Presentation on theme: "Lipids Iva Klimešová. Like carbohydrate, a lipid molecule is composed of carbon, oxygen, and hydrogen atoms linked together in a specific and unique way."— Presentation transcript:
Like carbohydrate, a lipid molecule is composed of carbon, oxygen, and hydrogen atoms linked together in a specific and unique way. There are three different functions for lipids in our bodies: Energy source Energy storage Forming the membranes around our cells. Providing the starting material (cholesterol) for making hormones Carrying the fat-soluble vitamins (A, D, E and K) and carotenoids) The largest amount of energy is stored in the body as fat. Lipids contain a lot of calories in a small space.
Fats are stored as triglycerides in both the muscle tissue and adipose (fat) tissue. Essentially, a lipid molecule consists of one glycerol molecule and three fatty acid molecules to form triglyceride. Fatty acids have two unique characteristics: 1.the length of their carbon chain (Food contain fatty acids with chain length of 4 to 24 carbons.) 2.the bonding of carbon atoms
The length of carbon chain: Short-chain fatty acids (SFA) have 4 to 8 carbons; sources: milk and dairy produce (SFA are the major end products of bacterial metabolism in the human large intestine.) Medium-chain fatty acids (MFA) have 9-12 carbons; sources: milk and dairy produce, coconut and palm oil Long-chain fatty acids (LFA) have more than 12 carbon; source: many animal fats The shorter the carbon chain, the more liquid the fatty acid becomes (the lower its melting point). Oils are usually of the short-variety. Shorter fatty acids are more water-soluble, a property that affects their absorption in the digestive tract.
The bonds of carbon chain saturated fatty acids with only single bonds linking carbons together H H H H OH R - C - C - C - C - C = O H H H H glycerol
unsaturated fatty acids with at least one double bonds in the carbon chain –Monounsaturated (a fatty acid in which the carbon chain contains one double bond) –Polyunsaturated (a fatty acid in which the carbon chain contains two or more double bonds) H H H H H H OH R - C = C - C - C = C - C - C = O H H glycerol
There are different types of fatty acids in one molecule of triglyceride. Regardless of the degree saturation, all lipid have essentially the same number of calories per unit weight. The American Heart Association has set guidelines for triglyceride levels in blood: Level mg/dLmgdLLevel mmol/LmmolLInterpretation <150<1.69Normal range, lowest risk of CVD 150-1991.70-2.25Borderline high 200-4982.25-5.63High level, high risk of CVD >500>5.65Very high, increased risk of CVD
Saturated fats At room temperature, saturated fats are usually solid. Source: primarily in animal products including beef, lamb, pork and chicken, egg yolk, dairy fats of cream, milk, cheese, butter; coconut and palm oil; non-dairy creams because they contain coconut oil Consumption of saturated fats has been linked with risk of coronary heart disease: –sources of saturated fat are full of cholesterol (except coconut and palm oil) –diet high in saturated fat facilitates cholesterol synthesis by the liver (including coconut and palm oil)
Unsaturated fats At room temperature, unsaturated fats are usually liquid. Monosaturated Sources: olive, peanut, canola, rape oil, almonds, avocado Polyunsaturated Sources: sunflower, soybean, corn, and safflower oil, fish oil, walnuts, sesame seeds, pumpkin seeds, tofu, lard Unsaturated fatty acids are sensitive to heat and light damage – store them in the dark bottles and use for cold or short hot preparations
Humans and other mammals can synthesize saturated and some monounsaturated fatty acids from carbon groups in carbohydrate and protein. Polyunsaturated fatty acids an omega-3 fatty acid and an omega-6 fatty acid are considered essential fatty acids (because they cannot be synthesized by humans). Essential fatty acids: omega-3 The parent fatty acid of the omega-3 series is alpha-linolenic acid (ALA) (ALA contains 18 carbon atoms and 3 carbon-carbon double bonds, 18:3). ALA- humans can synthesize eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from ALA Sources: flaxseed oil, soybean oil and canola oil, nuts, seafish – salmon, herring, sardine, tuna omega-6 The parent fatty acid of the omega-6 series is linoleic acid (LA) (LA contains 18 carbon atoms and 2 carbon-carbon double bonds, 18:2). LA - humans can synthesize dihomo-gamma-linolenic acid (DGLA) and arachidonic acid (AA) from LA Sources: olive and sunflower oils, sesame, pecans, pine nuts, freshwater fish – carp, trout, catfish, eel
Clinical signs of essential fatty acid deficiency decreased growth in infants and children, increased susceptibility to infection and poor wound healing. Omega-6 and omega-3 PUFA are important structural components of cell membranes, they are important to central nervous system function, and they play important roles in vision. Typical Western diets tend to be much higher in omega-6 fatty acids than omega-3 fatty acids. It has been estimated that the ratio of omega-6 to omega-3 fatty acids in the diet of early humans was 1:1, but the ratio in the typical Western diet is now almost 10:1 due to increased use of vegetable oils rich in LA and declining fish consumption. Omega-3 intakes are associated with significant reductions in cardiovascular disease risk, the American Heart Association recommend that all adults should eat fish, particularly oily fish, at least twice weekly.
