1. Basal Metabolic Rate (BMR)

• Definition: The energy your body uses at complete rest, in a thermoneutral environment, after ~8 hours of sleep and ~12 hours of fasting.

• Function: Keeps vital organs working—heart pumping, lungs breathing, brain active, body temperature regulated.

• Contribution: ~60–70% of total daily energy expenditure (TDEE).

• Determinants: Age, sex, body size, lean body mass, genetics, hormones (thyroid, catecholamines).

2. NEAT (Non-Exercise Activity Thermogenesis)

• Definition: Calories burned from daily non-exercise activities—walking around the house, fidgeting, cooking, cleaning, standing.

• Contribution: Highly variable; ~15–30% of TDEE.

• Key Point: NEAT explains why two people of similar body size can have very different calorie needs.

• Modifiable: Increasing daily movement (taking stairs, standing desk, pacing while on calls) can raise NEAT significantly.

3. Exercise Activity Thermogenesis (EAT)

• Definition: Calories burned from structured physical activity—running, cycling, gym workouts, sports.

• Contribution: ~5–15% of TDEE (can be more in athletes).

• Variability: Depends on intensity, frequency, and type of exercise.

4. Thermic Effect of Food (TEF) (often grouped in discussions)

• Definition: Energy used to digest, absorb, and process nutrients.

• Contribution: ~10% of TDEE.

• Macronutrient effect: Protein has the highest TEF (20–30%), carbs moderate (5–10%), fat low (0–3%).

✅ Summary:

• BMR = baseline life-sustaining energy (~60–70%)

• NEAT = everyday activity energy (~15–30%, very variable)

• EAT = planned exercise (~5–15%)

• TEF = digestion (~10%)

All together = Total Daily Energy Expenditure (TDEE).