Dietary Fats Overview and Digestion Process

Dietary Fats - Objectives

• Identify essential fats and lipids in the diet
• Describe the chemical nature and functions of fats in the human body
• List food sources of various lipids and essential fatty acids
• Determine the appropriate amount and type of fats for daily intake
• Understand fat digestion, absorption, and metabolism
• Understand the effects of deficient and excessive fat consumption

Dietary Fats - Digestion

• Mouth: No chemical digestion, fat broken into smaller particles by chewing and mixed with saliva
• Stomach: Peristaltic movements mix food with gastric juice. Two enzymes (gastric lipase and pancreatic lipase) aid in fat digestion. Fats are emulsified in the stomach, and main digestion begins in the small intestine
• Small Intestine: Duodenum stimulates bile secretion from the gallbladder. Bile acts as an emulsifier, breaking down large fats into smaller particles, increasing the efficiency of enzyme action. Alkaline nature of bile assists pancreatic lipase in removing fatty acids from triglycerides, converting them into diglycerides and monoglycerides, and finally into fatty acids and glycerol.

Dietary Fats - Absorption

• Via Hepatic Portal Vein: Some medium-chain fatty acids and monoglycerides are absorbed through this route (10-12 carbon atoms)
• Via Lymph System: Fatty acids and monoglycerides are resynthesized to form triglycerides. Chylomicrons (lipoproteins) are formed with phospholipids, cholesterol, and specific proteins (apoproteins). Water-insoluble triglycerides are transported as lipoproteins.

Dietary Fats - Metabolism

• After absorption, fat can be oxidized by body tissues to produce energy (CO2 + H2O) or stored in fat deposits
• Unlike carbohydrates (limited glycogen storage), fat storage can vary considerably.
• Carbohydrates can be converted to fat and stored
• Fatty acids are not a primary source of blood glucose but rather a source of ketone bodies, which can be used for energy by most tissues if glucose is unavailable.

Dietary Fats – Breakdown

• Fat is broken down into glycerol and fatty acids
• Glycerol participates in the glycolytic pathway and can form glucose (gluconeogenesis) under certain conditions
• Fatty acids are broken down into acetyl CoA, which can enter the TCA cycle or form acetoacetate (in the liver), producing ketone bodies that are released into the bloodstream
• Most tissues (except brain) can break down ketone bodies into CO2 and H2O, generating ATP through the citric acid cycle and the respiratory chain

Dietary Fats – Interrelationship

• Fats, proteins, and carbohydrates interact in metabolic pathways

Dietary Fats – Food Sources

• Most foods (except bread, cereals, and most fruits) contain varying percentages of lipids. Some are visible (added fats), others are hidden (naturally occurring fats in food items). Important sources include milk, egg yolks, oily fish, and meat.
• Plant sources include oils from seeds (e.g., groundnut, sesame, soybean, rice bran, coconut, almond, cashew nut, corn, safflower, sunflower), as well as hydrogenated fats and margarine.
• Animal sources include mutton, fish, poultry, milk, milk products, cheese, eggs, and organ meats.

Dietary Fats – Deficiency

• Deficiency of fats leads to a deficiency of essential fatty acids, impacting cell membranes and their permeability.
• Symptoms may include eczema, skin lesions (particularly dry, scaly lesions and papules on limbs) in infants.
• Growth and weight may also be affected, along with the absorption of fat-soluble vitamins.

Dietary Fats – Excessive Intake

• Fat consumption percentages vary significantly across regions and income groups.
• Fats should provide 20-25% of total calories.
• Excessive fat intake causes obesity, elevated blood cholesterol, and increases the risk of cardiovascular diseases.
• Omega-3-rich foods have a protective effect.

Dietary Fats – Recommended Intake

• Fat contribution to total calories should be 30% maximum.
• Saturated fat (kcal) should not exceed 10% of total calories.
• Polyunsaturated fats (PUFAs) should be at least 10% of calories to provide essential fatty acids.
• The ratio of omega-3 and omega-6 fats should be maintained.
• Cholesterol intake should not exceed 180 mg/day.

Dietary Fats – Reducing Fat Intake

• Use skim milk and its products
• Choose lean meats and trim off visible fat
• Use healthy cooking methods like steaming, boiling, or poaching instead of frying
• Limit or avoid salad dressings, and opt for low-fat options.
• Select fruits over pastries for desserts
• Use herbs, spices, and lime juice instead of fats for flavoring food

Dietary Fats - Types of Fats

• Saturated Fats: No double bonds (solid at room temperature) - found in animal fats, butter.
• Monounsaturated Fats: One double bond (liquid at room temperature)- found in olive oil, avocados, nuts.
• Polyunsaturated Fats: Two or more double bonds (liquid at room temperature) - found in vegetable oils, etc
• Essential fatty acids: Body cannot synthesize, must obtain from diet- linoleic acid & linolenic acid

Dietary Fats - Introduction

• Lipids are insoluble in water but soluble in fat solvents. They are primarily composed of carbon, oxygen, and hydrogen. Lipids provide more energy than carbohydrates and proteins.
• Key types of lipids include fatty acids, fats, oils, phospholipids, lipoproteins, and sterols.

Dietary Fats – Functions

• Energy: Fats are a concentrated energy source
• Protein Sparing: Sufficient fat intake lets proteins focus on growth and maintenance
• Thermal Insulation: Subcutaneous fat insulates and helps maintain body temperature.
• Protection: Fat pads protect vital organs.
• Absorption of Fat-Soluble Vitamins: Essential for the absorption of vitamins (A, D, E, and K)
• Essential Fatty Acids: Needed for hormone production and cell membrane health
• Cell Membrane Synthesis: Crucial component of all cell membranes.
• Satiety: Fats slow down digestion, promoting a feeling of fullness.

Dietary Fats - Classification of Lipids

• Simple lipids: Consisting mostly of triglycerides (glycerol + 3 fatty acids) - the major form of dietary fat.
• Compound lipids: Include phospholipids (associated with cell membranes) and glycolipids.
• Derived lipids: Products of lipid breakdown, including glycerol, fatty acids, and cholesterol.
• Sterols: Including cholesterol (important component of cell membranes and involved in hormone synthesis).

This quiz focuses on the essential fats and lipids required in the human diet, their chemical nature, and their functions. It also covers the digestion and absorption processes of fats, including the roles of various organs and enzymes in fat metabolism.