Friday, April 18, 2014

Nutritive value of dietary lipids

Lipid is a collective name for fats, fatty acids, oils and steroids. A lipid is an organic substance made up of carbon, hydrogen and oxygen that is not soluble in water.  The basic unit of lipids is a triglyceride synthesized from glycerol and fatty acids. Lipid is an essential dietary constituent in human nutrition because of its high calorific value (9 calories/gram). Lipids provide energy and help the body use vitamins. Lipids are essential for cell integrity and survival. Lipids are found in all cells of the body.
  WHO (2003) recommended the total fat intake for adults from the minimum (ideal) of 15 – 20% to a maximum of 30 – 35% for most individuals. The French, Greeks, Spanish, Inuit, Masai of Africa, Swiss and other cultures have thrived on diets with over 40 percent of calories from fat, much of it animal fat. Lipids are widely distributed in plants and animals.  Plants often store lipids in fruits and seeds. The form of lipids stored in animal tissues is varying widely in both quantity and type. The predominant substances in fats and oils are triglycerides.  Generally lipids are stored in adipose tissue, mesenteric tissue, and yellow bone marrow and around organs like kidney. The nervous system is rich in lipids like cholesterol, phospholipids and glycolipids. Dietary lipids supply essential fatty acids (EFA) to the body. They resemble vitamins and they cannot be synthesized by the body. Dietary lipids provide the medium for the absorption of fat soluble vitamins (vitamins A, D, E and K); a primary contributor to the palatability of food and are crucial to the early embryonic development.  Lipids serve as the concentrated fuel reserve ( e.g., triacyl glycerols) of the body and  the important  constituent of cell membranes and sex hormones.

 Dietary fat disorders

Nutrient deficiency in fat intake may cause the deficiency of essential fatty acids (EFAs).  EFAs are very important nutritional requirements for keeping good health. The deficiency of EFAs may increase the risk of getting affected by cancer, atherosclerosis, coronary heart disease, behavioural problems and chronic inflammation.
Nutrient imbalance   of fatty acids may result from the consumption of diets rich in omega – 6 and diets deficient in omega – 3 fatty acids. Excessive amounts of omega – 6 poly unsaturated fatty acids (PUFA) and a very high omega-6/omega-3 ratio, as is found in today’s Western diets, promote pathogenesis of many diseases including cardiovascular disease, cancer, and inflammatory and autoimmune diseases.
Nutrient excess diseases – eating excess calories causes fat to build up in the liver. It is a common liver complaint in Western countries. It affects about one in every 10 people.  The fatty liver disease leads to inflammation and liver damage. This condition is called non-alcoholic steatohepatitis, NASH or non-alcoholic fatty liver disease, NAFLD. The people with NAFLD have an increased risk of cardiovascular problems such as heart attacks and strokes.
Obesity means having too much of body fat. Obesity has been increasing rapidly throughout the world and incidence of obesity nearly doubled from 1991 to 1994.  Over two-thirds of adult in the United States are over-weight or obese and one in three Americans is obese. Being obese increases one’s risk of diabetes, heart disease, stroke, arthritis and some cancers.
Toxic fat syndrome (TFS) – is an epidemic primarily caused by a combination of 3 conditions: increased dietary bad fat consumption ( trans and high omega 6-fats), increased high glycaemic carbohydrate consumption(simple and starchy) and decreased dietary omega 3 fat consumption. TFS is the growing levels of toxic (soluble e.g., arachidonic acid,AA) fat in the blood stream. This toxic fat increases silent (deadly) inflammation, which is the cause of most diseases and chronic illness.

Dietary fats

 There are 3 different kinds of fats in foods such as saturated, unsaturated and transformed (trans) fats.  The saturated and transformed fats are called unhealthy or bad fats because the dietary intake of these fats contributes to increase cholesterol in the blood.  The dietary intake of unsaturated fats helps reduce cholesterol levels in the blood and so they are called healthy or good fats. The foods rich in saturated fats include butter, cream, bacon, palm oil and red meat. Saturated fats are solid at room temperature and come from both animal and plant sources. Animal sources are butter, lard (pork fat), suet (beef fat) or tallow, meat and poultry (especially the skin) and high-fat dairy products. Plant sources include palm, palm kernel and coconut oils, often found in commercial baked goods. Too much saturated fat can cause blood cholesterol levels to rise. Most foods contain a combination of saturated and unsaturated fats with one type of fat usually found in higher amounts.
 Fatty acids are long chain organic acids having usually from 4 to 30 carbon atoms. They have a single carboxyl group and a long non-polar hydrocarbon tail. Fatty acids represent 30–35% of total energy intake in many developed countries and the most important dietary sources are vegetable oils, dairy products, meat products, grain and fatty fish or fish oils.  Saturated and unsaturated fats have different chemical structures but contain the same number of calories per gram. The unsaturated fats are of two types: monounsaturated and polyunsaturated fats. Monounsaturated fat is found mainly in avocado, nuts and vegetable oils (canola, olive and peanut oils). This fat may help lower bad ‘LDL cholesterol’ and lower the risk of heart disease. Polyunsaturated fat is mainly found in vegetable oils (safflower, sunflower, sesame, soybean and corn oil)  and sea foods. Polyunsaturated fats are further divided into omega-6 polyunsaturated or omega-3 polyunsaturated fats and this terminology refers to the position of the double-bonds in the molecule. Omega -3 fatty acids are found in plants –soybean oil, canola oil, walnuts and flaxseeds. They are also found in fatty fish and shellfish as EPA and DHA. Salmon, anchovies, herring, sardines, trout, Atlantic mackerel, Pacific mackerel and Pacific oyster are high in EPA and DHA. Omega-6 fatty acids are found mostly in liquid vegetable oils like soybean oil, corn oil, and safflower oil.
Trans fats (transformed fatty acids) are formed during the process of hydrogenation of vegetable oils. This process is done to extend the shelf life of the food and stop the oil from spoiling. Shortenings and some margarines are produced by the hydrogenation process.Many commercially produced foods can have trans fats. This includes prepared cookies, crackers, cake, pizza dough, doughnuts, biscuits, refrigerated doughs, fried foods, and french fries. Small amounts of trans fats occur naturally in meat from ruminant animals well as in dairy products. Foods such as cakes, cookies, crackers and other snack foods often contain trans fats in the form of hydrogenated vegetable oil. Research claims that trans fats may increase LDL or bad blood cholesterol levels.

Management of  body fats

Fats have traditionally been recommended for minimal consumption. Saturated fat should be NO more than 7% of total calories. Trans fats from deep fried fast foods, cookies and snack foods should be reduced to the absolute minimum. Dietary intake of omega-3 fats is associated with a 40-65% reduced risk of death from cardiac events.Omega-3 fats may reduce the risk of heart rhythm problems and at high doses, reduce triglyceride levels. Studies have suggested that omega - 3 fats reduce the risk for heart attack and death from heart disease for those who already have heart disease (National Cholesterol Education Programme, 2001).  

Nutrition and food pyramids

Food pyramids are tools one can use to guide or assess dietary intake. Pyramids allow a person with limited nutritional knowledge to make sound decisions about what foods to eat.  The larger base of the pyramid represents the types of foods one should consume more often while the smaller top of the pyramid represents foods one should consume less frequently.

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