FATS 3

LECTURE SUMMARY: FAT (LIPIDS) PART 3

Course: Nutrition 120.3
Date: March 3, 2026

LEARNING OBJECTIVES

  • Understand how lipoproteins deliver fat to the cells.

  • Understand how the body uses energy from fat consumed in the diet.

  • Describe ketone bodies.

  • Describe insulin and glucagon in fat metabolism.

  • Understand the repercussions of deficiencies or excess in dietary intake of fats.

TERMS

  • Lipoprotein: A complex of lipids and proteins that transports lipids through the lymphatic and circulatory systems.

  • Lipoprotein Lipase: An enzyme that breaks down triglycerides in lipoproteins into free fatty acids and glycerol.

  • Chylomicrons: The largest type of lipoprotein that carries dietary fat from the intestines.

  • VLDL (Very Low-Density Lipoprotein): A type of lipoprotein made by the liver that carries triglycerides to tissues.

  • HDL (High-Density Lipoprotein): A lipoprotein that returns cholesterol to the liver for disposal.

  • Fatty Acids: The building blocks of triglycerides and phospholipids, crucial for cellular function.

  • Triglycerides: The main constituents of body fat in humans and animals, consisting of three fatty acids.

  • ATP (Adenosine Triphosphate): The energy currency of the cell.

  • Beta Oxidation: The metabolic process by which fatty acids are broken down in the mitochondria to generate Acetyl-CoA.

  • Hormone Sensitive Lipase: An enzyme that hydrolyzes stored triglycerides in adipose tissue into free fatty acids and glycerol.

  • Insulin: A hormone that encourages glucose uptake and lipogenesis while inhibiting lipolysis.

  • Glucagon: A hormone that promotes the release of glucose from stored glycogen and facilitates lipolysis when blood sugar is low.

  • Free Fatty Acid: Fatty acids that are not bound to other molecules and can be used for immediate energy.

OUTLINE FOR LIPID TRANSPORT AND DELIVERY

  1. 7 Steps of Lipid Transport and Delivery

  2. Energy Production

  3. Insulin and Glucagon Fat Metabolism

  4. Medical Conditions Related to Fats

THE 7 STEPS FOR LIPID TRANSPORT AND DELIVERY

  1. From the Intestine to the Blood:

    • Dietary fats are emulsified in the small intestine forming micelles, which are absorbed into chylomicrons and transported via lymph vessels to the bloodstream.

  2. Lipoprotein Lipase Action:

    • Lipoprotein lipase breaks down triglycerides in chylomicrons into free fatty acids and glycerol, which enter surrounding cells.

  3. Chylomicron Remnants:

    • Remaining components (cholesterol + fat-soluble vitamins) travel to the liver for disassembly.

DETAILED EXPLANATION OF LIPOPROTEINS

Chylomicrons

  • Largest type of lipoproteins, high in triglycerides.

  • Formed in the mucosal cells of the intestine and pass into lymph.

  • Broken down by lipoprotein lipase into fatty acids for absorption in cells.

VLDL

  • Smaller than chylomicrons, they transport lipids from the liver.

  • At tissues, lipoprotein lipase breaks down triglycerides, allowing cells to absorb the fatty acids.

  • Removal of fatty acids results in formation of IDL (Intermediate-Density Lipoprotein).

LDL (Low-Density Lipoprotein)

  • Higher in cholesterol, transports fats and cholesterol to body cells.

  • Binds to LDL receptors to enter cells for utilization.

HDL

  • High-density lipoproteins that collect cholesterol from tissues and return it to the liver.

  • They prevent cholesterol buildup in arteries and facilitate disposal.

COMBINED STEPS OF LIPID TRANSPORT

  1. VLDL Transport:

    • VLDLs transport lipids away from the liver.

    • Lipoprotein lipase breaks down triglycerides into fatty acids absorbed by cells, resulting in the formation of IDL.

  2. IDL Transformation:

    • IDL particles either return to the liver or are converted into LDL particles in the bloodstream.

