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Oils and fats provide about 9 kcal/g of metabolisable energy compared to 4 kcal/g from protein or carbohydrates. In addition to their caloric and nutritional value, oils and fats carry, enhance and release the flavours of other foods, as well as increase palatability. Oils and fats are a good carrier of Vitamins A, D, E and K with excellent bioavailability.

Polyunsaturated fatty acids (PUFA) cannot be synthesised in the body; therefore, oils and fats supply an excellent source of these essential fatty acids (EFA). Saturated and monounsaturated fatty acids are also very important for several vital functions of the body.

For these reasons, oils and fats and different types of fatty acids should now be considered key nutrients that affect early growth and development, as well as nutrition-related chronic diseases later in life.

Oils and fats are structural bodily components; they are involved in vital physiological processes, including growth, development, inflammation and brain function. Combinations of lipid and protein (lipoproteins) are important cellular constituents, occurring both in the cell membrane and in the mitochondria, and further serve as a means of transporting lipids in the blood.

Every oil is unique

Globally, the nine major oils consumed are palm, soybean, rapeseed, sunflower, peanut, palm kernel, cottonseed, coconut and olive oils. Various other oils and fats are also consumed depending on local priorities and availability. All the dietary oils and fats are composed of a mix of polyunsaturated, monounsaturated and saturated fatty acids.

Omega-6 and Omega-3 fatty acids are essential fatty acids commonly known as PUFA; their deficiency may cause several health problems like cardiovascular disease, diabetes, cancer and age-related functional decline.

High amounts of Omega-6 fatty acids, namely linoleic acid (LA), are present in corn, soybean, sunflower, safflower, cottonseed and sesame oils, among others. Omega-3 fatty acids, namely linolenic acid (LnA), are found in select sources like flax seed, soybean and mustard oils.

Fish oil is a unique source of long chain Omega-3 fatty acids, namely eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Over the last decade, some algal oils have been produced as a source of EPA and DHA.

EFAs, namely LA and LnA, are involved in many physiological processes and vital functions such as blood clotting, wound healing and inflammation; they also convert to longer chain fatty acids like arachidonic acid, EPA and DHA. They are further converted to compounds such as prostaglandins, thromboxanes, lipoxin, resolvins and leukotrienes, with hormone-like or inflammatory properties.

PUFA are known for lowering blood total and LDL-cholesterol and slightly increasing HDL-cholesterol. Monounsaturated fatty acids (MUFA) are found in olive, canola, peanut, rice bran, mustard, high oleic sunflower and soybean oils, and are part of animal fats such as chicken, pork and beef. MUFA have a blood total and LDL-cholesterol-lowering effect.

Saturated fatty acids (SFA) are found in the greatest amounts in palm, coconut and palm kernel oils, as well as in cocoa butter, butter and animal fats like beef, pork and chicken. SFA increase blood total, LDL-cholesterol and HDL-cholesterol concentrations and decrease fasting triglyceride concentrations.

Determinants of properties

The fatty acids in oils and fats not only dictate the nutritional properties but also the physical characteristics. The unsaturated fatty acid content of vegetable oils determines their fluidity and other physical and chemical properties of relevance to the food industry.

Oils rich in MUFA are preferred for frying as they are more heat resistant. Oils and fats rich in SFA exhibit higher solid fat content, a property that is required in some food applications (like consistency of fat spreads or formation of layers in pastry), in addition to frying applications.

Oils and fats can also be fingerprinted based on specific nutritional components. For example, palm and rice bran oils contain tocotrienols; palm oil contains beta carotene; rice bran oil contains oryzanol; sesame oil contains lignans; soybean oil contains gama tocopherols; and sunflower oil contains alpha tocopherols.

Several oils are projected as healthy oils based on the presence of these nutritional components.

Dr RBN Prasad
Platinum Jubilee Mentor & Former Chief Scientist
Centre for Lipid Research
CSIR-Indian Institute of Chemical Technology
Hyderabad, India