A large body of scientific research suggests that increasing the relative abundance of dietary omega-3 fatty acids may have a number of health benefits. Increasing EPA and DHA intake may be beneficial to individuals with diabetes, especially those with elevated serum triglycerides.
Approximate percentage of fatty acids in common fats and oils
Cis Versus Trans Otherwise identical unsaturated fatty acids can have different shapes. The carbon chain of a cis fatty acid is bent, and the chain of a trans fatty acid is straighter. Most naturaly occuring unsaturated FA are cis FA.
Trans-unsaturated fatty acids (TFA) TFA are product of hydrogenation which increases the saturation of fatty acids within oils and converts natural cis to trans configuration Hydrogenation= industrial process that chemically transforms a low melting point oil into a solid fat with a higher melting point to enhance product taste, stability and shelf life. Found in commercially fried foods (French fries, popcorn), commercial baked goods and snacks (cakes, cookies, biscuits), margarine, and cheap vegetable shortenings (not in e.g. Flora, Rama). Trans-fatty acids have many adverse metabolic effects including elevation of LDL („bad“) cholesterol, triglycerides, reduction in HDL („good“) cholesterol, and adverse effects on endothelial function, inflammatory markers, and probably insulin resistance.
The diet in northern European countries has traditionally contained more trans-fatty acids than the diet in Mediterranean countries in which olive oil is commonly used. Mean daily intakes of trans-fatty acids in European countries range from minimal values in Italy, Portugal, Greece and Spain to greater values for Germany, Finland, Denmark, Sweden, France, United Kingdom, Belgium, Norway, the Netherlands, and Iceland. Recent decreases in the trans content of the diet have been observed, presumably due to modifications of commercially available fats or changes in consumer choices. Today, most margarines in the European market have a lower content of trans fatty acids than 5 to 10 years ago and in most cases the change has been carried out without adverse effects for the consumer. The technologies used here are now implemented in a number of other industries. New technologies have been adopted to solve specific problems in, for example, the bakery and chocolate confectionery.
Cholesterol Cholesterol is non-fat substance vital to human metabolism, and although it may be obtained in the diet only from animal foods, the body can produce its own way. The recommended cholesterol intake is less then 300 milligrams per day (the richest source is egg yolk has 220 mg). A positive relationship has been established between high blood cholesterol levels and coronary heart disease, reduction of dietary cholesterol has been advocated by a number of health recommendations. Fruits, vegetables, grains, and nuts have no cholesterol.
Recommendation is that total daily fat intake be limited to < 30% of total daily energy intake with no more than 10% provided by saturated and trans fats, polyunsaturated fatty acids should be limited to no more than 10% of total daily energy intake ( Because polyunsaturated fatty acids may also lower HDL- cholesterol as well as LDL-cholesterol) 10% provided by monounsaturated fats
Digestion and absorption Digestion of fats starts in the stomach by the action of linqual lipase, an enzyme secreted in the mouth. This enzyme digests short- and medium-chain saturated fatty acids. The stomach secretes gastric lipase which works with linqual lipase to digest a very small amount of fat. The major breakdown of lipid occurs in the small intestine. The fat is emulsified into very small droplets by the action of bile (secreted from gallbladder) - it facilitates enzyme action. Pancreatic lipase, the main fat-digesting enzyme, degrades some of the triglyceride molecules to monoglycerides and fatty acids. In this simpler form, monoglycerides are more easily absorbed by the intestine. The absorbed glycerol, fatty acid, and monoglyceride molecules are then free to recombine to reform triglycerides.
The fatty acids take one of two routes depending on their chain length: –Short- and medium-chain fatty acids proceed to the portal vein and empty into the liver. –Long-chain fatty acids and cholesterol is first reconverted to a chylomicron and then transported through the lymphatic system into the systemic vein that empty into the heart.