Lipids: Fats and Fatty Acids Overview

Lipids: Fats, Fatty Acids, and Their Roles

• Fat's beneficial roles: Insulates organs, provides energy for sustained activity, carries fat-soluble vitamins, enhances palatability (tastes good), and makes food easier to chew and swallow. It also decreases the glycemic index of carbohydrate foods.
• Fat's detrimental roles (excess): Leads to weight gain, heart disease, and other health problems.
• Different Fat Impacts: Dietary fat's effects depend on the type of fat (e.g., saturated, unsaturated).
• Fatty Acid Classifications: Fatty acids vary in chain length, saturation, and the location of double bonds.
• Omega Classification: Chemists categorize polyunsaturated fatty acids based on the position of the first double bond from the methyl end (Ω). Omega-3s have the first double bond three carbons from the methyl end, while Omega-6s have the first double bond six carbons away. Omega-9s, like oleic acid, have one double bond nine carbons from the methyl end.

Triglycerides: Body's Primary Energy Storage

• Energy Source: Triglycerides provide 9 kcal per gram of energy.
• Unlimited Storage: Stored in adipose tissue, acting as an unlimited energy reservoir.
• Adipokines: Adipose tissue secretes hormones called adipokines for various body functions. Obesity can cause these hormones to become inflammatory and contribute to insulin resistance.

Solid Fats and Oils: Stability and Rancidity

• Stability: Saturated fats are more stable and less prone to rancidification than polyunsaturated fats.
• Rancidity: Exposure to oxygen, heat, and light accelerates the deterioration of fats (rancidity).
• Reducing Rancidity: Slowing rancidity of fat-containing products can be achieved through proper storage (airtight, dark, refrigerated), use of antioxidants (like Vitamin E), and fat hydrogenation.

Trans Fats: Unhealthy Fats

• Natural Occurrence: Rarely found naturally.
• Hydrogenation: Created through processing and hydrogenation, where some cis double bonds switch to trans during hydrogenation. They also arise from high-temperature food preparation.
• Health Impact: Behave similar to saturated fats, with research indicating a more detrimental effect on health compared to saturated fats.
• Elimination: Many countries, like Canada, have significantly reduced or eliminated the use of partially hydrogenated oils to limit trans fat intake.

Phospholipids and Sterols: Essential Lipids

• Phospholipids: Act as emulsifiers (soluble in fat and water), essential for cell membranes, and for the transport of fats and fat-soluble vitamins to cells.
• Sterols: Plants and animals contain sterols. Cholesterol, exclusively from animals, is a sterol vital for bile acid, sex hormone, adrenal hormone, and vitamin D production, and is a component of cell membranes. Plant sterols, similar in structure to cholesterol, can reduce the absorption of dietary cholesterol.

Digestion, Absorption, and Transport of Lipids

• Digestion Process: Fats begin to melt in the mouth, are emulsified in the stomach, and stimulated further in the small intestine with bile acids to further digest the fat droplets. Digestive enzymes in the stomach and intestines break down fats further.
• Lipid Transport (Lipoproteins): Lipid transport via specialized protein-lipid complexes, called lipoproteins, which are categorized (from largest to smallest) as chylomicrons, VLDL (very-low-density lipoproteins), LDL (low-density lipoproteins), and HDL (high-density lipoproteins).

Exogenous vs. Endogenous Cholesterol

• Endogenous: Liver produces approximately 800-1500 mg of cholesterol daily (which circulates as LDL and VLDL). High levels of circulating LDL are linked to heart disease.
• Exogenous: Dietary cholesterol is typically ~350 mg/day. Dietary cholesterol only modestly increases blood cholesterol and does not trigger a large increase in liver cholesterol production.

Maintaining Healthy Lipid Levels

• Factors lowering LDL and raising HDL: Healthy weight, monounsaturated or polyunsaturated fats, soluble fibre, phytochemicals, moderate alcohol consumption, and physical activity.
• LDL and HDL significance: LDL cholesterol is linked to heart disease, and high LDL and low HDL cholesterol increase risk. Sufficient HDL and low LDL significantly decreases the risk of heart disease.

Essential Fatty Acids and Eicosanoids

• Essential Fatty Acids: Linoleic acid (omega-6) and linolenic acid (omega-3) are essential fats that the body cannot produce and must obtain from food.
• Eicosanoids: Hormone-like compounds derived from omega-6 (pro-inflammatory) and omega-3 (anti-inflammatory) fatty acids that affect localized processes, including blood pressure, clotting, and inflammation.
• Dietary Recommendations: Omega-6 and omega-3 fatty acid intake recommendations exist (DRI values). Replacing saturated fat with polyunsaturated and monounsaturated fats is essential for overall health.