db week2 nutr.
Chapter 5 Lipids: Not Just Fat
What Are Lipids?
Essential nutrients
Provide energy
Help transport fat-soluble nutrients throughout the body
Contribute greatly to the flavor and texture of food
What Are Lipids?
Term applied to a variety of substances
Triglycerides
Stored in adipose tissue in the body
Called fats and oils in food
Phospholipids
Found in foods of both plant and animal origin
Also made by the body
Soluble in fat and water
Sterols
Includes cholesterol
Fatty Acids Are Key Building Blocks
Fatty acid
Determines whether a fat is solid or liquid at room temperature
Fatty Acids Are Key Building Blocks
Chain length
Fatty acids differ in chain length
Lengths vary from 4 to 24 carbons
Grouped as short-chain, medium-chain, and long-chain
Fatty Acids Are Key Building Blocks
Chain Length
Shorter fatty acids remain liquid at room temperature and even with refrigeration
Shorter fatty acids also are more water-soluble
Fatty Acids Are Key Building Blocks
Saturation
Saturated fatty acid
When all bonds between carbon atoms in a chain are single bonds
Unsaturated fatty acid
When one or more bonds between carbon atoms is a double bond
Fatty Acids Are Key Building Blocks
Saturation
Monounsaturated fatty acid
When there is one carbon–carbon double bond
Polyunsaturated fatty acid
When there is more than one carbon–carbon double bond
Fatty Acids Are Key Building Blocks
Cis vs. trans
Unsaturated fatty acids can vary in shape
Cis fatty acids
Chain is bent
Occur naturally
Trans fatty acids
Chain is straighter
Produced by hydrogenation
Fatty Acids Are Key Building Blocks
Essential and Nonessential Fatty Acids
Nonessential fatty acids
Not “essential” to have in your diet
Can be made in the body when they are needed
Fatty Acids Are Key Building Blocks
Essential and Nonessential Fatty Acids
Essential fatty acids
Must come from food
Cannot be made by the body
Two families
Omega-3 (alpha-linolenic acid) and omega-6 (linoleic acid)
Pre-cursors to eicosanoids
Triglycerides
Structure
Glycerol + three fatty acids
Most fatty acids exist as part of triglyceride molecules
Triglycerides
Functions
Energy source
9 kcal/g
Energy reserve
Stored energy in adipose tissue
Insulation and protection
Visceral fat
Triglycerides
Functions
Carrier of Fat-Soluble Compounds
Improves intestinal absorption and bioavailability during digestion
Sensory Qualities
Contributes to food’s flavor, odor, and texture
Triglycerides in Food
Found in a variety of fats and oils
Classified by their most prevalent type
Triglycerides in Food
Commercial processing of fats
Reduces waste, prevents spoilage, increases availability of calorie-rich oils
Removes damaging free fatty acids
Adds antioxidants to delay rancidity and extend shelf life
Triglycerides in Food
Commercial processing of fats
Negatives
Removes potentially healthful phospholipids, plant sterols, and other phytochemicals
Further processing into solid fats increases the proportion of trans fatty acids
Phospholipids
Structure
Glycerol + two fatty acids + phosphate group
Compatible with both fat and water
Phospholipids
Functions
Ideal emulsifiers
Keep fat suspended in water
Keep oil and water mixed
Perfect structural element for cell membranes
Able to communicate with watery environments of blood and cell fluids
Allows other lipids to enter and exit cells
Phospholipids
Cell membranes
Double layer of phospholipids
Selectively allow both fatty and water-soluble substances into the cell
Store fatty acids temporarily
Plays an important role in nerve cells
Phospholipids
Lipid Transport
In the stomach
Break fats into tiny particles for digestion
In the intestine
Continue emulsifying fat
In the blood
Coat the surface of the lipoproteins that carry lipid particles to their destinations in the body
Phospholipids
Emulsifiers (lecithin)
Lecithin used as an emulsifier to combine two ingredients that don’t ordinarily mix, such as oil and water
Allows ingredients in salad dressing to mix well and remain mixed, for example
Phospholipids in Food
Occur naturally in plants and animals, but in much smaller amounts than triglycerides
Abundant in egg yolks, liver, soybeans, peanuts
Not a dietary essential
Sterols
Have a multiple-ring structure
Best known example is cholesterol
Most contain no fatty acid
Sterols
Cholesterol Functions
Major structural component of all cell membranes
Precursor of important substances, including
Vitamin D
Sterol hormones
Bile salts
Sterols
Cholesterol Synthesis
Primarily made in the liver
Sterols in Food
Found only in foods of animal origin
Typical American consumers between 250-700 mg of cholesterol and 250 milligrams of plant sterols per day
Lipid Digestion and Absorption
Digestion of Triglycerides and Phospholipids
