Lipids: Triglycerides, Phospholipids & Sterols

• Lipids are naturally occurring organic compounds
• The compounds are hydrophobic or amphipathic
• Lipids include fats, oils, waxes, certain vitamins, and similar molecules
• In food, lipids provide energy, support absorption of fat-soluble vitamins (A, D, E, K), and add flavor/texture

Lipid Classification

• Lipids are classified based on structure, function, and properties
• In food they are generally classified as:
  • Triglycerides
  • Phospholipids
  • Sterols

Triglycerides (Fats and Oils)

• Composed of three fatty acids attached to a glycerol molecule
• Fats are solid at room temperature, mainly from animal sources
• Oils are liquid at room temperature, mostly from plant sources
• Triglycerides provide a dense source of energy
• They enhance flavor, and add texture to food
• Examples include butter, olive oil, coconut oil, and animal fats.

Phospholipids

• Structure is similar to triglycerides
• Composed of two fatty acids and a phosphate group attached to glycerol
• Amphipathic properties allow formation of emulsions, stabilizing mixtures of water and oil
• Act as emulsifiers, helping blend ingredients that typically don't mix
• An example is Lecithin, often found in egg yolks and soybeans

Sterols

• Features a complex ring structure, unlike the linear chains of fatty acids
• Important for cell membrane structure
• Cholesterol is a well-known sterol in animal products
• They contribute to the synthesis of important hormones and vitamins
• Cholesterol is found in animal products such as meat and egg yolks
• Plant sterols are found in nuts and seeds

Fatty Acids (Saturated, Monounsaturated, Polyunsaturated, Trans)

• Saturated fatty acids have no double bonds in the carbon chain
  • Found in animal fats, butter, coconut oil
• Monounsaturated fatty acids (MUFA) feature one double bond
  • Found in olive oil, avocado
• Polyunsaturated fatty acids (PUFA) contain multiple double bonds
  • Includes omega-3 and omega-6 fatty acids
  • Found in fish, flaxseed, walnuts
• Trans fatty acids come from partial hydrogenation
  • Solidifies oils
  • Associated with increased health risks
  • Found in processed foods like margarine and baked goods

Essential Fatty Acids (EFAs)

• The body cannot synthesize them
• Must be obtained through diet
• Primary EFAs are omega-3 and omega-6 fatty acids.
• EFAs are crucial for brain health, inflammation control, and cell membrane structure

Types of Essential Fatty Acids

• Omega-3 Fatty Acids
  • Alpha-linolenic acid (ALA) is the main essential omega-3 fatty acid
  • Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are beneficial omega-3s derived from ALA
  • The body's ability to convert ALA into EPA and DHA is limited
• Omega-6 Fatty Acids
  • Linoleic acid (LA) is the main essential omega-6 fatty acid
  • It can be converted into other omega-6 fats like arachidonic acid (AA)
  • AA plays roles in inflammation and immune response

Functions of Essential Fatty Acids

• Cell Membrane Health: EFAs are key components
  • They help maintain flexibility, fluidity, and integrity
• Brain and Eye Health: DHA is important for brain and retinal health
  • Supports cognitive function, memory, and visual development
• Inflammation and Immune Function: EFAs are precursors to signalling molecules called eicosanoids
  • Regulate inflammation, immunity, and blood clotting
• Heart Health: Omega-3 fatty acids help reduce inflammation
  • Improve cholesterol profiles, and may lower blood pressure

Food Sources of Essential Fatty Acids

• Omega-3 Sources:
  • ALA: Flaxseeds, chia seeds, hemp seeds, walnuts, and canola oil
  • EPA and DHA: Fatty fish (salmon, sardines, trout, mackerel) and seafood
  • Algal oil (vegan source of DHA)
• Omega-6 Sources:
  • Linoleic acid: Vegetable oils (sunflower, corn, soybean, safflower oils), nuts and seeds
• Balance Between Omega-3 and Omega-6
  • Modern diets often have a high intake of omega-6 relative to omega-3
  • High omega-6 to omega-3 ratio may promote inflammation
  • Balancing EFAs can be achieved by including more omega-3-rich foods

