Presentation on theme: "Chapter 5: Lipids: Oils, Fats, Phospholipids, and Sterols"— Presentation transcript:
1Chapter 5: Lipids: Oils, Fats, Phospholipids, and Sterols
2CHAPTER 5: LIPIDS: OILS, FATS, PHOSPHOLIPIDS, AND STEROLS LEARNING OBJECTIVESAt the end of this chapter, you should be able to:Discuss benefits and risks associated with dietary fatsCompare and contrast types of fatsSelect foods containing healthy fats and limit unhealthy fats
3THINK about this – then share within a PAIR – then SHARE with the class Which foods in your diet provide fat?Why do you need fat in your diet?What are the benefits and consequences of a low-fat diet?
4Sources of dietary fats Animal sources: meat, cheese, dairyPlant sources: vegetable oils, nuts, avocados“Hidden” dietary fat: French fries, pizza, pasta dishes, baked goods, salad dressings
5Visible and hidden fats The amount of fat in a food is not always obvious. The two strips of bacon in this breakfast provide a total of 8 g of fat, and the muffin provides 16 g.
6Role of fats in food Provide texture, flavor, aroma to foods Provide energyAffect health positively and negatively
7Canada’s changing fat intake According to Statistics Canada, the following changes have been observed between 1981 and 2009:average fat intake has risen from 85 grams per day to 91 grams per daythe proportion of fat in the Canadian diet has not changedCanadians are now eating less trans fats, less saturated fats, and less cholesterol
9Fat intake in Canada then and now c. In 1981, it is estimated that Canadians consumed an average of 2,214 kilocalories and 85 grams of fat per day. This rose to 2,358 kilocalories and 91 grams of fat in While our total fat consumptionhas increased, since our caloric intake has also increased, the proportion of calories from fat in our diet has stayed relatively constant.
10Types of lipidsLipids: a group of organic molecules, most of which do not dissolve in waterLipids include:Triglycerides: made up of fatty acids and glycerolFatty acids are chains of carbon atoms with an acid group at one end of the chainThey determine the triglyceride’s function in the bodyPhospholipids: their structure includes a phosphorus atomSterols: structure composed of multiple rings
11Triglycerides and fatty acids a. A triglyceride contains glycerol and three fatty acids. The carbon chains of the fatty acids vary in length from short-chain fatty acids (4 to 7 carbons) to medium-chain (8 to 12 carbons) and long-chain fatty acids (more than 12 carbons). The types of fatty acids in triglycerides determine their texture, taste, physical characteristics, and actions in the body.
13Triglycerides and fatty acids Saturated fats: carbon atoms are bonded to as many hydrogen atoms as possible; no carbon to carbon double bondsPlentiful in animal foods, such as meat and dairy productsPlant oils are generally low in saturated fatty acidsLong-chain saturated fats:implicated in the development of cardiovascular diseaseassociated with increased levels of LDL (“bad”) cholesterol in the blood
14Triglycerides and fatty acids Medium-chain saturated fats:behave differentlymay have more beneficial effectsshorter, relatively water-solublequickly digested and absorbed into the blood streambypass peripheral fat tissueless likely to be stored as fat
15Triglycerides and fatty acids Unsaturated fatty acids: contain one or more carbon-carbon double bondsMonounsaturated fatty acids: one double bondFound in a variety of foods such as meat, olive oil, avocados, and nutsHistorically have been thought to be cardioprotectiveBelieved to lower LDL cholesterolMore research required to clear health effects
16Triglycerides and fatty acids Polyunsaturated fatty acids: more than one double bondFound mainly in plant sources
18Essential fatty acidsFatty acid composition of food
19Essential fatty acidsHumans are unable to synthesize fatty acids that have double bonds in the omega-6 and omega-3 positionsTherefore linoleic acid (LA) (omega-6) and alpha-linolenic acid (ALA) (omega-3) are considered essential fatty acids (EFAs) and must be consumed in the diet
20Essential fatty acidsImportant for the formation of membrane phospholipids, for fertility, red blood cell structure, metabolism, etc.Used to make regulatory proteins called eicosanoidsOmega-3 eicosanoids reduce inflammation, lower blood pressure and have other health benefits
21Essential fatty acidsEating Well with Canada’s Food Guide recommends eating two or more servings of fish per week as a good source of Omega-3 fatty acidsOther good sources of Omega-3 fatty acids: walnuts, canola oil, ground flaxseed and many fortified foods
23Trans-fat (trans-fatty acids) Small amounts occur naturally in dairy productsCreated when unsaturated fatty acids are partially converted to saturated fatty acids by the industrialized process of hydrogenationSome double bonds converted from cis to trans configurationDecrease the rancidity and increase shelf lifeMost health endangering dietary fats
24Trans fatty acidsa. The orientation of hydrogen atoms around the double bond distinguishes cis fatty acids from trans fatty acids. Most unsaturated fatty acids found in nature have double bonds in the cis configuration.
