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Fats are macronutrients requirement for the growth and development of the human body. Fats are solidified at a temperature of 20 degree centigrade and are called oils if they remain liquid at that temperature. Fats and oils are concentrated sources of energy. They are classified into two types:
Simple lipids: These include triglycerides.
Compound lipids: These comprise of phospholipids and derived lipids including cholesterol.
The human body can synthesize triglycerides and cholesterol endogenously. Most of the body fat (99%) in the adipose tissue is in the form of triglycerides. In normal human individuals, adipose tissue constitutes between 10-15% of body weight. The accumulation of 1 kg of adipose corresponds to 7700 kcal of energy.
Fatty acids: Fats yield fatty acids and glycerol on hydrolysis. Fatty acids are divided into saturated fatty acids such as lauric, plamitic and stearic acids and unsaturated fatty acids which are further divided into monounsaturated (oleic acid) and polyunsaturated fatty acids (linoleic acid). The poly unsaturated fatty acids are mostly found in vegetable oils and the saturated fatty acids are mainly found in animal fats. Coconut and palm oils, although vegetable oils have an extremely high percentage of saturated fatty acids. Fish oils although not vegetable oils, contain poly and mono unsaturated fatty acids.
Essential fatty acids: Essential fatty acids are those that cannot be synthesized by humans. They can be derived only from food. The most important essential fatty acid is linoleic acid, which serves as the basis for the production of other essential fatty acids such as linolenic and arachidonic acids. Not all polyunsaturated acids are essential fatty acids. Linoleic acid is abundantly found in vegetable oils such as corn oils, sunflower oil, soybean oil, groundnut oil, mustard oil, coconut oil etc. Arachidonic acid is found in meat, eggs and milk fat. Linolenic acid is found in soybean oils and green leafy vegetables
Sources of Fats:
The dietary sources of fats are classified into:
Animal Fats: The major sources of animal fats are butter, milk, cheese, eggs and fat of meat and fish. Animal fats with few exceptions like cod liver oil and sardine oil are mostly saturated fats.
Vegetable Fats: Some plants store fats in their seeds such as groundnuts, mustard, sesame, coconut etc. They are sources of vegetable oils.
Other Sources: Small quantities of fat are found in most other foods such as cereals, pulses, nuts and vegetables.
Functions of Fats: Fats have always been equated with calories. They are the preferred sources of energy for the body. By supplying energy, they spare proteins from being used for energy. Fats also serve as a means for the absorption of fat-soluble vitamins. Fats support the functioning of the heart, kidney and intestine. The fats beneath the skin provide insulation against cold.
Non-caloric roles of fats:
Vegetable fats are rich sources of essential fatty acids which are needed by the body for growth, maintaining the structural integrity of the cell membrane and decreased platelet stickiness.
Diets rich in essential fatty acids reduce serum cholesterol and low density lipoproteins.
Polyunsaturated fats are precursors of prostaglandins – a group of compounds also known as local hormones. They play a major role in controlling many of the physiological functions of the body such as vascular homeostasis, kidney function, acid secretion in stomach, gastro-intestinal motility, lung physiology and reproduction.
Cholesterol is essential as a component of membranes and nerve tissues and is a precursor for the synthesis of steroid hormones and bile acids.
Fats and diseases:
Obesity: A diet, rich in fat, can pose a threat to human health by encouraging obesity. In fat people, adipose tissue may increase up to 30%.
Coronary heart diseases: High fat intake including dietary fat representing 40% or over of the energy supply and containing a high proportion of saturated fats has been identified as a major risk factor for coronary heart disease. Studies indicate that LDL and VLDL fractions are atherogenic and HDL exerts a protective effect against the development of atherosclerosis. There is evidence indicating an inverse relationship between essential fatty acid intake and CHD mortality.
Cancer: In recent years, there has been some evidence that diets high in fat increase the risk of colon cancer and breast cancer.
Fat requirements
In developed countries, dietary fats provide 30 - 40 % of total energy intake. The WHO Expert committee on Prevention of Coronary Heart Disease has recommended only 20-30% of total dietary energy to be provided by fats. At least 50% of fat intake should consist of vegetable oils rich in essential fatty acids.
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