Fats, Oils, and Lipids: Comprehensive Study Notes
Module 5: Fats, Oils, and Lipids
What Are Fats and Why Do You Need Them?
Lipids: A category of compounds composed of carbon, hydrogen, and oxygen that are hydrophobic (insoluble in water).
Fat: The common name for one type of lipid, specifically a triglyceride.
Functions of Fats in Foods:
Contribute to flaky texture in baked goods.
Make meats tender.
Provide flavor and aromas.
Contribute to satiety (feeling of fullness).
Important Functions of Fats and Other Lipids in the Body:
Energy storage.
Insulation to maintain body temperature.
Transport of compounds in the blood.
Form the structure of cell membranes.
Three Main Types of Lipids found in foods and the body:
Triglycerides (commonly called fats).
Phospholipids.
Sterols.
The basic unit of triglycerides and phospholipids is the fatty acid.
Fatty Acids in Triglycerides and Phospholipids
Fatty Acids: Chains of carbon and hydrogen atoms with an acid group ( ext{COOH}) at one end.
There are over 20 different types of fatty acids.
They can vary by:
Length of the carbon chain.
Whether carbons have single or double bonds between them.
The total number of double bonds.
Three Main Types of Fatty Acids:
Saturated Fatty Acids:
All carbons are bonded to hydrogen atoms, meaning no double bonds between carbons.
Tend to be solid at room temperature (e.g., stearic acid, which has 18 carbons).
Monounsaturated Fatty Acids (MUFAs):
Contain one double bond in their carbon chain.
Tend to be liquid at room temperature (e.g., oleic acid, with 18 carbons, found in olive oil).
The double bond creates a bend in the carbon chain.
Polyunsaturated Fatty Acids (PUFAs):
Contain more than one double bond in their carbon chain.
Examples include the essential fatty acids linoleic acid (an omega-6 fatty acid) and alpha-linolenic acid (an omega-3 fatty acid), found in soybean oil.
Multiple double bonds create multiple bends in the carbon chain.
Triglycerides: The Most Common Lipid
Triglyceride: Composed of three fatty acids connected to a glycerol backbone.
This is the most common lipid found in both foods and the body.
Often referred to simply as "fats."
Saturated fats mostly contain saturated fatty acids.
Unsaturated fats mostly contain unsaturated fatty acids.
Oils are fats that are liquid at room temperature.
Phospholipids: Structure and Role in Cell Membranes
Phospholipids: Have a glycerol backbone, but are linked to two fatty acids and a phosphorus-containing group.
The phosphorus-containing head is hydrophilic (attracts water and charged particles).
The fatty acid tail is hydrophobic (repels water).
Cell membranes are constructed as a phospholipid bilayer, arranging with hydrophilic heads facing outwards (towards watery extracellular fluid) and inwards (towards watery cytoplasm), and hydrophobic tails facing each other in the lipid interior.
This creates a barrier that controls what enters and leaves the cell.
A major phospholipid in cell membranes is lecithin.
Lecithin is also used as an emulsifier in foods (e.g., salad dressings) to prevent oil and water from separating.
Sterols: Unique Ring Structure
Sterols: Composed mainly of four connecting rings of carbon and hydrogen atoms.
Cholesterol is a primary example of a sterol.
Important roles of cholesterol:
Integral part of cell membrane structure.
Precursor for other critical compounds in the body (e.g., converted into vitamin D, bile acids, and sex hormones).
Cholesterol is not required in the diet because the body synthesizes all the cholesterol it needs.
How Fat Is Digested, Absorbed, and Transported
Digestion of Fat:
Mouth: Chewing initiates mechanical digestion; lingual lipase in saliva begins chemical digestion of fats.
Stomach: Peristalsis churns food; gastric lipase breaks down some fats into diglycerides and one fatty acid.
Small Intestine: Most fat digestion occurs here.
Bile acids (produced by the liver, stored in the gallbladder) are secreted into the small intestine to emulsify fat, breaking large fat globules into smaller pieces.
Cholecystokinin (CCK), a hormone, stimulates the pancreas to release enzymes.
Pancreatic lipase further breaks down emulsified fats into two fatty acids and a monoglyceride.
The by-products of fat digestion (monoglycerides and fatty acids) are packaged with lecithin from bile into micelles (small carriers) for transport through the intestinal wall cells.
Absorption and Transport of Fat:
Short-chain fatty acids are absorbed directly into the bloodstream and travel to the liver.
Long-chain fatty acids, cholesterol, phospholipids, and other remnants are repackaged inside the intestinal cells to form chylomicrons (a type of lipoprotein) for transport into the lymphatic system.
Lipoproteins: Transport fat through the lymph and blood.
