Structure Phospholipids
Similar to triglycerides but only 2 FA and 1 Phosphate Lecithin Function Foods Emulsifier Body Emulsifier Fat digestion (bile) Fat transport in the blood (lipoproteins) Constituent of cell membranes
Phospholipid Bilayer in Cell Membrane
Watery fluid Outside cell Glycerol heads
Fatty acid tails
Inside cell
Watery fluid
Phospholipid Bilayer
Sources Production in the body Eggs, liver, soybeans, wheat germ, peanuts Supplements hydrolyzed by intestinal lecithin lipase
Sterols
Structure Cholesterol Function Tissues Structural component of cell membranes Precursor of bile acids 50% of daily cholesterol productions used for bile Hormone synthesis Sex hormones Vitamin D Adrenal hormone Blood Transport of fats in blood as part of lipoproteins
Sterols
Produced in the body Plant sterols appear to block or reduce the absorption of dietary cholesterol
Digestion of Fat
Digestion of Fat / Phospholipids
Very minor digestion
Mouth Lingual lipase Stomach Lingual lipase stable to acid Gastric lipase
Major breakdown Small Intestines
Bile - emulsifier Pancreatic lipase Enzymes on intestinal wall (lesser amount)
Bile is an Emulsifier
Digestion of Triglyceride
Lipase
Bile Reabsorption
Enterohepatic circulation Once fat digestion is complete, most of the bile (99%) is reabsorbed in the ileum, complexes to albumin, sent back to the liver via the portal vein; 1% is excreted in the feces (trapped in fibers)
Absorption of Fat Vascular System
Small fat fragments
Glycerol Short chained fatty acids Medium chained fatty acids
Lymphatic System
Large fat fragments
Monoglycerides Long chained fatty acids
Assembly of lipoproteins in intestinal cell
Chylomicrons
Lipoproteins
Chylomicron VLDL LDL "bad cholesterol" HDL "good cholesterol"
Chylomicron
Package that carries digested fats into the lymph Surface Phospholipids Proteins Inside Triglycerides Cholesterol
Lipoproteins
Roles of Fat
Energy
very energy dense: 9 kcal per gram major energy used during rest used for energy during exercise, especially after glycogen is depleted energy storage 3500 kcals per pound of fat
Roles of Fat
Fat-soluble vitamins
Vitamins A, D, E, and K Fat is required for their absorption and transport
Essential to many body functions
Cell membrane structure Nerve cell transmissions Protection of internal organs Insulation to retain body heat
Roles of Fat
Provides flavor and texture to foods Contributes to sense of satiation
Fats are more energy dense than carbohydrates or protein Fats take longer to digest
Health Risk Associated Cardiovascular Disease
Cardiovascular disease Dysfunction of the heart or blood vessels Can result in heart attack or stroke Risks Overweight Physical inactivity Smoking High blood pressure Diabetes mellitus
Health Effects of Dietary Lipids
The type of fat in our diet can contribute to or protect against cardiovascular disease Dietary Cholesterol
minor effect on blood cholesterol levels
Fatty acids
Saturated Monounsaturated Polyunsaturated
Health Effects of Dietary Lipids
Diets high in saturated fats
Decrease the removal of LDLs from the blood
Increase LDL
Increase cholesterol levels in the blood Contribute to the formation of plaques that can arteries
Health block Effects of Dietary Lipids
Diets high in monounsaturated fats
Decreases LDL blood cholesterol levels when replacing saturated fats No effect on HDL
Blood Cholesterol and Risk for Heart Disease
High levels of LDL increase risk for Heart Disease High levels of HDL decreases risk for Heart Disease
Health Effects of Dietary Lipids
Omega 6 fatty acids
Linoleic acid
Essential Food sources
Oils (linoleic acid) polyunsaturated oils
Health Effects of Dietary Lipids
Omega 6 fatty acids
Converted to Arachidonic acid Precursor to eicosonoids --> prostaglandins / thromboxanes Decreases blood cholesterol in hypercholesterolemic adults Encourages clot formation Promotes tumor growth Sources Arachidonic acid also comes from dietary meats
Health Effects of Dietary Lipids
Omega 3 Fatty Acids
Alpha- linolenic acid
Essential Food sources
Canola, Soybean Oils
Flax Walnut
Health Effects of Dietary Lipids
Omega 3 Fatty Acids
Alpha-linolenic acid (omega-3) Found in vegetable oils and leafy green Converted to EPA and DHA in relatively minor amounts EPA and DHA Precursors to eicosonoids prostaglandins/thromboxanes Reduces triglycerides in blood Inhibits blood clot formation May inhibit cancer development
Linolenic Acid Content of Selected Vegetable Oils, Nuts, and Seeds
Linolenic Acid Content given Olive oil Walnuts, English Soybean oil Canola oil Walnut oil Flaxseeds Flaxseed (linseed) oil in g/tbsp 0.1 0.7 0.9 1.3 1.4 2.2 8.5
Data for this table and seafood table are from the USDA Nutrient Data Laboratory
Food sources of EPA and DHA
Seafood is a rich source of omega-3 fatty acids
EPA and DHA Remember, alpha-linolenic acid is converted but not in high amounts
Some eggs are also a good source of omega-3 fatty acids
omega-3 EPA and some DHA hens are fed a diet rich in omega-3
Health Effects of Dietary Lipids Omega 6 : Omega 3
Imbalance > 10:1 Recommend levels 4:1
Problems Compete for same enzyme systems Dietary considerations Eat more fish / less meat Fish oil supplements
Health Effects of Dietary Lipids
Fish Oil
supplements
Can increase bleeding time Removal of metals, toxins, vitamin A has improved - be careful! Make sure that Vitamin E added to protect fatty acids from oxidation Enteric coated fish oils decrease aftertaste Expensive!!
Health Effects of Dietary Lipids
Trans fatty acids
Increases blood cholesterol levels
Raises LDL / lowers HDL
Mandatory labeling in 2002
Lipid Recommendations
Acceptable Macronutrient Distribution Range (AMDR) for fat: 20-35% of calories Minimize saturated and trans fatty acid Active people may need more energy from carbohydrates
20-25% of total calories
Recommended Levels of Lipids in the Diet Therapeutic Lifestyle Change Lifestyle changes can prevent or reduce
cardiovascular heart disease
Total fat intake: 20-35% total calories Saturated fat: less than 7% total calories Cholesterol: less than 300 mg per day Trans fat: reduce to absolute minimum Increase omega-3 fatty acids Dietary fiber: 20-30 grams per day Folate: 400 micrograms/day
Artificial Fat - Olestra
Engineered fat
Sucrose + fatty acids No kilocalories Heat stable Looks and feels like fat
Artificial Fat - Olestra
Safety Concerns
Decreased absorption of fat soluble vitamins GI distress
FDA Approved foods