Study Notes: Fat Loss and Metabolism

Study Notes: Fat Loss and Metabolism

Types of Body Fat

• Subcutaneous fat – directly under the skin, can be inches thick, covers muscles (e.g., abs, deltoid).

• Visceral fat – surrounds internal organs (heart, intestines). Linked to metabolic syndrome, type 2 diabetes, hypertension, cardiovascular disease.

• Both subcutaneous and visceral fat are lost through similar processes.

What Happens When We Burn Fat

1. Storage form – Fat is stored in adipocytes as triglycerides (glycerol + 3 fatty acids).

2. Breakdown (Lipolysis)

   • Enzyme: hormone-sensitive lipase.

   • Activated by epinephrine, norepinephrine, cortisol.

   • Breaks triglycerides into free fatty acids + glycerol.

3. Transport

   • Fatty acids are hydrophobic.

   • Transported in blood by albumin (like a “taxi”).

4. Uptake into muscles

   • Fatty acids travel via blood → muscle fibers → mitochondria.

   • Used to make ATP aerobically (oxygen required).

5. ATP yield

   • Glucose → 32–36 ATP.

   • Palmitic acid (common FA) → ~113 ATP.

   • Fat = higher energy yield, but slower to mobilize.

Why Not Burn Fat All the Time?

• Logistics: Fat requires mobilization, transport, and oxygen → slower.

• Carbs: Stored as glycogen in muscle, ready for quick energy.

• Exercise: Takes 10–20 minutes of steady activity before fat metabolism ramps up.

Spot Reduction Myth

• Cannot choose where fat is pulled from.

• Example: Doing crunches won’t preferentially reduce belly fat.

• Muscle hypertrophy (growth) can improve visibility, but overall fat loss is systemic.

The "Fat-Burning Zone"

• At low intensity: higher proportion of fat burned vs carbs.

• At higher intensity: more total fat calories burned despite lower proportion.

• Example:

  • Light session: 100 kcal burned, 70% fat → 70 kcal from fat.

  • Intense session: 500 kcal burned, 30% fat → 150 kcal from fat.

• Key: Total caloric expenditure matters more than proportion.

Exercise and Fat Loss

• No single “best” exercise. Many modalities work:

  • Running, cycling, intervals, weight training, sports.

• Consistency and enjoyment = biggest predictors of success.

• Athletes across sports have low fat despite different training methods.

Key Factors in Fat Loss

1. Caloric balance – Burn more calories than consumed.

2. Consistency – Regular activity, not occasional bursts.

3. Individual limits – Genetics, age, hormones influence outcomes.

4. Control what you can – Diet, activity, lifestyle.

 Summary:

• Fat loss = shrinking adipocytes through lipolysis, transport, and oxidation.

• Spot reduction is a myth → focus on overall fat loss.

• Different exercises can work as long as total energy expenditure is high and consistent.

• Best results come from activities you enjoy and can sustain.