Chylomicrons: Carry digested dietary fat (triglycerides, cholesterol, phospholipids) from the small intestine, through the lymph, and into the bloodstream to body cells. Lipoprotein lipase helps break down fat from chylomicrons. Remnants are dismantled in the liver.
Very Low-Density Lipoproteins (VLDL): Produced mainly in the liver; deliver fat (endogenous triglycerides) made in the liver to cells primarily in muscle and fat tissue. Once fatty acids are taken up by cells, VLDLs transform into LDLs.
Low-Density Lipoproteins (LDL, "bad" cholesterol): Formed from VLDLs; release cholesterol into body cells. LDLs not taken up by cells can degrade and release cholesterol that may adhere to blood vessel walls, contributing to plaque formation.
High-Density Lipoproteins (HDL, "good" cholesterol): Produced by the liver; circulate in the blood, picking up excess cholesterol from cells and blood vessel walls (a process called reverse cholesterol transport) and delivering it back to the liver for excretion through bile, thereby removing it from the bloodstream.
How Your Body Uses Fat and Cholesterol
Functions of Fat
Energy-Dense Fuel: Provides 9 calories per gram, more than double carbohydrates or protein.
Energy Release: Glucagon stimulates the release of fat from fat cells to provide energy for the heart, liver, and muscles when blood glucose levels decline.
Vitamin Absorption: Essential for the absorption of fat-soluble vitamins (A, D, E, K) and carotenoids.
Insulation: Insulates the body to help maintain body temperature.
Cushioning: Cushions bones, organs, and nerves, protecting them from shock and injury.
Essential Fatty Acids
Two polyunsaturated fatty acids are essential because the body cannot synthesize them and they must be obtained from the diet:
Linoleic acid: An omega-6 fatty acid.
Alpha-linolenic acid: An omega-3 fatty acid.
Roles of Essential Fatty Acids:
Help maintain healthy skin cells, nerves, and cell membranes.
They are precursors to eicosanoids: These are hormone-like substances involved in regulating inflammation, blood clotting, and blood pressure.
Alpha-linolenic acid is a precursor to longer-chain omega-3 fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
EPA and DHA are considered heart-healthy fatty acids.
Rich sources include fatty fish such as salmon, herring, and sardines.
Functions of Cholesterol
Cell Membrane Component: A vital part of cell membranes, contributing to fluidity and structure.
Precursor: Serves as a precursor for the synthesis of:
Vitamin D.
Bile acids (essential for fat digestion).
Sex hormones (e.g., estrogen, testosterone).
Dietary Cholesterol vs. Blood Cholesterol: Dietary cholesterol has less impact on circulating blood cholesterol levels than the intake of saturated and trans fats. The body produces all the cholesterol it requires.
Dietary Recommendations for Fat Intake
Total Fat Intake:
Acceptable Macronutrient Distribution Range (AMDR) from the Dietary Reference Intakes (DRI): 20 to 35 percent of total daily calories should come from fat.
Note that dietary fat provides 9 calories per gram, which is more than twice the calories per gram of carbohydrates or protein.
Saturated Fat Intake:
For heart health, consume less than 10 percent (ideally less than 7 percent) of your total daily calories from saturated fats.
Calculation examples for a 2,000-calorie diet:
Total fat (at 20-35%): (2,000 imes 0.20) ext{ calories/day} imes (1 ext{ g fat} ext{ / } 9 ext{ calories}) = 44 ext{ grams/day} to (2,000 imes 0.35) ext{ calories/day} imes (1 ext{ g fat} ext{ / } 9 ext{ calories}) = 78 ext{ grams/day} (Range: 44-78 grams daily).
Saturated fat (at 7-10%): (2,000 imes 0.07) ext{ calories/day} imes (1 ext{ g fat} ext{ / } 9 ext{ calories}) = 16 ext{ grams/day} to (2,000 imes 0.10) ext{ calories/day} imes (1 ext{ g fat} ext{ / } 9 ext{ calories}) = 22 ext{ grams/day} (Max: 22 grams daily).
Essential Fatty Acid Intake:
Linoleic acid (omega-6): Between 5 and 10 percent of total calories.
Alpha-linolenic acid (omega-3): 0.6 to 1.2 percent of total calories.
Trans Fat Intake:
Minimize consumption in the diet.
Trans fats are created through hydrogenation, a process that adds hydrogen atoms to unsaturated fats, converting some double bonds from a cis to a trans configuration. This makes them more solid at room temperature, resistant to rancidity, and increases shelf life.
Trans fats are considered worse for heart health than saturated fats because they both raise LDL cholesterol and lower HDL cholesterol.
