"Fats"

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Biochemistry of Fats

Fats are composed primarily of fatty acids and glycerol, forming different classes such as triglycerides, phospholipids, and sterols.

A. Fatty Acids

  • Saturated Fatty Acids (SFA): No double bonds (e.g., palmitic acid, stearic acid).
  • Unsaturated Fatty Acids: Contain one or more double bonds.
    • Monounsaturated (MUFA): One double bond (e.g., oleic acid).
    • Polyunsaturated (PUFA): Multiple double bonds (e.g., omega-3 & omega-6 fatty acids).
  • Trans Fats: Produced via hydrogenation, harmful for health.

B. Glycerides

  • Triglycerides (TG): Three fatty acids attached to glycerol; primary storage form of fat.
  • Diglycerides & Monoglycerides: Intermediates in fat digestion and metabolism.

C. Phospholipids

  • Major components of cell membranes, forming the lipid bilayer.
  • Contain hydrophilic heads (phosphate group) and hydrophobic tails (fatty acids).
  • Examples: Phosphatidylcholine, Phosphatidylserine.

D. Sterols & Lipid Hormones

  • Cholesterol: Precursor for steroid hormones (testosterone, estrogen, cortisol), bile acids, and vitamin D.
  • Eicosanoids: Derived from fatty acids, regulate inflammation and immunity (e.g., prostaglandins, leukotrienes).

Fats in Cell Structure

Fats are fundamental to cellular integrity and function, primarily forming membranes and acting as signaling molecules.

A. Lipid Bilayers & Membrane Fluidity

  • Phospholipids form the bilayer, providing structural integrity.
  • Cholesterol regulates membrane fluidity by preventing rigidity or excessive permeability.
  • Lipid Rafts: Microdomains enriched with cholesterol and sphingolipids, crucial for signaling.

B. Intracellular Signaling

  • Lipids act as second messengers (e.g., diacylglycerol in signal transduction).
  • Fatty acid-derived molecules influence metabolic pathways and gene expression.

3. Fat Metabolism

Fat metabolism is highly regulated, involving breakdown (lipolysis, β-oxidation) and synthesis (lipogenesis, ketogenesis).

A. Fatty Acid Oxidation (β-Oxidation)

  • Occurs in mitochondria & peroxisomes, breaking down fatty acids into acetyl-CoA.
  • Acetyl-CoA enters the Krebs cycle (TCA cycle) → ATP generation via oxidative phosphorylation.

B. Ketogenesis (Alternative Energy Pathway)

  • In fasting/starvation, excess acetyl-CoA is converted to ketone bodies (acetoacetate, β-hydroxybutyrate).
  • Ketones serve as an energy source for the brain & muscles when glucose is scarce.

C. Lipogenesis (Fat Storage & Synthesis)

  • Excess carbohydrates → Converted into fatty acids via acetyl-CoA carboxylase & fatty acid synthase.
  • Fatty acids are stored as triglycerides in adipose tissue.

D. Lipoproteins & Fat Transport

  • Chylomicrons: Transport dietary fats from intestines to tissues.
  • VLDL, LDL, HDL: Transport lipids in the bloodstream.
    • LDL ("bad cholesterol"): Delivers cholesterol to tissues.
    • HDL ("good cholesterol"): Removes excess cholesterol.

4. Health Effects of Fats

Fats play both protective and harmful roles depending on their type and consumption levels.

A. Beneficial Effects

✅ Energy Source: Provides 9 kcal/g, more than carbohydrates or proteins.
✅ Essential Fatty Acids: Omega-3 (EPA, DHA) & Omega-6 regulate brain function, heart health, and inflammation.
✅ Supports Cell Function: Phospholipids, cholesterol, and lipid-derived messengers are essential for cell function.
✅ Aids Vitamin Absorption: Fat-soluble vitamins (A, D, E, K) require fats for absorption.

B. Harmful Effects (Excess or Poor Quality Fats)

❌ Obesity & Metabolic Syndrome: Excess fat storage increases insulin resistance & diabetes risk.
❌ Cardiovascular Disease (CVD):

  • High saturated & trans fats elevate LDL cholesterol → Atherosclerosis.
  • PUFA (omega-3) can reduce CVD risk.
    ❌ Inflammation & Autoimmune Disorders:
  • Excess omega-6 (pro-inflammatory) vs. omega-3 (anti-inflammatory) imbalance.
    ❌ Neurological Impact:
  • Deficiency in essential fatty acids can impair cognition, mood, and neuroprotection.

5. Fat Activity & Energy Utilization

Fats dynamically shift between storage and usage based on metabolic demands.

A. Energy Storage vs. Mobilization

  • Fed state: Lipogenesis → Storage in adipose tissue.
  • Fasting state: Lipolysis → Fatty acids released for energy.
  • Exercise: β-Oxidation predominates during low-intensity endurance activity.

B. Role of Hormones in Fat Metabolism

  • Insulin: Promotes fat storage by activating lipogenesis.
  • Glucagon & Epinephrine: Stimulate lipolysis for energy release.
  • Leptin & Ghrelin: Regulate appetite and fat metabolism.

C. Thermogenesis & Fat Oxidation

  • Brown Adipose Tissue (BAT): Generates heat via uncoupling proteins (UCP1).
  • White Adipose Tissue (WAT): Stores energy, but excessive accumulation leads to obesity.

Conclusion

Fats are not just an energy source but also critical in membrane structure, metabolism, signaling, and health. Understanding the biochemistry, metabolism, and health effects of fats can help optimize nutrition and disease prevention.


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