Mouth
Chewing and lingual lipase start digestion
Stomach
Breaks triglycerides down to diglycerides and free fatty acids
Small intestine
Bile and pancreatic lipase emulsify and break down the fats for absorption
Intestinal cells absorb glycerol and fatty acids into the bloodstream
Lipid Digestion and Absorption
Lipid absorption
Micelles
Water-soluble globules with a fatty core
Carry monoglycerides and long-chain fatty acids to microvilli
Bile recycling pathway known as enterohepatic circulation
Lipid Digestion and Absorption
Lipid absorption
Lipoprotein
Cylomicron
Deliver dietary lipids from intestines to cells and liver
Lipid Digestion and Absorption
Digestion and absorption of sterols
Body absorbs about 50% of dietary cholesterol
Dietary fat increases absorption
Plant sterols and dietary fiber decrease absorption
Transportation of Lipids in the Body
Lipids packaged into lipoprotein carriers in order to travel in the bloodstream
Lipoproteins differ by size, density, and the composition of their lipid cores
Transportation of Lipids in the Body
Chylomicrons
Form in the intestinal tract
Enter the lymphatic system
About 90 percent fat
Liver uses remnants as raw material for very-low-density lipoproteins
Transportation of Lipids in the Body
Very-Low-Density Lipoproteins (VLDLs)
Deliver triglycerides to cells
Transportation of Lipids in the Body
Intermediate-Density Lipoproteins (IDLs)
Converted to low-density lipoproteins
Transportation of Lipids in the Body
Low-Density Lipoproteins (LDLs)
Deliver cholesterol to cells
Transportation of Lipids in the Body
High-Density Lipoproteins (HDL)
Pick up cholesterol for removal or recycling
Recommendations for Fat Intake
Recommended intake
Reduce saturated fat, trans fat, and cholesterol
Total fat: 20–35% of calories
Less than 10% of calories from saturated fat
Less than 300 mg per day of cholesterol
Recommendations for Fat Intake
Essential fatty acid requirements
Linoleic acid should provide about 2% of calories
Omega-6 and omega-3 balance
Ratio of 6:1 omega-6 to omega-3 fatty acids
Seafood (fatty fish), canola or soybean oil
Recommendations for Fat Intake
Current dietary intakes
Americans eat ~33% of total calories from fat
Average calorie intake has increased = Americans consuming more total grams of fat
Saturated fat intake ~11%
Cheese, pizza, grain-based desserts, chicken, sausage, etc.
Recommendations for Fat Intake
Role of fat replacers
Different types of composition
Olestra
Sucrose + fatty acids
Indigestible— provides no calories
Reduces absorption of fat-soluble vitamins
Lipids and Health
Heart disease
Major risk factors
High blood cholesterol
High LDL and low HDL
Smoking
High blood pressure
Lipids and Health
Reducing heart disease risk
AHA diet and lifestyle recommendations
Consume an overall healthy diet
Aim for a healthy body weight
Aim for a desirable lipid profile
Aim for normal blood pressure
Aim for normal blood glucose levels
Be physically active
Avoid use of and exposure to tobacco products
Lipids and Health
Reducing heart disease risk
AHA recommendations
Balance calorie intake and physical activity to achieve or maintain a healthy body weight
Consume a diet rich in fruits and vegetables
Choose whole-grain, high-fiber foods
Consume fish, especially oily fish, at least twice a week
Limit your intake of saturated and trans fat and cholesterol
Lipids and Health
Reducing heart disease risk
AHA recommendations (cont.)
Minimize your intake of beverages and foods with added sugars
Choose and prepare foods with little of no salt
If you consume alcohol, do so in moderation
Follow the AHA recommendations when eating outside of the home
Lipids and Health
Obesity
High-fat diets promote weight gain
Significant within the U.S. population
34.9% of American adults
17% of American children and adolescents
Lipids and Health
Metabolic syndrome
Affects ¼ of American adults
Cluster of at least three symptoms
Excess abdominal fat
High blood glucose
High serum triglycerides
Low HDL cholesterol
High blood pressure
Lipids and Health
Cancer
Results from complex mix of lifestyle, hereditary, and environmental factors
Role of nutrition and diet complex
Evidence suggests 30-40% are due to poor food choices and physical inactivity
Some dietary factors act as promoters, while others serve a protective role
Lipids and Health
Cancer
Dietary and lifestyle factors for reducing cancer risk
Maintain a healthful weight
Adopt a physically active lifestyle
Consume a healthy diet
Limit alcohol consumption
Lipids and Health
Putting It All Together
Healthy People 2020 objectives target reducing deaths from heart disease and stroke and reducing the number of adults with high blood cholesterol levels