The FDA has banned partially hydrogenated oils (the primary source of artificial trans fats) in processed foods.
Cholesterol Intake:
The body makes all the cholesterol it needs; thus, dietary intake is not essential.
Healthy individuals over the age of 2 are advised to limit dietary cholesterol to less than 300 ext{ mg} daily.
Recent research suggests that dietary cholesterol has less impact on blood cholesterol levels compared to saturated fat intake.
Major Food Sources of Fats
Healthier Fats: Foods containing unsaturated fats (both monounsaturated and polyunsaturated fats) are generally better for health.
Monounsaturated fats (MUFAs): Peanut oil, canola oil, olive oil, nuts, avocados.
Polyunsaturated fats (PUFAs): Abundant in vegetable oils (e.g., soybean oil, corn oil, sunflower oil, safflower oil), as well as soybeans, walnuts, flaxseeds, and wheat germ.
Essential Fatty Acids (Linoleic and Alpha-linolenic): Good sources include vegetable oils, nuts, and flaxseeds.
Omega-3 Fatty Acids (EPA and DHA): Rich sources include fatty fish like salmon, herring, mackerel, sardines, and tuna (light, canned in water).
Saturated Fat Sources: Major contributors in the American diet include fatty meats, cream, butter, whole milk, cheese, and certain oils (e.g., coconut oil, palm kernel oil, palm oil).
Fat Substitutes in Food Products
Purpose: Designed to provide the creamy properties of fat with fewer calories and total fat grams.
Since fat provides 9 calories/gram, fat substitutes can potentially reduce calories from fat by more than 50 percent.
Types of Fat Substitutes:
Carbohydrate-based: The majority of fat substitutes. Use plant polysaccharides (e.g., fibers from grains like Beta-Trim, cellulose like Avicel cellulose gel, gums like Slendid, polydextrose like Litesse, modified food starch like STA-SLIM). These act as gelling agents, thickeners, or provide texture/mouthfeel.
Protein-based: E.g., Microparticulated Protein (Simplesse), used to enhance mouthfeel in dairy products, salad dressings, and spreads.
Fat-based: Modified fats that provide fewer calories or are used in smaller amounts. E.g., Mono- or Diglycerides (Dur-Lo) for mouthfeel/moisture retention; Short-Chain Fatty Acids (Salatrim) for mouthfeel; Olestra (Olean), a synthetic fat that provides 0 calories and 0 grams of fat.
Important Note: "Fat-Free" does not always mean "Calorie-Free." Fat-free products may still contain significant calories from carbohydrates and other ingredients (e.g., fat-free fig bars vs. regular fig bars have a difference of only 10 calories, but 2 grams less fat).
Atherosclerosis and Heart Disease Risk
Heart Disease: Often begins with a buildup in the arteries, a process called atherosclerosis.
Atherosclerosis: The narrowing of coronary arteries due to the buildup of plaque.
Plaque is hardened debris composed of cholesterol-laden foam cells, platelets, calcium, protein fibers, and other substances.
It is thought to begin with an injury to the lining of the arteries, often contributed by:
High blood pressure.
High cholesterol levels.
Smoking.
This plaque buildup and narrowing impedes the flow of oxygen-rich blood to the heart and other organs.
It also increases the chance of blood clots blocking the vessel, which can lead to a heart attack or stroke.
Development of Atherosclerosis:
Arterial Injury: The artery's lining is injured, attracting immune cells and prompting inflammation.
Lipids Accumulate: Lipids, particularly oxidized LDL cholesterol, seep beneath the artery wall lining. Immune cells (e.g., white blood cells) engulf these oxidized LDLs and transform into foam cells.
Fatty Streak: The foam cells accumulate to form a fatty streak, which releases more toxic and inflammatory chemicals.
Plaque Formation: The foam cells, along with platelets, calcium, protein fibers, and other substances, form thick deposits of plaque, stiffening and narrowing the artery. Blood flow is reduced or obstructed.
Risk Factors for Heart Disease
Factors You Cannot Control:
Age.
Gender (men generally have higher risk earlier).
Family history of heart disease.
Type 1 diabetes mellitus.
Factors You Can Control:
Physical Inactivity: Regular exercise can help lower LDL ("bad") cholesterol and raise HDL ("good") cholesterol.
Excess Weight: Losing excess weight can help increase HDL levels.
Smoking: Quitting smoking can significantly increase HDL levels and reduce arterial damage.
Type 2 Diabetes Mellitus.
High Blood Pressure.
A low HDL cholesterol level.
A high LDL cholesterol level.
Other Potential Risk Factors:
High levels of homocysteine.
Lp(a) protein.
