Untitled Flashcards Set

I. Introduction to Lipids

• Lipids are a diverse group of hydrophobic molecules that include:

  • Triglycerides (fats and oils)

  • Phospholipids (component of cell membranes)

  • Sterols (cholesterol and plant sterols)

Functions of Lipids in the Body

• Provide energy (9 kcal per gram)

• Store energy in adipose tissue

• Insulate and protect organs

• Aid in the absorption of fat-soluble vitamins (A, D, E, K)

• Form cell membranes and maintain their integrity

• Precursor for hormones (e.g., steroid hormones, vitamin D)

• Serve as emulsifiers (phospholipids like lecithin)

II. Types of Lipids

1. Triglycerides

• Composed of three fatty acids attached to a glycerol backbone.

• Most common type of lipid in foods and in the body (95% of dietary fat).

• Functions:

  • Provide texture in food

  • Enhance flavor and mouthfeel

  • Store energy in adipose tissue

2. Phospholipids

• Structure: Glycerol backbone, two fatty acids, and a phosphate group.

• Function:

  • Major component of cell membranes (phospholipid bilayer).

  • Act as emulsifiers in food (e.g., lecithin in salad dressings).

  • Help transport lipids in the blood.

3. Sterols

• Ring-shaped lipids that do not contain fatty acids.

• Cholesterol is the most well-known sterol.

  • Found in every cell of the body.

  • Precursor for vitamin D, bile acids, and steroid hormones (e.g., estrogen, testosterone).

  • Synthesized by the liver, so it is not essential in the diet.

• Phytosterols and phytostanols (found in plants) help lower LDL cholesterol by competing for absorption.

III. Fatty Acids

Fatty Acids Vary By:

1. Length of Carbon Chain:

   • Short-chain FA: <8 carbons (quickly digested).

   • Medium-chain FA: 8–12 carbons.

   • Long-chain FA: >12 carbons (most common in diet, take longer to digest).

2. Degree of Saturation:

   • Saturated fatty acids (SFA): No double bonds, solid at room temp (e.g., butter, coconut oil, animal fats).

   • Monounsaturated fatty acids (MUFA): One double bond, liquid at room temp (e.g., olive oil, avocado).

   • Polyunsaturated fatty acids (PUFA): Two or more double bonds, liquid at room temp (e.g., sunflower oil, fatty fish).

3. Shape of Fatty Acids:

   • Cis: Naturally occurring, hydrogens on the same side.

   • Trans: Unnatural, hydrogens on opposite sides, created via hydrogenation, increases LDL ("bad" cholesterol).

4. Location of Double Bonds:

   • Omega-3 (α-linolenic acid): First double bond at carbon 3 from the omega end (e.g., flaxseeds, walnuts, fish).

   • Omega-6 (linoleic acid): First double bond at carbon 6 from the omega end (e.g., vegetable oils, nuts).

   • Both omega-3 and omega-6 are essential fatty acids.

IV. Lipid Digestion, Absorption, and Transport

1. Digestion of Lipids

• Mouth:

  • Mechanical digestion (chewing).

  • Lingual lipase begins breaking down medium-chain triglycerides (minor role).

• Stomach:

  • Gastric lipase hydrolyzes some triglycerides into diglycerides and free fatty acids.

• Small Intestine (Main Site of Digestion):

  • Phase 1: Emulsification

    • Bile (from gallbladder) emulsifies fat into smaller droplets.

  • Phase 2: Enzymatic Digestion

    • Pancreatic lipase hydrolyzes triglycerides into monoglycerides and free fatty acids.

    • Phospholipase breaks down phospholipids.

    • Sterols are absorbed intact.

• Large Intestine:

  • Any undigested fats bind to fiber and are excreted.

2. Absorption of Lipids

• Micelles (fat droplets coated with bile) transport lipids across the small intestine.

• Short-chain and medium-chain fatty acids enter the bloodstream via the hepatic portal vein.

• Long-chain fatty acids, phospholipids, and cholesterol are repackaged into chylomicrons and enter the lymphatic system.

3. Transport of Lipids

• Lipids are transported via lipoproteins:

  • Chylomicrons – transport dietary lipids from the small intestine to tissues.

  • VLDL (Very-Low-Density Lipoproteins) – deliver triglycerides to cells.

  • LDL (Low-Density Lipoproteins) – "bad cholesterol," transports cholesterol to cells.

  • HDL (High-Density Lipoproteins) – "good cholesterol," removes excess cholesterol from cells and transports it to the liver for excretion.

V. Lipids and Cardiovascular Disease

1. Atherosclerosis and Coronary Heart Disease

• Atherosclerosis: Narrowing of arteries due to plaque buildup.

  • LDL particles penetrate artery walls and become oxidized, triggering an immune response.

  • Macrophages engulf oxidized LDL, forming foam cells, leading to plaque buildup.

  • Plaque formation can reduce blood flow and lead to heart attack or stroke.

2. Risk Factors for Heart Disease

• Uncontrollable risk factors: Family history, age, gender.

• Controllable risk factors: High LDL cholesterol, low HDL cholesterol, smoking, poor diet, obesity, lack of exercise, high blood pressure, diabetes.

3. Ways to Lower Heart Disease Risk

• Reduce saturated fat and trans fat intake (limit to <10% of total calories).

• Increase omega-3 fatty acids (e.g., fish, flaxseeds, walnuts).

• Eat more fiber-rich foods (fruits, vegetables, whole grains).

• Exercise regularly.

• Quit smoking and manage stress.

VI. Dietary Recommendations for Lipids

• AMDR (Acceptable Macronutrient Distribution Range) for fat:

  • 20–35% of total daily calories from fat.

• Saturated fat: <10% of total daily calories.

• Trans fat: Avoid as much as possible.

• Cholesterol: Not essential in diet (liver produces enough).

• Omega-3 and Omega-6 intake:

  • Omega-3 (ALA, DHA, EPA): 1.1–1.6 g/day.

  • Omega-6 (linoleic acid): 11–17 g/day.

VII. Fat Substitutes

• Used to reduce fat content in processed foods.

• Types:

  • Carbohydrate-based (e.g., gums, fiber) – retain moisture, provide texture.

  • Protein-based (e.g., whey, egg whites) – mimic fat creaminess.

  • Fat-based (e.g., Olestra) – may reduce fat absorption.