Summary
A large body of scientific evidence supports a move from the traditional Western diet, rich in saturated fat and sugars, to one similar to that consumed in the Mediterranean area, as being more healthful. Avocado oil has a composition closely resembling olive oil and can be directly substituted for it in a healthful cuisine.
Introduction
Cold pressing of avocados produces very high-quality oil with very low levels of acidity and oxidation products whilst retaining the vitamin E content.(Eyres et al 2001)
Avocado oil has very desirable qualities as a food oil, but does it bring health benefits? While there may well be constituents not yet explored, several have defined health effects. The oil is very similar to olive oil, which is a basis of the healthful Mediterranean diet, the key similarity being that Avocado oil is very rich in monounsaturated fatty acids and extremely low in saturated fat. It also contains no cholesterol.
Raised blood cholesterol level - Effect of monounsaturates
An elevated level of blood (low density lipoprotein, LDL) cholesterol is an established risk factor for coronary heart disease (CHD). This led to the popular media describing it as the "Bad" cholesterol. Early work in the 1950s suggested that diets rich in fat and cholesterol were associated with the rising prevalence of this disease. The Framingham population study identified raised blood cholesterol levels [now known to be LDL] as one of the major risk factors.
It was broadly believed that saturated fats raised blood (LDL) cholesterol levels, polyunsaturates [later changed to omega-six polyunsaturates] reduced those levels, and monounsaturates were neutral.
Subsequent work showed that this was not correct, and that monounsaturates actually did lower LDL cholesterol. A variety of hypotheses were formed. Although ultimately a whole host of potential candidate components of the diet were described, the fact that the main fat component, olive oil, was predominantly a monounsaturated fat was a probable explanation. A diet proportionally high in monounsaturates has also been recently proposed as suitable for diabetics so long as other factors such as exercise and sufficient fruit and vegetables are included in the so called Mediterranean protocol.
Table 1 Fatty Acid Composition of Food Oils
|
|
| Omega-9 | Omega-6 | Omega-3 |
| Food | Stats | MUFA (oleate) | Linoleate | a-linolenate |
| Avocado oil | 13.4 | 72 | 9 | 0.5 |
| Olive oil | 17.3 | 66.8 | 11.8 | 0.6 |
| Peanut butter | 21.6 | 51.6 | 26.2 | - |
| Maize oil(corn oil) | 17.2 | 28.7 | 47.8 | 1.5 |
| Canola oil | 7.8 | 58.2 20.8 | 10.1 |
|
| Wheat germ oil | 20.1 | 15.4 | 53.6 | 10.4 |
| Almonds | 8.3 | 70.9 | 19.1 | 0.5 |
NB Avocado is even lower than olive in saturated fatty acid content
MUFA abbreviated form of monounsaturated fatty acids
Substitution of monounsaturates for saturates even without a change in total fat will result in a substantial reduction in LDL cholesterol level.
Effect of phytosterols (Beta Sitosterol)
Food cholesterol is absorbed into the body along with other food lipids, but some of it is excreted back into the intestine in the bile, along with cholesterol-derived compounds called bile acids. These various sterols can then be reabsorbed further down the intestine, forming an excretion/reabsorption cycle.
A considerable number of such phytosterols have been studied, as they are quite widely distributed in plant foods. Quantitatively the most significant has been beta-sitosterol, but campesterol and stigmasterol are also present in many foods. Phytosterol content of several foods is given in Table II.
Table II Beta-Sitosterol levels of plant oils
| Source | Range % | Typical % |
| Avocado Oil | 0.4 - 0.9 | 0.5 |
| Saw Palmetto | 0.2 - 0.5 | 0.3 |
| Olive Oil | 0.2 - 0.3 | 0.25 |
| Sterol Spread | 8.0 | 8.0 |
In almost all people phystosterols are nontoxic. Safety studies on phytosterols by various regulatory agencies show that there are no significant safety issues even with more than 2g/d intake.
Absorbed sitosterol has beneficial effects in increasing plasminogen activation [which is depressed by cholesterol], and also seems to enhance conversion of linoleate to other essential polyunsaturated fatty acids. These effects are likely to have a beneficial effect on risk of CHD.
Other health benefits of phytosterols
Sitosterol has been used in the management of a variety of other conditions, notably benign prostatic hypertrophy as carried out in a trial reported in The Lancet and in fact is the basis of drugs sold in Germany for this purpose. There is evidence that phytosterols may reduce the risk of prostate cancer at least in animal models.
Vitamin E
Vitamin E actually represents a mixture of at least eight compounds, called tocopherols and tocotrienols.
Several studies, especially a longitudinal one involving tens of thousands of subjects, reported there was a clear negative correlation between dietary vitamin E intake and risk of coronary heart disease. The reduction of risk was around 30-40%. Among those taking supplements, there was a greater benefit except for those at the highest levels, where there was less benefit.
It is well known that Vitamin E plays a role in aiding skin appearance and it is interesting and logical to speculate that a healthy oil diet containing this vitamin will assist in having a good complexion!!!
Lipid oxidation products
One aspect of food oils, which is often forgotten, is the propensity to being oxidized. Polyunsaturated fatty acids especially are prone to air oxidation. The adverse sensory properties of oxidized lipids has led to a need to add artificial antioxidants to some seed oils, although any benefit is often negated by exposing them to light in clear containers. Oils should optimally be sold in dark bottles, with instructions to store in the dark, and preferably kept under nitrogen until used.
It is not widely recognized however that lipid oxidation products have adverse health effects as well. Indeed a major defense system in the body works hard to prevent lipid oxidation whether that be lipids in cell structures or in the circulation.
New Zealand avocado oil has very low peroxide values, indicating that there has been very little oxidation, and is bottled under nitrogen in dark bottles.
Chlorophyll
Virgin avocado oil is distinctly green due to a high chlorophyll content (40-60mg/kg). While this might pose a risk of oxidative effects when exposed to light, earlier moves to decolorize the oil showed that consumers like the presence of chlorophyll, which is credited with health benefits. The rich colour of the avocado oil is due to a combination of the chlorophyll and lutein.
Summary and conclusions
This paper demonstrates that avocado oil, carefully prepared and stored, contains components which can bring many health benefits, while also providing the sensory and culinary benefits expected of a food oil. The oil because of its nutritional benefits is an excellent contributor to a healthy and balanced diet and is of particular benefit in diets which help to prevent coronary heart disease, diabetes and possibly prostrate problems.
Dr. John Birkbeck is professor of nutrition at Massey University (previously Otago) and has been seen as an expert in his field for many years.
References
Gey KF, Brubacher GB and Stahelin HB: Plasma levels of antioxidant vitamins in relation to ischemic heart disease and cancer. Am J Clin Nutr 1987;45:1368-1377.
Watts GF, Lewis B, Brunt JNH, Lewis ES, Coltart DJ, Smith LDR, Mann JI and Swan AV: Effects on coronary artery disease of lipid-lowering diet, or diet plus cholestyramine, in the St Thomas' Atherosclerosis Regression Study (STARS). Lancet 1992;339:563-569.
Kromhout D: Diet and cardiovascular diseases. J Nutr Hlth and Aging 2001;5:144-149.
Eyres L, Sherpa N and Hendriks G: Avocado oil: a new edible oil from Australasia. Lipid Technol 2001;Vol 13, no 4:84-88.
By John Birkbeck
