Lecture on Lipids

Overview

• Lipids are hydrophobic molecules.
• Two main dietary sources: Triglycerides and Cholesterol.

Triglycerides

• Consist of glycerol and three fatty acid chains.
• Fatty acids have even numbers of carbons and a carboxyl group.
• Saturated Fats:
  • All single carbon bonds.
  • Found in animal products (meats, dairy) and some tropical oils.
  • Linear structure allows for stacking, creating solids at room temperature (e.g., lard).
• Unsaturated Fats:
  • Some carbons have double bonds.
  • Found in seeds, nuts, and vegetable oils.
  • Double bonds create kinks, preventing stacking, making them liquid at room temperature (oils).
• Trans Fats:
  • Produced via hydrogenation.
  • Have trans configuration, causing poor enzymatic breakdown.
  • Can lead to oily stool due to poor absorption.

Cholesterol

• Found in egg yolks, meats, and milk products.
• Most is produced by the liver.
• Can be converted into different fatty acids by the liver.

Essential Fatty Acids

• Some cannot be synthesized by the body and must be consumed.
• Examples: Linoleic and linolenic acids (found in vegetable oils).

Functions of Lipids

• Aid in absorption of fat-soluble vitamins (A, D, E, K).
• Major fuel source for skeletal muscle and hepatocytes (liver cells).
• Precursor to phospholipids.
  • Phospholipids have dual hydrophobic and hydrophilic characteristics.
• Stored in adipose tissue for energy, protection, and insulation.
• Prostaglandins play roles in muscle contraction, blood pressure control, and inflammation.
• Cholesterol:
  • Building block for steroid hormones (e.g., sex hormones, cortisol, aldosterone).
  • Contributes to cell membrane structure and function.
  • Precursor for bile salts.

Dietary Requirements

• Fats should comprise less than 30% of total caloric intake.
• Saturated fats should be less than 10%.
• Cholesterol intake should not exceed 300 mg per day.
• Circulating cholesterol should be below 200 mg/dL.

Fat Substitutes

• Examples: Air, modified starches, milk whey protein, Olestra.
• Olestra, derived from cottonseed, not metabolized, leads to loose stools.
• Disadvantages:
  • Altered by high heat.
  • Different taste from real fats.
  • May interfere with absorption of fat-soluble drugs and vitamins, causing digestive issues.

Conclusion

• The American diet often exceeds recommended lipid intake, contributing to health issues like obesity.
• Understanding lipid sources and functions is important for nutritional balance.