Human Nutrition Chapter 5

Human Nutrition - 03.02.2020 Chapter 5   Lipids: soluble in organic solvents but not in water (and our body is mostly water) o The usefulness of fats in food and fats in the body (Table 5-1) o Major energy storage o 9 calories per gram o Key form of stored energy o Muscle fuel as well as emergency fuel supple in times of illness or diminished food intake o Insulation o Cell membranes o Raw materials o Nutrients, energy, transport (of fat soluble vitamins A, D, E, K), raw materials, sensory appeal, appetite, satiety and texture of foods Recommendations for dietary fat: o Nutrition recommendations for Canadians (NRC): <30% energy from dietary fat o o o  Fat: Polyunsaturated fatty acids - DRI  5-10% energy from omega-6  06-1.2% energy from omega-3 o Cholesterol:  DRI: minimize intake within context of healthy diet  about 1/3 population responds to lowering dietary cholesterol intake: limit eggs, shellfish, liver etc. but these are nutritious foods Lipid classification: o Triglycerides  95% of lipid in foods and body fat  3 fatty acids and glycerol backbone  Glycerol is made from glucose or amino acids  Fatty acids are classified by:  Chain length  Short (10+ carbons)  Medium (12-14 carbons)  Long (16+ carbons)  Degree of saturation (double bonds C=C)  Saturated: no double bonds  Tend to be solid at room temp.  Butter fat, coconut, and palm oils  Monounsaturated: 1 double bond  Canola and olive oils  Polyunsaturated: 2+ double bonds  Tend to be liquid (oils) at room temp.  Effects of processing unsaturated fats  Margarine:  Hydrogenation: removing C=C double bonds by adding hydrogen o  DRI: 20-35% energy from dietary fat NRC: <10% energy from saturated fat WHO: <1% energy from trans fat  Low saturated and trans fat intake helps to reduce blood cholesterol and thus heart disease  Unsaturated fat reduces blood clotting Vegetable oil — hard margarine, hydrogenated shortening  Better storage, less rancidity and high smoke point for frying  Creates trans-fatty acid which act like saturated fatty acids in the body (increases risk of cardiovascular disease) Trans fatty acids  Food labels require a separate category   Consumed in processed foods, fast food, baked goods, potato chips Bonding different oils to produce a soft margarine  E.g. Becel and other non-hydrogenated products   Phospholipids  Glycerol backbone + 2 fatty acids + phosphorus containing molecule  Water and fat soluble  Can serve as emulsifier  E.g. lecithin in egg yolk, no special health promoting abilities o Sterols  Cholesterol: present in all cell membranes, bile and precursor for:  Vitamine D  Sex hormones (estrogen and testosterone)  Stress hormones (e.g. epinephrine) Lipid Digestion and Absorption: o In the stomach:  Fat separates from watery components and floats to top  Little fat digestion o In the small intestine:  Bile needed to emulsify lipid and chyme  Pancreatic lipase (enzyme) to split into smaller particles o Small lipids: short and medium chain fatty acids and glycerol  Enter capillary network — bloodstream o Large lipids: long chain fatty acids and monoglycerides (glycerol +1 fatty acid) travel in bloodstream as chylomicrons Lipid Transport: o Lipoproteins:  Chylomicrons: dietary lipid and carrier proteins — transport fats through watery blood fluids  Very low density lipoprotein (VLDL): triglycerides synthesized in liver — body cells  Low density lipoprotein (LDL): triglycerides and cholesterol circulating in blood — body cells  High density lipoprotein (HDL): excess cholesterol in body cells — liver for excretion Lipid metabolism: o When body starts to run out of fuel from food, turns to body stores o Fatty acids are used for energy by many organs: typical fuel mix is 50/50 carbohydrate/lipid for liver and muscle at rest o Any time fat broken down for energy CHO must be available  Otherwise, ketones develop (products of incomplete fat breakdown) and build up in blood and urine o     Blood Cholesterol and Cardiovascular Disease Risk: o High LDL cholesterol increases risk for heart disease  Major risk factors for heart disease  High LDL cholesterol Low HDL cholesterol A diet high in satiated and trans fats and low in vegetables, fruits and whole grains  Diet and lifestyle factors important o Cholesterol has precursor and structural roles: required for health  74%-80% is synthesized in the body  Drugs to inhibit synthesis  Stimulation of synthesis by saturated fats  Dietary cholesterol plays a lesser role than saturated and trans fat in cardiovascular disease  ~60% exhibit little increase in blood cholesterol with high cholesterol diet Essential fatty acids: o linoleic acids and linolenic acid (omega-6 and omega-3)  The only fatty acids that cannot be synthesized by the body  