LK

NST 10: Epidemic of Overweight and Obesity

Epidemic of Overweight and Obesity: Chemistry of Fats, Health Consequences, Confounding Factors Marc K. Hellerstein, M.D., Ph.D.

I) What is Fat, Chemically?

  • Chemical Definition; Dietary Fat

    • Fat belongs to a family of compounds called lipids. They are not easily soluble in water and are energy-dense.

    • Fat is chemically known as triacylglycerol (TAG) or triglyceride (TG).

    • It consists of fatty acids (FA) bound to glycerol.

    • Fatty acids provide concentrated energy, specifically 9 \text{ kcal/g}.

  • Why Do We Store Fat in Our Body?

    • Fat is an amazing evolutionary invention for animals due to its energy density.

    • Dense energy storage without requiring water (hydration) is more efficient for mobile organisms.

  • Normal Human Body Composition

    • Animals, including humans, have a large capacity to store fat, unlike carbohydrates or proteins.

    • Body Composition Basics:

      • Water: Approximately 60-70 \% in children, and ~50 \% in adults.

      • Cells (Lean Tissue) / Protein: Composed of about 20 \% protein. For example, ~30 \text{ kg} of muscle contains 20 \% protein, which is 6 \text{ kg} of protein. Given that protein provides 4 \text{ Kcal/kg}, this equates to 24,000 \text{ Kcal}. This is true for almost all cells.

      • Maximum Carbohydrate Stores: These are minuscule.

        • Liver: Approximately 5 \% of 1.5 \text{ kg} liver is 75 \text{ g} of carbohydrate. At 4 \text{ Kcal/g}, this is 300 \text{ Kcal}.

        • Muscle: Less than 1 \% of 30 \text{ kg} muscle is 300 \text{ g} of carbohydrate. At 4 \text{ Kcal/g}, this is 1200 \text{ Kcal}.

      • Most Body Energy Stores: Are in triglycerides (TG) within adipose tissue.

        • Total energy content of fat in the body can be estimated as ~20 \% of a 70 \text{ kg} person's weight, which is ~17.5 \text{ kg}. At ~9 \text{ Kcal/g}, this totals ~160,000 \text{ Kcal}.

        • There is also structural fat and membrane lipids in cells.

  • Body Mass Index (BMI) Categories:

    • Underweight: <18.5

    • Normal: 18.5-24.9

    • Overweight: 25-29.9

    • Obese: 30 and greater

II) Consequences of Overweight/Obesity: Why Care?

  • Some Conditions Associated with Overweight/Obesity:

    • Diabetes mellitus (type 2)

    • High blood pressure

    • Dyslipidemia

    • Cardiovascular disease, Stroke

    • Liver disease (Non-Alcoholic Fatty Liver Disease - NAFLD)

    • Cancers (colon, prostate, breast)

    • Osteoarthritis

    • Gall bladder disease

    • Gastroesophageal Reflux Disease (GERD)

    • Reproductive dysfunction (Polycystic Ovarian Syndrome - PCOS)

    • Early puberty

    • Depression

    • Sleep apnea/breathing disturbances

    • Cognitive dysfunction (Alzheimer's)

  • Focus on Cardiovascular Disease (CVD)

    • Risk Factors: Most are associated with obesity.

      • High blood pressure

      • High cholesterol (LDL)

      • Dyslipidemia (high [TG], low [HDLc], dense LDL, high [apoB])

      • Diabetes (glucose intolerance, impaired fasting glucose)

      • (Obesity)

      • Clotting alterations (dysfibrinolysis)

      • Cigarette smoking

    • Synergistic Effects of Multiple Risk Factors:

      • Most people who develop CVD do not have marked elevations in a single risk factor.

      • More commonly, modest increases in several risk factors are present simultaneously in an individual.

      • This co-occurrence has confounded univariate estimates of risk for individual factors (e.g., high [TG]), as factors combine biologically.

      • Synergistic risk from multiple factors occurring together is well-established.

      • The combination of multiple risk factors has therefore been considered a separate condition, termed a **