Introduction to Nutrition - Module 5: Lipids

KIN275 Introduction to Nutrition

Module 5: Lipids

Instructor Information

  • Host: Julia Totosy de Zepetnek, PhD

  • University: University of Regina

  • Department: Kinesiology & Health Studies

Module 5 Learning Objectives

  1. Discuss lipids (also known as "fats").

  2. Discuss the three types of lipids:

    • Triglycerides

    • Phospholipids

    • Sterols

  3. Discuss lipid transport in the body and its relationship with atherosclerosis.

  4. Discuss the roles of lipids in the body.

  5. Review and discuss dietary lipid recommendations.

Fats – Recommended Intake

  • DRI and AMDR for Total Fat:

    • AMDR: 20-35% of total daily calories

  • DRI AI of Essential Fats:

    • n-3 (Omega-3): 1.1-1.6 g/day

    • n-6 (Omega-6): 12-17 g/day

Fat Intake Statistics

  • Fat intake above 35% is highest in adults aged 31-50 years, with a steady decline in percentage intake among older age groups.

Sources of Dietary Fats

  • Plant-Based Sources:

    • Cottonseed

    • Linseed

    • Canola

    • Sunflower

    • Sesame

    • Olives

    • Coconut

    • Palm

    • Avocados

    • Nuts

    • Seeds

  • Animal-Based Sources:

    • Meat

    • Fish

    • Eggs

    • Poultry

    • Dairy

Types of Fat in Food

  • Visible Fats:

    • Butter, margarine, salad dressings, fats on meat, chicken skin, meat fibers, dairy products, whole grain cereals, nuts, baked goods, eggs.

  • Invisible Fats: Found within food products such as meats based on their leanness, vegetables, grains, and processed foods.

Fats in the Canadian Diet

  • Fat intake in Canada declined from ~40% in 1978 to ~31% in 2004, remaining stable through 2015.

  • Breakdown of Fat Sources:

    • 50% from animal-based fats (meat and alternatives, dairy equivalents).

    • 25% from fast food and baked goods.

Lipid Definitions

  • Lipid: A chemical term for fat, a group of organic molecules that are predominantly hydrophobic.

    • Composition: Carbon, hydrogen, and oxygen; chains of carbon usually between 4-24 chains.

    • Properties: Contribute to the texture, taste, flavor, and aroma of food.

Types of Lipids

  1. Triglycerides (TG):

    • Major form of lipids in food and body; consists of one glycerol molecule and three fatty acids.

  2. Phospholipids:

    • Composed of glycerol, two fatty acids, and a phosphate group; important for cell membranes.

  3. Sterols:

    • Structurally different as they do not contain glycerol or fatty acids; arranged in four rings with various side chains (e.g., cholesterol).

Triglycerides Structure

  • A triglyceride comprises three fatty acids attached to a glycerol molecule.

    • Diglyceride: Two fatty acids attached.

    • Monoglyceride: One fatty acid attached.

    • Formation involves condensation, while breakdown involves hydrolysis.

Fatty Acids Characteristics

  • Ends:

    • Methyl end (CH3) and carboxyl end (COOH).

  • Solubility:

    • Water-soluble at the carboxyl end (hydrophilic), carbon chain is not water-soluble (hydrophobic).

  • Chain Length Types:

    • Short-chain fatty acids (SCFA): <10 carbons

    • Medium-chain fatty acids (MCFA): 10-15 carbons

    • Long-chain fatty acids (LCFA): >16 carbons

Saturation and Properties

  • Degree of Saturation:

    • Degree of saturation affects melting point, firmness, stability.

    • Saturated Fatty Acids: Maximum number of hydrogen bonds; typically solid at room temperature if >10C in chain length.

    • Unsaturated Fatty Acids: Have C=C double bonds creating ‘cis’ kinks, which leads to liquids at room temperature.

    • Monounsaturated (1 double bond) and polyunsaturated (2+ double bonds) fatty acids are important types.

Trans Fat and Health Impact

  • Trans fatty acids: Formed by partial hydrogenation, found in processed foods. Increases LDL cholesterol ('bad' cholesterol) and decreases HDL cholesterol ('good' cholesterol).

  • Health Recommendations: Eliminate trans fats; associated with increased cardiovascular disease risk.

  • Legislation: The FDA's ban on artificial trans fats aims to prevent heart attacks and deaths.

Essential Fatty Acids

  • Omega-3s:

    • Linolenic Acid (ALA): 18:3 \n - Contributes to numerous health aspects including cardiovascular health.

  • Omega-6s:

    • Linoleic Acid (LA): 18:2 \n - Important in cell signaling and inflammation management.

  • The ideal ratio of omega-6 to omega-3 fatty acids is between 1:1 to 5:1, but Western diets tend to be excessively high in omega-6.

Roles of Lipids in the Body

  1. Source of energy and reserve (9 kcal/g).

  2. Carry fat-soluble vitamins (A, D, E, K).

  3. Component of cell membranes; important for brain function.

  4. Regulate body functions including satiety and hormone synthesis.

  5. Provide insulation and protection for organs.

  6. Lubrication of mucous membranes.

Dietary Recommendations for Lipids

  • Intake Guidelines:

    • AMDR for total fat intake varies by age group; should be mindful of balancing saturated fats while ensuring sufficient essential fatty acids intake.

    • Recommendations include low trans fat, low saturated fat, and maintaining a focus on unsaturated fats.

Lipid Digestion and Absorption Process

  1. Begins in the stomach with minor lipid digestion.

  2. The liver produces bile aids in fat digestion in the small intestine.

  3. Pancreatic enzymes break down triglycerides into fatty acids and glycerol.

  4. Micelles facilitate lipid absorption via intestinal cells into the bloodstream or lymphatic system.

  5. Chylomicrons formed from digested lipids transport fats through lymph to the bloodstream.

Lipoproteins

  • Four main types:

    1. Chylomicrons

    2. Very Low-Density Lipoprotein (VLDL)

    3. Low-Density Lipoprotein (LDL)

    4. High-Density Lipoprotein (HDL)

    • Function in transporting triglycerides, cholesterol, and proteins throughout the body.

Atherosclerosis Mechanism

  1. LDL uptake leads to inflammation of blood vessel walls.

  2. LDL oxidation creates foam cells that develop into fatty streaks.

  3. Formation of fibrous plaques that can obstruct blood flow, with complications arising from ruptured plaques.

  4. Risk factors include modifiable (diet, exercise) and non-modifiable (age, genetics) influences.

Conclusion on Dietary Fats

  • Focus should be on type, not just the amount of fat consumed:

    • Incorporate healthy sources like omega-3 fatty acids, avoid trans fats, and maintain balanced diets to manage cholesterol levels and reduce cardiovascular risks.