linoleic acid, on the other hand, has beneficial effects on serum lipid profiles. It decreases the levels of LDL cholesterol, and blood triglyceride levels, and hence protects against arterial plaque formation and atherosclerosis.
DHA, the alpha-linoleic acid derivative, and arachidonic acid, the linoleic acid derivative, are both important components of the phospholipids of cell membranes. Both the omega-3, and omega-6 long chain fatty acids are found in particularly high levels in the plasma membranes of cells of the gray matter in the brain. They are released from the membrane by phospholipidase enzymes which are activated by neurohormones and neurotransmitters and the free fatty acids exert their effects on the central nervous system by actin on neuron ion channels. They are also necessary for the synthesis of neural eicosanoids, which play a part in mood and behaviour. Essential fatty acids are now being actively investigated for their potential roles in preventing dementias like Alzheimer’s disease, and as treatments for mental illnesses such as bipolar depression.
The Anti-Oxidant Phytochemicals in Virgin Avocado Oil
Phytochemicals are various molecules of plant origin, which have potentially significant benefits for human health, mainly due to their anti-oxidant properties. They play different roles in plants, including their function as bright pigments (they are mostly found in intensely coloured fruits and vegetables), or as strong aromatics. They include carotenes, xanthophylls, polyphenols, phytosterols and others. Avocado fruits are particularly rich in a variety of phytochemicals, such as lutein, cryptoxanthin, and zeaxanthin, which are found concentrated under the skin, in the greener parts of the avocado flesh. Since phytochemicals are fat soluble they are extracted into the oil. However only virgin avocado oil is rich in phytochemicals, since they are removed in the refining process.
Research into the specific roles the different phytochemicals play in maintaining human health and protecting against disease is only just starting. So far we know that most of them are powerful anti-oxidants. Free radicals are created by the reactions of normal metabolism, but they are also caused by pollution, UV radiation from the sun, and contaminants in the food. Free radicals have an unpaired electron and are very unstable. The sometimes react to form reactive oxygen species which are also unstable and will readily oxidise lipids, proteins or DNA which leads to tissue and DNA damage.
The body, of course, produces its own antioxidants to deal with the free radicals. However, if the reactive oxygen species produced overwhelm the body’s natural defences, the result is oxidative stress.
Oxidative stress has been found to play a major factor in many diseases. The free radical damage to DNA can cause mutations which might lead to cancer. Damage to skin collagen results in aging skin, while oxidation of the proteins in neurones leads to cognitive difficulties and possibly dementia. Oxidative stress also plays a major role in heart disease and atherosclerosis, since it is the oxidation of LDL-cholesterol that leads to its phagocytosis by macrophages, the first step in plaque formation.
In decreasing oxygen reactive species, anti-oxidants from the diet play a crucial role in slowing down the aging process, and protection from heart disease. Recently scientists have discovered two fascinating mechanisms in which the phytochemicals in organic virgin avocado oil are able to fulfill this role particularly well.
One of the main metabolic sources of reactive oxygen species is cellular respiration, in which glucose is oxidised to produce energy in the form of ATP, and which takes place in the mitochondria. It appears that many antioxidants simply cannot enter the mitochondria, and hence cannot prevent the oxidative damage from free radicals to these essential organelles. On the other hand it appears that the antioxidants contained in avocado oil are able to be transported into the mitochondria, and can neutralise the free radicals at the site where they are produced.
The other advantage of consuming antioxidant caratenoids in avocado oil is that they have much higher bioavailability than phytochemicals from fruit and vegetables that are low in fat. The plant chemicals are lipid soluble, and when consumed as part of oil they can be absorbed in the intestine at a much higher rate, than when eaten without oil. In fact it was shown that the addition of avocado oil to fat-free salads improves the absorption of the phytochemicals from other vegetables, such as tomatoes.
As well as anti-oxidants Xbrain’s organic, virgin avocado oil, contains a high level of the phytosterol, beta-sitosterol. Sitosterols are plant chemicals that have a structure similar to cholesterol. Their effects on lowering serum LDL cholesterol levels are well documented. The mechanism of this effect is probably due to competition between them and cholesterol for binding sites. The FDA has approved the claim that regular consumption of sufficient beta-sitosterol can lead to a reduced risk of heart disease. The European Foods Safety Agency (EFSA), on the other hand, has concluded that daily consumption of sufficient phytosterols can reduce serum cholesterol levels by up to 7.5-10%. Hence the beta-sitosterol content of avocado oil contributes to its overall LDL-cholesterol reducing qualities.
The Glutathione Anti-Oxidant Content of Avocado Oil
Virgin avocado oil is also an excellent source of glutathione, a powerful anti-oxidant. Glutathione is a tripeptide, made up of the amino acids cysteine, glutamic acid and glycine. The thiol groups of cysteine are responsible for its anti-oxidant properties, since they can act as an electron donor to unstable reactive oxygen species. In the reaction glutathione, itself becomes unstable, but it reacts with another glutathione molecule to form glutathione disulfide, which is then recycled into the reduced state by the enzyme glutathione reductase.
Glutathione (GSH) is one of the main anti-oxidants produced by cells to combat oxidative stress. It is present in particularly high levels in the liver, and is a major player in the liver’s detoxification process. However the amount of GSH produced by the body is limited by the amount of the availability of the amino acid cysteine, which is rare in food. If the cells cannot synthesise sufficient GSH to cope with the free radicals produced by metabolism, or by air pollution, or UV radiation, oxidative stress results.
The ratio of the reduced form of GSH to the oxidised glutathione disulfide is often used as a measure of oxidative stress. In healthy tissue glutathione disulfide represents less than 10% of the total GSH pool.
As well as neutralising free radicals, GSH plays an important role in recycling other anti-oxidants, such as vitamins C and E into their reduced forms. It also plays an important role in the excretion of fat soluble toxins by the liver. Since it is a hydrophillic molecule, it has to be added to hydrophobic toxins, before they can be excreted in bile.
Avocado Oil is a Rich Source of Vitamin E
Alpha Tocopherol, commonly called vitamin E is also an important anti-oxidant. It helps protect against heart disease by inhibiting the oxidation of LDL cholesterol which leads to plaque formation and atherosclerosis. It is thought that it might protect against dementias, like Alzheimer’s disease, and age related eye disease such as macular degeneration, damage to the retina caused by glaucoma, and cataracts. It also acts as a natural preservative, protecting the fatty acids in avocado oil from oxidation.
Further Reading:
Nutritional analysis and benefits of avocado oil:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3664913/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3545982/
Nutritional benefits of oleic acid:
http://jn.nutrition.org/content/119/4/529.full.pdf
http://www.pnas.org/content/105/37/13811.long
http://qjmed.oxfordjournals.org/content/93/2/85.long
The benefits of polyunsaturated fatty acids:
http://www.nlm.nih.gov/medlineplus/druginfo/natural/993.html
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0041092/
http://lpi.oregonstate.edu/infocenter/othernuts/omega3fa/