25Trans fatty acidsb. Small amounts of trans fatty acids occur naturally, and larger amounts are generated by hydrogenation. In 2007, Health Canada called on food manufacturers to voluntarily reduce the amount of trans fat in their products to less than 5% of total fat, which the majority of manufacturers have now complied with.
26Concept check What are similarities and differences between: saturated and unsaturated fats?monounsaturated and polyunsaturated fats?omega-3 and omega-6 fats?cis-fats and trans-fats?
27Calculate the trans-fat A bag of chips has 8 servings and has a trans-fat free labelEach serving has 0.4 g of trans fat (label lists as 0 g of fat)If you eat ½ of the bag of chips, how many grams of trans-fat have you consumed?
28Concept checkCanadians consume too much saturated fat and too few omega-3 fats. What dietary recommendations could be made to help them improve their diets?
29Debate the issuesShould the government pass additional trans-fat bans?Should unhealthy foods such as soda and potato chips have an additional tax?
30Phospholipidsa. Like a triglyceride, a phospholipid has a backbone of glycerol, but it contains two fatty acids rather than three. Instead of the third fatty acid, a phospholipid has a chemical group containing phosphorus, called a phosphate group. The fatty acids at one end of a phospholipid molecule are hydrophobic: insoluble in water, but soluble in fat; whereas the phosphate-containing region at the other end is hydrophilic: soluble in water, but insoluble in fat.
32Phospholipidsc. Phospholipids are an important component of cell membranes.They form a double-layered sheet called the lipid bilayer by orienting the hydrophilic,phosphate-containing “heads” toward the aqueous (water) environments inside and outside the cell and the hydrophobic fatty acid “tails” toward each other to form the lipid centre of the membrane. The lipid bilayer is a critical component of the cell, as it limits what substances can easily move into and out of it.
33SterolsSterols are a type of lipids with distinct ring structures in their chainCholesterol: sterol made by the liver and consumed in the dietPresent in animal cell membranes and in myelinUsed to make vitamin D and steroid hormones (e.g., estrogen, testosterone, cortisol)Dietary sources: animal productsPlant sterols can reduce human cholesterolOne of the leading risk factors for heart disease
34Cholesterola. The cholesterol structure shown here illustrates the four interconnected rings of carbon atoms that form the backbone structure that is common to all sterols.
35Cholesterolb. Egg yolks and organ meats such as liver and kidney are high in cholesterol. Lean red meats and skinless chicken are low in total fat but still contain some cholesterol. Cholesterol is not found in plant cell membranes, so even high-fat plant foods, such as nuts, peanut butter, and vegetable oils, do not contain cholesterol
36Concept check Where are most phospholipids found in the body? Why is cholesterol not a dietary essential?Which is higher in cholesterol: a 15-mL spoonful of peanut butter or an egg?
37Concept checkHow are phospholipids and cholesterol similar and different?What is an example of a non-essential nutrient?