Essential nutrients  Polyunsaturated fatty acids  Used by the body to make eicosanoids  Biologically active compounds that regulate body functions  When diet deficient in all polyunsaturated fatty acids (PUFAs)  Skin lesions  Reproductive failure  Fatty lvier  Kidney disorders  Reduced learning and growth  Impaired vision  Deficiency is rare, as the body stores some extra o Omega-6: C=C 6 carbons from end  Ex: linoleic acid  DRI: 5-10% energy from n-6 fatty acids  Food sources: vegetable oils, seeds, nuts, whole grain products o Omega-3  C=C 3 carbons from end  DRI: 06-1.2% energy from n-3 fatty acids  Food sources: flaxseed, flaxseed oil, canola oil, fish (especially deep sea fish)  Three main types:  ALA - from plant sources  EPA - from fish sources  DHA - from fish sources  Body can retro-convert some ALA to EPA/DHA o Need more n-3 in our diet to prevent heart disease  Recommendation: 2-3 meals of fatty fish per week to improve heart health  EPA/DHA content reduced in fried fish  Studies show that fish more beneficial than supplements o Potential benefits of EPA/DHA  Heart disease (supported by most studies)    Infant growth and development (strong evidence) Cancer (research promising, but need further evidence) Mercury in Fish: o Contaminated fish:  Generally low levels of mercury contaminate most fish species  It is yet to be established just how much mercury worsens preexisting heart disease o Fish heavily contaminated with mercury  Shark  Swordfish  King mackerel  Fresh tuna steak (Albacore)  Tilefish o Fish/seafood lower in mercury  Shrimp  Canned tuna light  Canned albacore (white) tuna contains more mercury than light tuna  Salmon  Pollock  Catfish o Recommendations:  Consume a variety of fish  Minimizes exposure to any particular toxin that may accumulate in a particular species  Pregnant women and children  Most sensitive to the side effects of mercury  Can safely benefit from safer fish varieties with recommended limits Major Dietary Sources of Fat o Dairy products (excluding milk and butter) o Processed meat o Margarine o Salad and cooking oils o Bakery products o Fresh meats o butter o Fluid milk o All except salad and cooking oils are sources of saturated fat Consumer Corner: fat replacers o Fat replacement  Alter preparation method for example  Add water or whip air into foods  Add non fat milk to creamy foods  Use lean products vs high fat  Bake rather than fry      Fat replacers can be CHO, fibre, fat or protein based Olestra (core of sucrose and 8 fatty acids)  Not digested or absorbed (non caloric)  Not approved Canada  Approved for snack foods in USA  Concerns: digestive problems, losses of nutrients and phytochemical Controversy 5: Is butter really back? o Lots of consumer advice in the public media that is often controversial o Goals: prevention of cardiovascular diseases o Strong scientific evidence for diet low in saturated fat o Historic guidelines:  Cut total fat intake for cardiovascular prevention  However, replacement of fats with sugars lead to negative health outcome  E/g/ increased diabetes and CVD  Guidelines evolved with new evidence o Milestone Research:  Seven countries study of healthy people  Death rates from heart disease were strongly associated with diets high in saturated fats  Death rates from heart disease were only weakly associated with diets high in total fat  Finland and the Greek island of Crete were the two countries with the highest fat intake  Finland had the highest rate of death from heart disease  Crete had the lowest rate of death for heart disease  Relative to Finnish people, people in Crete had a died high in olive oil and low in saturated fat o Present Guidelines:  Replace saturated fats with unsaturated fats  Specifically polyunsaturated fats are effective  Avoid trans fat  When replacing saturated fats with polyunsaturated  Every 1% reduction in calories from saturated fatty acids — 2-3% reduction in CVD Health Canada Approved Health Claim: o Replacing saturated fats with polyunsaturated and monounsaturated fats (from vegetables oils) helps lower/reduce cholesterol o Debate lies in the fact that the biological mechanism underlying he beneficial effects are unknown  Role of genetic background unknown  Actions of specific fatty acids undetermined  Some saturated fats might not be detrimental  Oversupply of some polyunsaturated fats might be detrimental o Controversy on butter: saturated fatty acids  Meta-analysis:     Failed to correlated dietary saturated fat intake with the prevention of cardiovascular dieases  Heavily criticized analysis  Design limitations became apparent Beneficial portfolio diets emerged:  A healthy vegetarian diet  A healthy American/Canadian style diet  The classic Mediterranean diet  o