NR228 Nutrition
Chapter 5
Fats
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List the major functions of triglyceride in food and physiologically in the body.
State the functions of phospholipids and cholesterol.
Summarize the structures and sources of the three types of lipids.
Discuss the function and sources of the linolenic and linoleic essential fatty acids.
Learning Objectives (1 of 2)
Explain the digestion, absorption, and transportation of lipids in the body.
Identify the three different types of lipoproteins and their functions.
Describe the potential health concerns related to dietary fat intake.
Learning Objectives (2 of 2)
Lipids comprise triglycerides, phospholipids, and sterols.
Of the fat in foods and in the body, 95% is triglycerides.
Fat is valuable and necessary for health.
Role in Wellness
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Source of energy
Palatability
Satiety and satiation
Food processing
Nutrient source
Contain or transport fat-soluble vitamins A, D, E, K.
Contain or transport essential fatty acids.
Food Functions: Triglycerides
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Skin lesions and scaliness (eczema)
Cause: increased permeability leading to breakdown of membranes throughout the body
Increased susceptibility to infections
Patients at risk
Older patients with peripheral vascular disease
Patients with fat malabsorption
Patients receiving treatment for protein malnutrition
Patients recovering from serious burns and accidents
Essential Fatty Acid Deficiency
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Stored energy
Adipose tissue storage form of fat (mainly triglycerides)
Important source of fuel during illness and food restriction, and major energy source for muscle work
Organ protection
Temperature regulator
Insulation
Physiologic Functions: Triglycerides
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Functions of phospholipids
Cell membrane structure
Lecithin: main phospholipid, part of lipoproteins
Functions of sterols
Precursors to bile, vitamin D, sex hormones, cells in brain and central nervous system
Cholesterol: part of cell membranes, nerve tissue, and hormones
Liver: synthesizes cholesterol to produce bile
Functions of Phospholipids and Sterols
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Triglycerides
Largest class of lipids in body and foods
Composed of glycerol and three fatty acids
Fatty acids:
Saturated fatty acids
Monounsaturated fatty acids
Polyunsaturated fatty acids
Structure and Sources of Lipids: Saturated and Unsaturated Fats
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Structure and Sources of Lipids: Structure and Sources
Fig. 5.2 Formation and structure of a triglyceride.
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Structure and Sources of Lipids: Process of Hydrogenation
Fig. 5.3 Process of hydrogenation.
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Triglycerides
Monounsaturated fatty acid
Primary sources include olive oil, peanuts (peanuts and peanut oil), avocado, and canola oil.
Polyunsaturated fatty acid (PUFA)
Sources: vegetable oils (corn, safflower, wheat germ, canola, sesame, and sunflower), fish, and margarine
Omega-3 fatty acids (linoleic acid), eicosapentaenoic acid (EPA)
Omega-6 fatty acids (linoleic acid)
Food sources of omega-3 fatty acids and supplements
Structure and Sources of Lipids: Saturated and Unsaturated Fats
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Structure and Sources of Lipids: Dietary Fat Contents (1 of 2)
Fig. 5.4 Comparison of dietary fats in terms of cholesterol, saturated fat, and the most common unsaturated fats.
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Structure and Sources of Lipids: Dietary Fat Contents (2 of 2)
Fig. 5.5 Examples of fatty acids found in foods. Foods with these fatty acids include: A, animal-derived foods (beef, poultry, lamb, pork, eggs, dairy, and tropical oils); B, olive oil, peanuts (butter and oil), and canola oil; C, vegetable oils (margarine and salad dressings), some animal fats, and prepared foods; and D, fatter fish (bluefish, tuna, salmon, etc.), fish, and canola oil.
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There are differences in structure between phospholipids and triglycerides.
Body manufactures phospholipids; therefore, they are not essential nutrients.
Lecithin, the main body phospholipid, functions as an emulsifier.
Structure and Sources of Lipids: Phospholipids
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Structure and Sources of Lipids: A Phospholipid: Lecithin
Fig. 5.6 A phospholipid: lecithin.
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Sterol structures are carbon rings intermeshed with side chains of carbon, hydrogen, and oxygen.
They are synthesized by the body and therefore are not essential nutrients.
One type of sterol is cholesterol:
Dietary cholesterol: 25% of body cholesterol; rest provided by liver synthesis.
Contained only in animal-derived foods.
Structure and Sources of Lipids: Sterols
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Structure and Sources of Lipids: A Sterol: Cholesterol
Fig. 5.7 A sterol: cholesterol. Foods containing cholesterol include animal-derived foods such as beef, pork, chicken, bacon, luncheon meats, eggs, fish, and dairy products.
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Mouth
Primary fat digestive process is mechanical, inasmuch as teeth masticate fatty food.
Glands of the tongue produce fat-splitting enzyme (lingual lipase), released with saliva.
Stomach
Mechanical digestion continues through peristalsis.
Fat-splitting enzymes such as gastric lipase hydrolyze fatty acids from triglycerides.
Fat as a Nutrient in the Body: Digestion (1 of 2)
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Small intestine
Duodenum releases hormone cholecystokinin (CCK).
CCK action causes gallbladder to release bile into small intestine.
Muscular action continues digestion.
Pancreatic enzyme, lipase, breaks down triglycerides.
Some fats may pass through undigested and are excreted.
Fat as a Nutrient in the Body: Digestion (2 of 2)
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Bile salts assist movement of lipids to villi.