38Digestion and absorption of fat Mostly in small intestineBile: acts as an emulsifier breaking down larger lipid droplets into smaller ones making them more accessible to lipase (lipid digesting enzyme)Bile is stored in the gall bladder before entering the small intestine
39Digestion and absorption of fat Micelles: mixture of fatty acids, partially digested triglycerides, cholesterol and bile; facilitate lipid absorptionFat soluble vitamins (A, D, E, and K) are absorbed through the same process
40Digestion and absorption of fat Dietary fibre binds cholesterol to keep it from being reabsorbed into the body from the small intestine (so more is excreted from the body)
42Transporting lipids in blood Lipids are hydrophobic = water fearing(Oil and water don’t mix)Blood is mostly waterLipids are transported in blood by lipoproteins; surrounded by hydrophilic ( = water loving) molecules
43ChylomicronsChylomicrons transport triglycerides, cholesterol, phospholipids and fat-soluble vitamins from the small intestine to body cellsTriglycerides in chylomicrons are broken down into glycerol and fatty acids by lipoprotein lipase (in blood vessels) to cross membranes then are reassembled into triglycerides in cellsChylomicron remnants are returned to the liver
44Lipoproteins (examples: LDL & HDL) Lipoproteins consist of a core of triglycerides and cholesterol surrounded by a shell of protein, phospholipids, and cholesterol.Phospholipids orient with their fat-soluble “tails” toward the interior of the lipoprotein and their water-soluble “heads” toward the watery environment outside the lipoprotein
45Very low density lipoproteins (VLDL) VLDL particles are made in the liver and released to bloodVLDL function similar to chylomicrons (transport triglycerides which are broken down by lipoprotein lipase)Remainder of VLDL particles is either returned to the liver or made into LDL particles
46Low density lipoproteins (LDL) LDL particles deliver cholesterol to cellsLDL particles bind to LDL receptors on cells to help cholesterol move from the blood into cellsHigh levels of LDL in blood increase risk of heart disease; LDL = “bad” cholesterol
47High density lipoproteins (HDL) Reverse cholesterol transport: HDL particles transport cholesterol from cells to the liver; HDL = “good “ cholesterol because it lowers cholesterol content in bloodThe liver uses cholesterol to make bile
48LDL vs. HDLLDL particles transport cholesterol from the liver to body cellsTry to decrease your blood levels of LDL(“you want your low to be low”)HDL particles transport cholesterol from body cells to the liver so they can be excretedTry to increase your blood levels of HDL(“you want your high to be high”)
49Lipoproteins are blood transport particles We do not eat LDL and HDLDietary lipids (such as cholesterol and triglycerdies) are packaged into lipoprotein particles (such as LDL and HDL) for transport in blood
52Improve your lipid profile Decrease dietary trans-fat, saturated fat, and cholesterolIncrease dietary polyunsaturated fats (particularly Omega-3 fatty acids) and monounsaturated fatsQuit smokingExerciseIncrease dietary fibre
53Concept checkIf a person does not have LDL receptors, what would you expect to happen to blood levels of LDL?What are examples of foods you can limit and increase to lower your LDL and raise your HDL?
54Checking student learning outcomes What are the benefits and risks of dietary fats?How are fats classified? What are the similarities and differences between types of fat?Which foods should be consumed and avoided to improve health?
55Concept check Which of the following is true? Cholesterol is made in the small intestine.Bile is packaged into HDL particles.HDL is oxidized during atherosclerosis.LDL delivers cholesterol to cells.
56What are some benefits of lipids/fats discussed so far? Concept checkWhat are some benefits of lipids/fats discussed so far?
57Benefits of lipids/fats Provide texture, flavor, aroma to foodsPhospholipids and cholesterol are structural materials of cellular membranes and are starting materials for other moleculesHelp absorb fat-soluble vitaminsInsulate, cushion, lubricateProvide energy
58Benefits of lipids/fats Adipose tissue (fat tissue) stores triglycerides that can be broken down for energy production when needed1 gram of fat = 9 kcal1 gram or carbohydrates or proteins = 4 kcalExcess calories consumed as carbohydrates or proteins can be converted to fatty acids by the liver and also stored as triglycerides
59Adipose tissuea. Adipose tissue is an important source of stored energy. It also insulates the body from changes in temperature and provides a cushion to protect against shock. The amount and location of adipose tissue affect our physical appearance, specifically our body size and shape. This tissue is preferentially deposited in some body areas, such as your abdominal region, rather than other areas, such as your thighs and shoulders. Where adipose tissue is stored varies across both male and female populations and is based almost entirely on individual genetics. Thus, a specific diet or exercise regime cannot honestly promise results for fat loss from one specific location over another
60Storage of excess fatty acids b. Adipose tissue cells contain large droplets of triglyceride that push the other cell components to the perimeter of the cell. As weight is gained, the triglyceride droplets enlarge and, once they reach their maximum size, they divide, forming new adipocytes, or fat cells. When weight is lost and total body fat is lowered, fat cells can only shrink, not disappear. Once fat cells have been added to the body, they remain, making it more difficult to achieve the pre-fat gain state and appearance.
62Feasting vs. fastingWhen we consume too many calories, excess energy is stored in the form of triglycerides. When the energy needs of our body are insufficient to fuel body processes and physical activity, triglycerides in adipose tissue are broken down, releasing fatty acids, which can be used to provide energy.
