Metabolism here means the calories you burn in a day. The practical deficit and surplus, including a two-week weigh-in check, is in what TDEE means for weight loss. This page is the four components and the activity setting people get wrong.
The Equation: TDEE
Your Total Daily Energy Expenditure (TDEE) is the number of calories you burn in 24 hours. It is the ceiling.
- Eat > TDEE → Gain Mass.
- Eat < TDEE → Lose Mass.
- Eat = TDEE → Maintain.
TDEE is the sum of four parts. Knowing which part is large tells you where a change actually shows up.
1. BMR (Basal Metabolic Rate) - 60-70%
This is the energy cost of keeping you alive (Brain function, heart beat, cell repair). Even if you slept all day, you would burn this.
- A larger body, whether the extra mass is muscle or fat, has a higher BMR. Adding muscle raises it. Losing weight lowers it.
2. NEAT (Non-Exercise Activity Thermogenesis) - 15-20%
This is the hidden hero. Walking to the car, fidgeting, standing, doing dishes.
- Sitting through a desk day keeps this component small. A daily walk often changes the total more than a short gym session, because the walk happens on more days.
3. TEF (Thermic Effect of Food) - 10%
Digestion takes energy.
- Protein: Hard to digest. You burn ~20-30% of the protein calories just digesting them.
- Carbs/Fats: Easy to digest (5-10% burn).
- A higher protein intake raises this slice because protein costs more energy to digest than carbohydrate or fat. The effect is real and modest next to the size of the deficit.
4. EAT (Exercise Activity Thermogenesis) - 5-10%
The gym. Surprisingly, this is the smallest component for most people. An hour of weightlifting might only burn 300 calories—equivalent to one bagel. You cannot "out-train" a bad diet.
Calculating Your Numbers
Use the TDEE Calculator. It uses the Mifflin-St Jeor equation (the most accurate standard) modified by an activity multiplier.
The Activity Multiplier Trap: Most people overestimate activity.
- "Moderately Active" (3-5 days/week) usually assumes meaningful cardio.
- If you lift weights 3 times a week but sit in a chair for 50 hours, you are likely "Lightly Active."
Once the activity level is honest, use what TDEE means for a deficit or surplus for the 300–500 calorie adjustments and the two-week scale check. The calculator is the estimate. The scale is the correction.