Functions of Lipids

• Energy Storage
  • Triglycerides serve as a major energy reserve
  • More energy-dense than carbohydrates and proteins (9 kcal per gram)
  • Fats provide a concentrated energy source
• Structural Components
  • Phospholipids are essential components of cell membranes
  • Provide structural integrity and fluidity
  • Cholesterol is a structural component of cell membranes
  • Involved in maintaining membrane fluidity and function
• Insulation and Protection
  • Lipids insulate the body
  • Thermal insulation helps maintain body temperature
  • Cushion and protect vital organs (heart, liver, kidneys) from physical shocks
• Absorption of Fat-Soluble Vitamins
  • Necessary for the absorption of fat-soluble vitamins (A, D, E, K)
• Production of Hormones and Signalling Molecules
  • Serve as precursors to hormones and other signalling molecules
  • Cholesterol is a precursor for steroid hormones (estrogen, testosterone, cortisol)
  • Certain fatty acids are precursors to eicosanoids
  • Involved in inflammation and immune responses
• Flavour and Satiety in Food
  • They contribute to the flavour, texture, and mouthfeel of foods
  • Fats slow down digestion, enhancing feelings of satiety and fullness
• Energy Source During Starvation
  • Stored fats are broken down into fatty acids and ketone bodies
  • Can be used as an alternative energy source

Lipid Sources

• Animal Sources:
  • Meat and Poultry: Beef, pork, lamb, chicken, and turkey contain fats, particularly saturated fats
  • Dairy Products: Milk, cheese, butter, and cream contain significant amounts of fats, including saturated fats and cholesterol
  • Fish and Seafood: Salmon, trout, sardines, and mackerel are rich in omega-3 fatty acids
  • Eggs: A good source of cholesterol and other fats, contain both saturated and unsaturated fats
• Plant-Based Sources:
  • Nuts and Seeds: Almonds, walnuts, chia seeds, and flaxseeds are rich in unsaturated fats, particularly omega-3 and omega-6 fatty acids
  • Avocados: Rich in monounsaturated fats, which promote heart health
  • Olives and Olive Oil: High in monounsaturated fats, which have anti-inflammatory and heart-health benefits
  • Coconuts and Coconut Oil: High in saturated fats, medium-chain triglycerides may have different health effects compared to animal-based saturated fats
• Processed and Packaged Foods:
  • Baked Goods and Pastries: Often contain added fats in the form of hydrogenated oils (trans fats) or saturated fats
  • Snack Foods: Chips, crackers, and other processed snacks can contain significant amounts of fats, sometimes including trans fats
  • Margarine and Shortening: Contain hydrogenated or partially hydrogenated oils, which can include trans fats
• Oils and Fats for Cooking:
  • Vegetable Oils: Canola, soybean, sunflower, and corn oil are high in polyunsaturated and monounsaturated fats
  • Butter and Ghee: Derived from animal milk, butter and clarified butter (ghee) contain saturated fats
  • Palm Oil: High in saturated fats, commonly used in processed foods
  • Balance can be achieved by focusing on unsaturated fats from plants and fish

Recommended Dietary Allowances

• 6 fatty acids and 3 fatty acids ratio should be 5-10:1
• Total Fat Intake
  • Adults: 20-35% of total daily calories
  • For a 2,000-calorie diet, this is approximately 44-78 grams of fat per day
  • Children: Ages 1-3 years: 30-40% of total calories Ages 4-18 years: 25-35% of total calories
  • Pregnant and Lactating Women: May have slightly higher fat needs to support fetal and infant growth
• Saturated Fat
  • Limit intake to less than 10% of total daily calories
  • For a 2,000-calorie diet, this is about 20 grams of saturated fat per day
  • Reducing saturated fat to about 5-6% of calories can further reduce the risk of heart disease
• Trans Fat
  • Intake should be avoided as much as possible
  • Associated with increased heart disease risk
• Essential Fatty Acids
  • Omega-3 Fatty Acids: ALA (Alpha-linolenic acid): Men: 1.6 grams per day Women: 1.1 grams per day EPA and DHA: 250-500 mg of combined EPA and DHA per day is generally recommended for heart health
  • Omega-6 Fatty Acids (Linoleic Acid): Men: 17 grams per day Women: 12 grams per day
• Monounsaturated and Polyunsaturated Fats
  • There is no specific RDA
  • Most of the fats in the diet should come from unsaturated sources
  • Sources include olive oil, nuts, seeds, avocados, and fish