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Chapter 5: Lipids: Oils, Fats, Phospholipids, and Sterols

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1 Chapter 5: Lipids: Oils, Fats, Phospholipids, and Sterols

LEARNING OBJECTIVES At the end of this chapter, you should be able to: Discuss benefits and risks associated with dietary fats Compare and contrast types of fats Select foods containing healthy fats and limit unhealthy fats

3 THINK 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?

4 Sources of dietary fats
Animal sources: meat, cheese, dairy Plant sources: vegetable oils, nuts, avocados “Hidden” dietary fat: French fries, pizza, pasta dishes, baked goods, salad dressings

5 Visible 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.

6 Role of fats in food Provide texture, flavor, aroma to foods
Provide energy Affect health positively and negatively

7 Canada’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 day the proportion of fat in the Canadian diet has not changed Canadians are now eating less trans fats, less saturated fats, and less cholesterol

8 Fat intake in Canada then and now
a. In the 1970s, a typical dinner included high-fat meat, bread with butter, and mashed potatoes with lots of gravy, and it was usually served with a glass of whole milk. © iStock[ Hernandez b. Today, we drink low-fat milk and eat leaner meats, but we eat more fat from creams, cheese, sauces, and take-out food. © B. o”Kane/Alamy

9 Fat 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 consumption has increased, since our caloric intake has also increased, the proportion of calories from fat in our diet has stayed relatively constant.

10 Types of lipids Lipids: a group of organic molecules, most of which do not dissolve in water Lipids include: Triglycerides: made up of fatty acids and glycerol Fatty acids are chains of carbon atoms with an acid group at one end of the chain They determine the triglyceride’s function in the body Phospholipids: their structure includes a phosphorus atom Sterols: structure composed of multiple rings

11 Triglycerides 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.

12 Triglycerides and fatty acids
The amounts and types of fatty acids in the triglycerides of chocolate allow it to remain brittle at room temperature, snap when bitten into, and then melt quickly and smoothly in your mouth. © Can Stock Photo Inc./ angelsimon Oils are fats that are liquid at room temperature. The properties of the fatty acids in vegetable oil allow it to remain a liquid. ©

13 Triglycerides and fatty acids
Saturated fats: carbon atoms are bonded to as many hydrogen atoms as possible; no carbon to carbon double bonds Plentiful in animal foods, such as meat and dairy products Plant oils are generally low in saturated fatty acids Long-chain saturated fats: implicated in the development of cardiovascular disease associated with increased levels of LDL (“bad”) cholesterol in the blood

14 Triglycerides and fatty acids
Medium-chain saturated fats: behave differently may have more beneficial effects shorter, relatively water-soluble quickly digested and absorbed into the blood stream bypass peripheral fat tissue less likely to be stored as fat

15 Triglycerides and fatty acids
Unsaturated fatty acids: contain one or more carbon-carbon double bonds Monounsaturated fatty acids: one double bond Found in a variety of foods such as meat, olive oil, avocados, and nuts Historically have been thought to be cardioprotective Believed to lower LDL cholesterol More research required to clear health effects

16 Triglycerides and fatty acids
Polyunsaturated fatty acids: more than one double bond Found mainly in plant sources

17 Triglycerides and fatty acids

18 Essential fatty acids Fatty acid composition of food

19 Essential fatty acids Humans are unable to synthesize fatty acids that have double bonds in the omega-6 and omega-3 positions Therefore 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

20 Essential fatty acids Important for the formation of membrane phospholipids, for fertility, red blood cell structure, metabolism, etc. Used to make regulatory proteins called eicosanoids Omega-3 eicosanoids reduce inflammation, lower blood pressure and have other health benefits

21 Essential fatty acids Eating Well with Canada’s Food Guide recommends eating two or more servings of fish per week as a good source of Omega-3 fatty acids Other good sources of Omega-3 fatty acids: walnuts, canola oil, ground flaxseed and many fortified foods

22 Essential fatty acids © Can Stock Photo Inc./Natika
© PSL Images/ Alamy © Don Johnston/ Alamy

23 Trans-fat (trans-fatty acids)
Small amounts occur naturally in dairy products Created when unsaturated fatty acids are partially converted to saturated fatty acids by the industrialized process of hydrogenation Some double bonds converted from cis to trans configuration Decrease the rancidity and increase shelf life Most health endangering dietary fats

24 Trans fatty acids a. 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.

25 Trans fatty acids b. 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.

26 Concept 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?

27 Calculate the trans-fat
A bag of chips has 8 servings and has a trans-fat free label Each 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?