ENERGY PRODUCTION (ATP)

  • Triglycerides are stored or broken down daily.

  • When food is consumed, it provides immediate energy.

  • In absence of food, triglycerides are broken down to release energy:

    • Used during sleep, fasting, or low-energy activities (e.g., watching TV).

METABOLISM OF TRIGLYCERIDES

  1. Glycerol Contribution:

    • Glycerol enters metabolism to produce ATP or small amounts of glucose.

  2. Fatty Acids Transformation:

    • Fatty acids transported to mitochondria undergo beta-oxidation, splitting into Acetyl-CoA, which enters the citric acid cycle to generate ATP and water.

    • This process requires oxygen.

  3. Ketone Body Formation:

    • In the absence of oxygen or glucose, the liver converts fatty acids into ketones as an alternative fuel source, which enter the bloodstream.

ROLE OF INSULIN IN FAT METABOLISM

  • Insulin elevates when blood glucose increases.

  • It promotes:

    • Glucose storage as glycogen in muscle and liver.

    • Activation of lipoprotein lipase, which encourages triglyceride uptake from chylomicrons by adipose tissue.

    • Inhibition of hormone-sensitive lipase, preventing free fatty acids from entering the bloodstream.

ROLE OF GLUCAGON IN FAT METABOLISM

  • In the case of low blood sugar (fasting):

    • Insulin levels are low, allowing hormone-sensitive lipase to rise and release free fatty acids into the bloodstream.

    • Free fatty acids are utilized by tissues like the liver and muscle for energy.

    • This process conserves glucose for the brain, as free fatty acids cannot be used for brain energy needs.

    • In prolonged starvation, the brain adapts to utilize ketone bodies as fuel.

ESSENTIAL FATTY ACID DEFICIENCY

  • Recognized in both infants and adults receiving intravenous nutrition without fat.

  • Signs and Symptoms:

    • Scaly dermatitis.

    • Alopecia (hair loss).

    • Hepatomegaly (swollen liver).

    • Thrombocytopenia (low platelet count leading to bruising).

    • Fatty liver.

    • Anemia.

ESSENTIAL FATTY ACIDS

  • Omega-3 (alpha-linolenic acid, ALA) and Omega-6 (linoleic acid, LA):

    • Both acids serve as precursors for eicosanoids, which help regulate functions like blood clotting, blood pressure, and immune responses.

    • ALA is anti-inflammatory, while LA promotes inflammation, contributing to different health conditions.

  • Their balance is essential in maintaining health and preventing chronic diseases.

IMPACT OF DIET ON CANCER

  • High saturated fat intake is linked to increased cancer risk, particularly breast and colon cancers.

  • The Mediterranean diet, rich in omega-3 fatty acids, is associated with reduced cancer risk.

CARDIOVASCULAR DISEASE (CVD)

  • Defined as heart disease, the second leading cause of death in Canada, accounting for 30% of all deaths.

  • Influenced by diet and lifestyle patterns.

  • Diets including Mediterranean and DASH diets are beneficial for heart health.

ATHEROSCLEROSIS DEVELOPMENT

  • Involves the accumulation of lipids and fibrous materials in arterial walls, decreasing elasticity and blood flow.

  • Characterized by inflammatory processes and plaque formation, leading to potential blockage of arteries.

RISK FACTORS FOR CVD

  • Family history of heart disease (males before 55, females before 65).

  • Presence of diseases: Diabetes, high blood pressure, obesity.

  • Unhealthy blood lipid profiles:

    • High LDL cholesterol.

    • Low HDL cholesterol.

    • High total cholesterol and triglycerides.

  • Lifestyle factors: Smoking, inactivity, and dietary imbalances.

REDUCING CHOLESTEROL LEVELS

  • Can be achieved by consuming soluble fiber, omega-3s, soy protein, and plant sterols while reducing saturated fats and increasing physical activity.

CONCLUSION

  • Additionally covered topics will follow in the next sessions, focusing on advanced aspects of lipid metabolism and their implications on health.