Nutrition: Fats

Chapter 5: Lipids

Introduction

  • Content created with contributions from Dr Devries, Aboud, and Cengage.

The Role of Fat

The Good

  • Body Fat: Insulates organs and aids in temperature regulation.

  • Energy Storage: Provides energy for sustained physical activity.

  • Nutrient Transport: Carries fat-soluble vitamins (A, D, E, K).

  • Culinary Qualities: Enhances taste and improves texture by making food softer, easier to chew, and swallow.

  • Dietary Impact: Lowers glycemic index of carbohydrate foods.

The Bad

  • Excess Body Fat: Linked to weight gain and increased risk of heart disease.

  • Dietary Fat: Effects on health vary based on fat type.

Types of Fats and Fatty Acids

  • Fat and Fatty Acids: Comprise sterols, phospholipids, and triglycerides (fats and oils).

  • Energy Content: Triglycerides (C and H) provide more energy per gram than carbohydrates (CHO).

  • Common Fatty Acids: 18C triglycerides; fatty acids have a methyl and an acidic end.

  • Unsaturated Fatty Acids: Lacking hydrogen atoms, categorized as:

    • Monounsaturated: One double bond.

    • Polyunsaturated: More than one double bond.

  • Essential Fatty Acids: Include omega-3 (linolenic acid) and omega-6 (linoleic acid) – necessary for human health.

  • Triglyceride Composition: 1 glycerol + 3 fatty acids, typically a mix (5% of dietary fat).

Omega Fatty Acids

  • Sources:

    • Omega-3: Found in flaxseed, fish oils, canola, and walnut oils.

    • Omega-6: Sources include sunflower, safflower, corn, and soybean oils.

Role of Lipids in the Body

Triglycerides

  • Energy Contribution: Provide 9 kcal/g and serve as an unlimited energy storage form.

  • Adipose Tissue Functions: Secretes hormones (adipokines) that can be inflammatory, especially in obesity.

  • Additional Roles: Insulation, shock absorption, structural materials for cell membranes, and cell signaling.

  • Fatty Acids: Properties such as saturation and carbon length affect food function and health.

Characteristics of Solid Fats and Oils

Firmness

  • Influence of Saturation:

    • Saturated fats are firm at room temperature.

    • Shorter carbon chains lead to softer fats (coconut oil softer than butter).

Stability

  • Rancidity:

    • Saturated fats are more stable than polyunsaturated fats.

    • Oxygen exposure can spoil fats; light and heat accelerate rancidity.

  • Prevention Strategies:

    • Store in airtight, dark bottles and refrigerate, adding antioxidants (e.g., Vitamin E), or using hydrogenation.

Trans Fats

  • Formation:

    • Rarely found naturally; created during processing and hydrogenation (cis to trans conversion).

  • Health Concerns: Behave like saturated fats; linked to worse health outcomes. Canada banned partially hydrogenated oils in 2020.

Phospholipids and Sterols

  • Phospholipids (5% of dietary fat):

    • Composed of one fatty acid replaced by phosphate and choline.

    • Emulsifiers critical for cell membranes and lipid transport.

  • Sterols:

    • Cholesterol sourced from animals; plant sterols may reduce dietary absorption of cholesterol.

    • Essential for bile acids, hormones, and vitamin D production.

Lipid Digestion, Absorption, and Transport

Digestion Process

  • Triglyceride Absorption: Requires breakdown into monoglycerides and fatty acids aided by bile (emulsifies fats).

Enterohepatic Circulation

  • Bile reabsorbed into the liver for reuse; some lost in feces, preventing bacterial overgrowth in the intestine.

Absorption Mechanism

  • Short and Medium-Chain Fatty Acids: Directly enter the blood.

  • Long-Chain Fatty Acids: Form micelles with bile for absorption into intestinal cells, reassembled into triglycerides.

Lipid Transport

  • Lipoproteins: Four types distinguished by lipid and protein content:

    • Chylomicrons: Transport dietary triglycerides.

    • VLDL: Circulates triglycerides from the liver.

    • LDL: Delivers cholesterol to cells; associated with heart disease.

    • HDL: Collects excess cholesterol and returns it to the liver; protective against plaque buildup in arteries.

Cholesterol Sources

Exogenous vs. Endogenous

  • Endogenous: Produced by the liver (800-1500 mg/day) as LDL and VLDL; high LDL linked to plaque buildup and heart disease.

  • Exogenous: Dietary intake (~350 mg/day); has minimal effect on blood cholesterol levels.

Health Implications of Lipids

Influence of Lifestyle

  • Genetics, healthy body weight, dietary pattern (favored fats), and physical activity can modulate LDL and HDL levels.

Essential Fatty Acids and Their Role

  • Omega-6 and Omega-3 fatty acids contribute to key bodily functions, including cell membrane structure and hormone production.

Dietary Recommendations

  • Daily Intake Guidelines:

    • Linoleic acid (5-10%) and linolenic acid (0.6-1.2%); limit saturated fats to <10% and minimize trans fats.

    • Ensure 20-35% energy from fats to meet fat-soluble vitamin needs.

Lipid Metabolism

  • Energy Usage: Triglycerides in adipose cells can be hydrolyzed into free fatty acids for energy, especially at rest.

Dietary Impact on Health

  • Increased LDL: Linked to cardiovascular disease and blood pressure elevations from saturated and trans fats.

  • Decreased LDL: Benefits include lower cardiovascular risk, improvement of blood lipids, and reduced inflammation with monounsaturated and polyunsaturated fats.

Major Sources of Various Lipids

Potentially Healthful Lipids

  • Monounsaturated Fats: Found in avocados, nuts, and certain oils.

  • Omega-6: Found in oils, margarine, and various seeds.

  • Omega-3: Present in fatty fish, flaxseed, chia seed, and walnuts.

Potentially Harmful Lipids

  • Commonly include saturated and trans fats found in processed foods, fatty meats, and certain dairy products.