Know your oils (Part 2)
published: Wednesday | July 21, 2004

Patricia Thompson - NUTRITION TALK

OILS MAY come from animals as with fish oils or from plants as with vegetable oils. Although they are all 100% fat and carry similar calorie values, all oils are not the same because they have different chemical structures that determine their properties and how they are best used.

CLEARING THE CONTROVERSY ABOUT OILS

The main controversy about fats and oils has been their relationship to cholesterol and heart disease. Fish oils such as cod liver and herring oils are the only oils that contain cholesterol, yet fish oils have been found to reduce the risk for heart disease. This is because they have a fatty acid called omega-3, which helps to thin the blood and prevent blood clotting, called platelet aggregation. In fact, the role of fish oils in protecting against heart attack and stroke seems more related to their action against platelet aggregation than their cholesterol lowering effect. Flaxseed oil has similar fatty acids and effects as fish oils. The platelet aggregation values for coconut oils are intermediate between the low values for fish oils and the high values for corn oil. The action of the polyunsaturated oils in reducing blood cholesterol levels seem related to their content of plant sterols or phytosterols that block the uptake of cholesterol (an animal sterol) in the gut. Corn and sesame oils have the highest phytosterol values with lower values from soy and olive. Coconut and palm oils have the lowest values.

THE REAL ISSUES

Since none of the oils raise cholesterol levels, what then are the real issues surrounding the oils? One important factor is the toxic potential and their ability to either promote or control infection and inflammation. Inflammation is associated with free radical production and disease causation such as cancer, diabetes, arthritis etc. Canola oil is made from rapeseed, which was originally used as industrial engine oil and is toxic to humans. Although the modified product does not raise cholesterol levels, there are questions about the safety of its contaminants.

Polyunsaturated oils are sensitive to heat and are best used raw, since heating damages them and leads to free radicals that attack weakened cell membranes, leading to premature ageing and disease. In their natural state i.e. undamaged by processing they provide raw material for the production of prostaglandins, hormone-like compounds that play a major role in protecting the cardiovascular, reproductive, immune and central nervous systems.

THE EFFECTS OF COOKING AND PROCESSING

The higher the temperatures that oils are subjected to the greater the damage. Sunflower and safflower oils for example should not be used in cooking but can be added to salad dressings or at least in tossing steamed vegetables. In fact once you open these oils, they should be refrigerated to protect from excess heat, air and light.

The saturated nature of coconut oil makes it non-reactive so that even when hydrogen is added as when making margarine, there is no change in its structure to form the toxic trans-fatty acids as occurs when soy oil is the main ingredient. Coconut oil has the highest smoking point and is therefore the best choice if you must fry foods. To get the best quality oil, the manufacturing process should be considered. Cold pressed coconut, peanut or olive oils known as 'virgin oils' are more natural than heat pressed and 100% expeller-pressed on the label is one indication that no heat was used in processing.

A well balanced diet with moderate intakes of fats and oils will provide the most health benefits.

Patricia Thompson M.Sc., registered nutritionist, nutrition and diet services; email: yourhealth@gleanerjm.com.