Fatty acids and glycerol re-form triglycerides once through the cell wall.
Triglycerides form into chylomicrons, transported through lymphatic system to circulatory system.
Fat as a Nutrient in the Body: Absorption (1 of 2)
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Some glycerol and short- and medium-chain fatty acids (MCTs) are absorbed directly into capillaries leading to portal vein and liver.
Lipoprotein lipase in the blood breaks down triglycerides in the chylomicrons into free fatty acids and glycerol.
Muscle and adipose cells use fatty acids for energy or re-form them into triglycerides that are stored as energy.
Fat as a Nutrient in the Body: Absorption (2 of 2)
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Catabolism and anabolism
Catabolism (breakdown) of lipids for energy
Acetyl coenzyme A
Tricarboxylic acid (TCA) cycle
Adenosine triphosphate (ATP)
Ketone bodies/ketosis
Anabolism (synthesis) of lipids, or lipogenesis
Regulatory hormones
Fat as a Nutrient in the Body: Metabolism
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Summary of Fat Digestion and Absorption
Fig. 5.8 Summary of fat digestion and absorption. CCK, Cholecystokinin. (From Rolin Graphics.)
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High-fat foods = high-calorie foods.
DRIs based on AMDRs recommend 20% to 30% of kilocalories from fats, with 10% or more of kilocalories from saturated fats.
Total fat intake for average daily kcal intake of 2000 to 2500 kcal should range
Total fat: ≤40 to 97 g (400 to 875 kcal) per day
Saturated fat: ≤25 to 20 g (225 to 180 kcal) per day
For children younger than 5 years of age: at least 20% of kilocalories as fat
MyPlate emphasizes oils from fish and plants.
Fat Intake and Issues: Fat Content of Foods
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Visible versus invisible fat in foods
General characteristics of fat content:
Cooking method
How food is eaten
Whether food source is animal or plant derived
Availability of healthy menu choices for dining out
Lower-fat cultural and ethnic cuisine
Fat Intake and Issues: Detecting Dietary Fat
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Trends in the fast-food marketplace
How to reduce fat and still have quick meals
Family eating habits
Programs and classes
Mixing low-fat and high-fat foods
Fat Intake and Issues: Fast, But High-Fat, Food
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Hydrogenated and emulsified fats and oils
Oxidation of unsaturated fats
Hydrogenation makes fat more solid and stable
Cis and trans fatty acids
Relationship of trans fatty acids to elevated cholesterol levels
Trans fatty acid content mandatory on food labels
Preserving Fats in Foods (1 of 3)
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Preserving Fats in Food (2 of 3)
Fig. 5.9 Cis bond to trans bonds.
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Antioxidants
Natural: vitamin C (ascorbic acid), vitamin E (tocopherol)
Synthetic: butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT)
Preserving Fats in Foods (3 of 3)
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Sources of dietary cholesterol
Sources of blood cholesterol
High blood cholesterol level associated with high risk for coronary vascular disease
Food Cholesterol versus Blood Cholesterol (1 of 5)
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Lipoproteins
Chylomicrons
Very low-density lipoproteins (VLDLs)
Low-density lipoproteins (LDLs)
High-density lipoproteins (HDLs)
Plaque formation
High LDL level increases risk for coronary artery disease; high HDL decreases risk
Total blood cholesterol = LDL + HDL
Food Cholesterol versus Blood Cholesterol (2 of 5)
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Food Cholesterol versus Blood Cholesterol (3 of 5)
Fig. 5.10 Lipoprotein.
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Blood Cholesterol Levels
Risk Classification Total Cholesterol LDL Cholesterol
Desirable <200 mg/dL <130 mg/dL
Borderline-high 200 to 239 mg/dL 130 to 159 mg/dL
High 240 mg/dL 160 mg/dL
Modified from National Cholesterol Education Program: ATP III Guidelines At-A-Glance Quick Desk Reference, NIH Pub No 01-3305, Washington, DC, 2001, US Department of Health and Human Services; Public Health Service; National Institutes of Health; National Heart, Lung, and Blood Institute.
Food Cholesterol versus Blood Cholesterol (4 of 5)
Health guidelines
>300 mg of dietary cholesterol per day
>200 mg of dietary cholesterol per day if LDL level is elevated
Total fat intake and blood cholesterol levels
Checking labels
Dietary cholesterol
Saturated fats
Strategies
Food Cholesterol versus Blood Cholesterol (5 of 5)
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Natural fat replacers
Simplesse: made from blending protein from milk or eggs in microparticulation
Carrageenan: thickener extracted from seaweed
Synthetic fat replacers
Salatrim: 5 kcal/g
Olestra: 0 kcal/g
Synthetic Fats and Fat Replacers
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Energy intake
Fat is more efficient being stored in body than carbohydrate and protein.
High-fat foods are low in fiber and other nutrients.
There is a relationship between dietary fat and body fat.
Awareness of dietary fat intake sources can make a difference.
Energy Intake
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Directly related to
Coronary vascular disease
Certain types of cancer
Indirectly related to
Type 2 diabetes mellitus and hypertension
Dietary Fat Intake and Diet-Related Diseases
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The most effective way to achieve permanent behavior change is through gradual reduction.
An action plan for gradual reduction (small changes in behavior or food intake) provides structure for achieving goals.
Toward a Positive Nutrition Lifestyle: Gradual Reduction
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