63Concept check What are benefits and dangers of limiting fat intake? What are the dangers of consuming too much fat?
64Lipids and diseaseThe amount and type of fat you eat can affect your healthToo little dietary fats can affect growth, sight and impair many physiological functionsToo much dietary fats can increase total calorie intake and lead to weight gainToo much of trans fats and saturated fats can contribute to cardiovascular disease and cancer
65AtherosclerosisAtherosclerosis: a type of cardiovascular disease that involves buildup of fatty material in the artery walls (atherosclerotic plaques)Atherosclerotic plaques generation occurs following blood vessel injury, inflammation and LDL cholesterol oxidizationAtherosclerotic plaques can narrow blood vessels and limit blood flow so that less oxygen and fewer nutrient molecules are delivered to tissues
68Atherosclerosis can lead to heart attacks and strokes Atherosclerotic plaques can rupture and stimulate clot formation in blood vessels to completely block blood flowIn the heart, this causes heart attacks (also called myocardial infarctions, or MIs)In the brain, this causes strokes (also called cerebral vascular accidents, or CVAs)
69Risk factors for atherosclerosis and cardiovascular disease High blood pressure (hypertension)ObesityDiabetes mellitusSmokingBlood lipids (high LDL, triglycerides; low HDL)DietSedentary lifestyleFamily history, age, gender, race
71Diet and heart disease risk Diets that prevent heart disease:High in fibre, antioxidants and B vitaminsExamples: fruits, vegetables, nuts, whole grains and fish
72Diet and heart disease risk Diets that contribute to heart disease:High in trans fats, saturated fats and sodiumExamples: red meat, processed meats, hydrogenated vegetable oilsHealth Canada was the first government in the world to implement the mandatory labeling of trans fats on prepackaged foods
73Mediterranean diet pyramid Cardio-protective effects of the traditional Mediterranean and Asian diets versus modern dietsa. In the Mediterranean region, the main source of dietary fat is olive oil, and the typical diet is high in nuts, vegetables, and fruits. Fish is consumed routinely and red meat, rarely. Despite a fat intake that is similar to that of the Canadian diet, the incidence of heart disease is much lower. This diet pyramid is based on the dietary patterns of Crete, Greece, and southern Italy around 1960, when the rates of chronic disease in this region were among the lowest in the world.
74Traditional Asian diet pyramid b. In Asian countries, plant foods that are rich in fibre and antioxidants form the base of the diet, and animal products are more peripheral. Traditional Asian diets include more fish and seafood than red meat.Combined with small amounts of vegetable oil, this pattern produces a balance of omega-3 to omega-6 fatty acids that helps prevent heart disease.* Routine consumption of green tea, which is high in antioxidants, may also contribute to the low rate of chronic disease in the region.* This diet pyramid was inspired by the traditional cuisines of southern and eastern Asia.
78Dietary fat and cancer Cancer is a leading cause of death in Canada Research indicates that the risk of cancer may be decreased by choosing diets:high in fruits, vegetables, antioxidants and omega-3 fatty acidslow in trans fats (more studies needed to determine the association between trans fats and some cancers)
79Dietary fat and obesity Excess dietary fat intake contributes to weight gainHowever, fat content in the diet is not the sole reason for high rate of obesity in CanadaWeight gain occurs when energy intake exceeds energy expenditure regardless whether extra energy comes from fat, carbohydrate, or protein
80Concept checkWhat are some benefits of diets rich in fruits and vegetables?What are some consequences of diets high in animal fats?
81Concept checkWhich dietary and lifestyle changes can you make to decrease your risk of atherosclerosis and cardiovascular disease?
82Dietary lipid recommendations The dietary reference intake (DRIs):Total fat: 20%–35% of total calories30–40% for ages 1–3 & 25–35% for ages 3–18Adequate intake for linoleic acid = 12 g per day for women and 17 g per day for menAdequate intake for alpha linolenic acid = 1.1.g per day for women and 1.6 g per day for menCholesterol, saturated fat, and trans fats: keep intake to minimum
83Making wise food choices Canada’s Food Guide, the section “Make Each Food Serving Count” recommends choosing lower fat options in all food groupsExamples: smart fat choices from meat and meat alternatives, milk and milk alternatives groups
85Food labels Pay attention to the Nutrition Facts panel Be careful when choosing the lower-fat content food products; some of them may have reduced nutritional value and may have negative health implications