28 Concept check Canadians consume too much saturated fat and too few omega-3 fats. What dietary recommendations could be made to help them improve their diets?

29 Debate the issues Should the government pass additional trans-fat bans? Should unhealthy foods such as soda and potato chips have an additional tax?

30 Phospholipids a. 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.

31 Phospholipids b. Since dietary lipids are hydrophobic (“water-hating”), they cannot dissolve readily in water, making them difficult to transport in water-based environments such as the blood. Phospholipids help suspend lipids in watery environments by acting as emulsifiers. The salad dressing shown here does not contain an emulsifier, so it separates into a layer of oil and vinegar and must be shaken before it is poured on your salad. Ranch salad dressings are emulsified so that they do not separate when left standing. © Can Stock Photo Inc./sadakko

32 Phospholipids c. 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.

33 Sterols Sterols are a type of lipids with distinct ring structures in their chain Cholesterol: sterol made by the liver and consumed in the diet Present in animal cell membranes and in myelin Used to make vitamin D and steroid hormones (e.g., estrogen, testosterone, cortisol) Dietary sources: animal products Plant sterols can reduce human cholesterol One of the leading risk factors for heart disease

34 Cholesterol a. The cholesterol structure shown here illustrates the four interconnected rings of carbon atoms that form the backbone structure that is common to all sterols.

35 Cholesterol b. 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

36 Concept 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?

37 Concept check How are phospholipids and cholesterol similar and different? What is an example of a non-essential nutrient?

38 Digestion and absorption of fat
Mostly in small intestine Bile: 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

39 Digestion and absorption of fat
Micelles: mixture of fatty acids, partially digested triglycerides, cholesterol and bile; facilitate lipid absorption Fat soluble vitamins (A, D, E, and K) are absorbed through the same process

40 Digestion 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)

41 Lipid digestion and absorption

42 Transporting lipids in blood
Lipids are hydrophobic = water fearing (Oil and water don’t mix) Blood is mostly water Lipids are transported in blood by lipoproteins; surrounded by hydrophilic ( = water loving) molecules

43 Chylomicrons Chylomicrons transport triglycerides, cholesterol, phospholipids and fat-soluble vitamins from the small intestine to body cells Triglycerides 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 cells Chylomicron remnants are returned to the liver

44 Lipoproteins (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

45 Very low density lipoproteins (VLDL)
VLDL particles are made in the liver and released to blood VLDL 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

46 Low density lipoproteins (LDL)
LDL particles deliver cholesterol to cells LDL particles bind to LDL receptors on cells to help cholesterol move from the blood into cells High levels of LDL in blood increase risk of heart disease; LDL = “bad” cholesterol

47 High density lipoproteins (HDL)
Reverse cholesterol transport: HDL particles transport cholesterol from cells to the liver; HDL = “good “ cholesterol because it lowers cholesterol content in blood The liver uses cholesterol to make bile

48 LDL vs. HDL LDL particles transport cholesterol from the liver to body cells Try 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 excreted Try to increase your blood levels of HDL (“you want your high to be high”)

49 Lipoproteins are blood transport particles
We do not eat LDL and HDL Dietary lipids (such as cholesterol and triglycerdies) are packaged into lipoprotein particles (such as LDL and HDL) for transport in blood

50 Low density lipoproteins (LDL)

51 Low density lipoproteins (LDL)

52 Improve your lipid profile
Decrease dietary trans-fat, saturated fat, and cholesterol Increase dietary polyunsaturated fats (particularly Omega-3 fatty acids) and monounsaturated fats Quit smoking Exercise Increase dietary fibre

53 Concept check If 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?

54 Checking 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?

55 Concept 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.

56 What are some benefits of lipids/fats discussed so far?
Concept check What are some benefits of lipids/fats discussed so far?