C-reactive protein (a marker of inflammation).
Apolipoprotein B (Apo B).
Metabolic Syndrome: A cluster of risk factors that significantly increases the risk of heart disease, stroke, and type 2 diabetes. It includes:
Insulin resistance.
High blood pressure.
Centralized obesity (excess abdominal fat).
Low HDL cholesterol levels.
High triglyceride levels.
Maintaining Healthy Blood Cholesterol Levels and Reducing Heart Disease Risk
Minimize Saturated Fats, Trans Fats, and Dietary Cholesterol: Follow dietary recommendations to limit these (See "Dietary Recommendations for Fat Intake" above).
Include Fish in Your Weekly Choices: Fatty fish are rich in heart-healthy omega-3 fatty acids (EPA and DHA).
Eat Plenty of Plant Foods:
Plant foods are naturally cholesterol-free.
Soluble fiber-rich foods: Can help decrease LDL cholesterol levels (e.g., oats, barley, legumes, fruits, vegetables).
Phytosterols: Plant sterols similar in structure to cholesterol, found in plant cell membranes (e.g., soybean oil, many fruits, vegetables, legumes, sesame seeds, nuts, cereals). They help lower LDL cholesterol by competing with cholesterol for absorption in the intestinal tract.
Select Foods Rich in Antioxidants and Phytochemicals:
Antioxidants: May help reduce LDL cholesterol levels by preventing its oxidation (a key step in atherosclerosis).
Flavonoids: Phytochemicals found in fruits, vegetables, tea, nuts, and seeds. They offer antioxidant protection and may inhibit platelet aggregation, which can lead to blood clot formation.
Strive for Plenty of Exercise and Manage Your Weight: Regular physical activity and maintaining a healthy weight improve lipoprotein profiles (lower LDL, raise HDL) and overall cardiovascular health.
Moderate Use of Alcohol: May reduce the risk of heart disease for some individuals, but many should avoid alcohol entirely (e.g., those with certain medical conditions or a history of alcoholism).
The Whole is Greater Than the Sum of Its Parts: Emphasizes that a holistic approach encompassing various healthy dietary and lifestyle choices provides greater benefits than focusing on individual components.
Interpreting Blood Cholesterol Levels (in mg/dL)
Total Cholesterol Level:
<200: Fabulous!
200–239: Borderline high.
\geq 240: High.
LDL Cholesterol Level:
<100: Fabulous!
100–129: Near or above optimal.
130–159: Borderline high.
160–189: High.
\geq 190: Much too high!
HDL Cholesterol Level:
\geq 60: Fabulous!
40–60: Good.
<40: Too low.
The Traditional Mediterranean Diet
A traditional diet pattern of the Mediterranean region is consistently associated with a lower risk of heart disease and cancer.
Lifestyle Components: Emphasizes a very active lifestyle, long and relaxing family meals, afternoon naps, and a supportive community.
Dietary Components: Primarily a plant-based diet rich in whole grains, fruits, vegetables, legumes, and nuts.
Olive oil is the principal fat source.
Includes low-fat dairy and ample water.
Occasional consumption of fish, poultry, eggs, red meat, sweets, and wine (in moderation).
Mercury and Fish Consumption (Real-World Nutrition)
Methylmercury: A toxic chemical that can accumulate in larger, longer-lived fish.
It is particularly harmful to the developing nervous systems of unborn children.
High-mercury fish include: swordfish, shark, king mackerel, and tilefish (from the Gulf of Mexico).
Recommendations for Women of Childbearing Age and Young Children:
These populations should avoid the four high-mercury fish listed above.
Pregnant women and women of childbearing age should consume 8 to 12 ounces of other varieties of fish weekly.
Ideally, this means 2–4 two-ounce servings per week from the "Best Choices" list or 1 serving from the "Good Choices" list.
Canned albacore (white) tuna has more mercury than canned light tuna (made from skipjack).
Limit albacore tuna intake to 6 ext{ ounces/week}.
Children starting at age 2 can be served 1 to 2 two-ounce servings of fish per week from the low-mercury options.
The Coconut Oil Debate: Is It Healthy?
Arguments for Coconut Oil's Health Benefits:
It is a good source of vitamin E.
Some studies suggest it may help raise HDL levels more than olive oil.
Arguments Against Coconut Oil's Health Benefits:
Other plant-based oils (e.g., sunflower oil) are also excellent sources of vitamin E and are typically lower in saturated fat.
Olive oil also contains beneficial phytochemicals and is widely recognized as heart-healthy.
Despite some claims, coconut oil is very high in saturated fat (e.g., 88% saturated fat, significantly higher than butter or beef fat), which is generally advised to be limited for heart health.