Lipids: Macronutrients 3 _Lipids 23-24 PDF

LIPIDS Need for Fat in Diet No specific requirement (apart from the essential fatty acids) but nutritionally important Difficult to eat enough of a low-fat diet to meet energy requirement 4 of the vitamins A,D, E and K are fat-soluble Many foods – flavour and therefore desire to eat comes from fat F...

LIPIDS Need for Fat in Diet No specific requirement (apart from the essential fatty acids) but nutritionally important Difficult to eat enough of a low-fat diet to meet energy requirement 4 of the vitamins A,D, E and K are fat-soluble Many foods – flavour and therefore desire to eat comes from fat Fat lubricates food – easier to chew and swallow NOTE: early recommendations – low fat diet Result – increased consumption of refined grains and added sugars Data now – type of fat is a more important risk factor than the total amount of fat Lipids in the Diet Lipids are organic molecules, most of which do not dissolve in water. Lipids contribute to texture, flavor, crispness and aroma of our food. Also contribute juiciness and tenderness Some lipids are obvious in food, some are hidden (butter vs cakes) Lipids contribute to about 33% of the energy in the typical American diet. Caution with the Fat free labels Fat free = less than 0.5 g fat/serving Low-fat = 3g or less /serving Reduced-fat = < 25% of natural counterpart “light” must have 1/3-50% the fat of regular product To compensate for lack of flavour –other components added  May contribute to calorie content May encourage to eat more rather than less Check what the brand establishes as “a serving” Ratings such as those opposite should be taken with caution Types of Lipids—Triacylglycerol (Triglyceride) Most commonly found in food and in body storage Properties determined by fatty acids they contain 5-9 Fatty Acids Different Unsaturated Fatty Acids Omega-3 (-3) and Omega-6 (-6) Fatty Acids 5-11 Different Unsaturated Fatty Acids Cis and Trans Fatty Acids Hydrogenation Behave like Sat Fas Raise melting point/lengthen shelf life Elevate LDL-C and lower HDL-C –Increasing risk of CHD 2018 – should be eliminated 5-13 Trans-Fatty acids Hypothesis – cause inflammation – increasing the risk of CHD. Inflammation is an important risk factor in the development of atherosclerosis Trans-fatty acids do not fit into cell membranes in the same way as do cis-isomers Two Essential Fatty Acids Must be consumed in the diet – – – – Linoleic acid (-6) and alpha-linolenic acid ( -3) Ratio important 6- important for growth/skin integrity/fertility/RBC structure 3-important for structure and function of cell membranes –eye and CNS Precursors for Eicosanoids (prostaglandins) – Regulating blood clotting, blood pressure, immune function, and other body processes −3 and −6 FA are precursors of eicosanoids Eicosanoids are: prostaglandins prostacyclin thromboxanes, Leukotrienes lipoxins. They act as local paracrine factors and exhibit a wide range of physiological actions, including: Lowering of blood pressure Diuresis platelet aggregation Effects on the immune and nervous systems gastric secretions; fever, inflammation and pain Biological effects of -3 fatty acids -3 FAs in the human body: a-linolenic acid, eicosapentoenoic acid (EPA) and docosahexoenoic acid (DHA). -3 FA are required for eicosanoid (prostaglandin, leukotriene) synthesis Sources of alpha-linolenic acid: – some seed oils (e.g. linseed oil, rapeseed oil, soya oil, walnut oil), but typically seeds contain omega 6 fatty acids. – meat from grass-fed animals (e.g. beef) – green leafy vegetables (e.g. spinach). – The very long chain derivatives: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are found predominantly in fish oils, in the flesh of oil-rich fish such as mackerel, salmon, herring, trout and sardines (but not in farmed fish). Omega-3 FA substantially reduce the risk of a fatal heart attack. – 1 gram per day of −3 fatty acids reduced the occurrence of death, cardiovascular death, and sudden cardiac death by 20%, 30%, and 45%, respectively. – The mechanism for their effect however thought not to involve reduction of blood cholesterol. – The very long chain -3 fatty acids (EPA and DHA, but not linolenic acid) lower blood TAG concentrations thus reduces the development of atherosclerosis. – All three -3 FAs have a beneficial effect on vascular function: protect against cardiac arrhythmias, which can cause sudden cardiac death. -3-FA have also been shown to thin the blood, and decrease inflammation (protection from arthritis). The effect of omega-3 FA on cancer is not proven sufficiently yet. Omega 3s Vital part of cell membranes Important in all cell – concentrated in high levels in cells of the eyes and brain Biological effects of -6 fatty acids -6 FA are required for eicosanoid (prostaglandin, leukotriene) synthesis −6 FA – no conclusive evidence from the literature that they have a role in preventing heart disease −3 and −6 FA compete for the same metabolic enzyme (COX), thus the −6:−3 ratio will dictate the ratio of the generated eicosanoids. This necessitates that −3 and −6 be consumed in a balanced proportion; healthy ratios of −6:−3 range from 1:1 to 1:4 Typical Western diets provide ratios of between 10:1 and 30:1 of −6 to -3. The ratios of −6 to −3 FAs in some common vegetable oils are: canola 2:1, soybean 7:1, olive 3–13:1, sunflower (no −3, 75% −6), flax 1:3, cottonseed (almost no −3), peanut (no −3), grapeseed oil (almost no −3) and corn oil 46:1 ratio of −6 to −3. Dose responses of physiologic effects of fish oil (-3) intake. EPA (20:5) ;DHA (22:6) Essential FA Deficiency Rare condition Seen mostly i) Infants and children on low-fat diets ii) People unable to absorb lipids iii) Adults consuming a weight-loss diet consisting of only skim milk Sterols Cholesterol: – Made only by animals, in the liver – Component of cell membrane and myelin – Needed for synthesis of vitamin D, bile, and some hormones Plant sterols phytosterols Correlation of the death rate from CHD with the concentration of plasma cholesterol. The data here obtained from a multiyear study of men with the death rate adjusted for age Response of LDL cholesterol concentrations to an increase in dietary intake The effect of dietary cholesterol on plasma cholesterol is less important than the amount and types of Fas consumed Dietary Fat and Heart Disease 5-28 Saturated Fas with C-chain lengths of 14 (myristic) and 16 (palmitic) are most potent in increasing the plasma choleserol level. Stearic acid (18C – found in many foods including chocolate) has little effect on blood cholesterol Reading Material Introduction to Human Nutrition – Gibney, Vorster and Kok Textbook of Biochemistry – Devlin Nutrition: Science and Applications – Grosvenor & Smolin Biochemistry – Lippincotts Illustrated Reviews: Lippincott , Williams and Wilkins