57 Benefits of lipids/fats
Provide texture, flavor, aroma to foods Phospholipids and cholesterol are structural materials of cellular membranes and are starting materials for other molecules Help absorb fat-soluble vitamins Insulate, cushion, lubricate Provide energy

58 Benefits of lipids/fats
Adipose tissue (fat tissue) stores triglycerides that can be broken down for energy production when needed 1 gram of fat = 9 kcal 1 gram or carbohydrates or proteins = 4 kcal Excess calories consumed as carbohydrates or proteins can be converted to fatty acids by the liver and also stored as triglycerides

59 Adipose tissue a. 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

60 Storage 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.

61 Conversion of fatty acids to energy

62 Feasting vs. fasting When 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.

63 Concept check What are benefits and dangers of limiting fat intake?
What are the dangers of consuming too much fat?

64 Lipids and disease The amount and type of fat you eat can affect your health Too little dietary fats can affect growth, sight and impair many physiological functions Too much dietary fats can increase total calorie intake and lead to weight gain Too much of trans fats and saturated fats can contribute to cardiovascular disease and cancer

65 Atherosclerosis Atherosclerosis: 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 oxidization Atherosclerotic plaques can narrow blood vessels and limit blood flow so that less oxygen and fewer nutrient molecules are delivered to tissues

66 Development of atherosclerosis

67 Development of atherosclerosis

68 Atherosclerosis can lead to heart attacks and strokes
Atherosclerotic plaques can rupture and stimulate clot formation in blood vessels to completely block blood flow In 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)

69 Risk factors for atherosclerosis and cardiovascular disease
High blood pressure (hypertension) Obesity Diabetes mellitus Smoking Blood lipids (high LDL, triglycerides; low HDL) Diet Sedentary lifestyle Family history, age, gender, race

70 Risk factors for cardiovascular disease

71 Diet and heart disease risk
Diets that prevent heart disease: High in fibre, antioxidants and B vitamins Examples: fruits, vegetables, nuts, whole grains and fish

72 Diet and heart disease risk
Diets that contribute to heart disease: High in trans fats, saturated fats and sodium Examples: red meat, processed meats, hydrogenated vegetable oils Health Canada was the first government in the world to implement the mandatory labeling of trans fats on prepackaged foods

73 Mediterranean diet pyramid
Cardio-protective effects of the traditional Mediterranean and Asian diets versus modern diets a. 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.

74 Traditional 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.

75 Eating to reduce the risk of heart disease
© Can Stock Photo Inc./ oksix © Can Stock Photo Inc./dimol

76 Eating to reduce the risk of heart disease
© Can Stock Photo Inc./BVDC © Can Stock Photo Inc. ./ ildi

77 Cholesterol and saturated fats in foods

78 Dietary 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 acids low in trans fats (more studies needed to determine the association between trans fats and some cancers)

79 Dietary fat and obesity
Excess dietary fat intake contributes to weight gain However, fat content in the diet is not the sole reason for high rate of obesity in Canada Weight gain occurs when energy intake exceeds energy expenditure regardless whether extra energy comes from fat, carbohydrate, or protein

80 Concept check What are some benefits of diets rich in fruits and vegetables? What are some consequences of diets high in animal fats?

81 Concept check Which dietary and lifestyle changes can you make to decrease your risk of atherosclerosis and cardiovascular disease?

82 Dietary lipid recommendations
The dietary reference intake (DRIs): Total fat: 20%–35% of total calories 30–40% for ages 1–3 & 25–35% for ages 3–18 Adequate intake for linoleic acid = 12 g per day for women and 17 g per day for men Adequate intake for alpha linolenic acid = 1.1.g per day for women and 1.6 g per day for men Cholesterol, saturated fat, and trans fats: keep intake to minimum

83 Making wise food choices
Canada’s Food Guide, the section “Make Each Food Serving Count” recommends choosing lower fat options in all food groups Examples: smart fat choices from meat and meat alternatives, milk and milk alternatives groups

84 Making wise food choices
Canadian Food Guide recommends making wise fat choices

85 Food 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

86 COPYRIGHT Copyright © 2014 John Wiley & Sons Canada, Ltd. All rights reserved. Reproduction or translation of this work beyond that permitted by Access Copyright (The Canadian Copyright Licensing Agency) is unlawful. Requests for further information should be addressed to the Permissions Department, John Wiley & Sons Canada, Ltd. The purchaser may make back-up copies for his or her own use only and not for distribution or resale. The author and the publisher assume no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information contained herein.

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