The One Rule
Every diet that has ever worked — keto, paleo, vegan, intermittent fasting, Weight Watchers — works because of one thing:
You consumed fewer calories than you burned.
That's it. There is no metabolic magic. No "fat-burning foods." No "starvation mode" that makes you gain weight by eating less. (That isn't a thing.)
This is the First Law of Thermodynamics applied to biology. Energy cannot be created or destroyed. If you consume less energy than your body needs, the deficit comes from stored energy (body fat).
Understanding TDEE
Your Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns in a day. It has four components:
1. BMR (Basal Metabolic Rate) — 60-70%
The calories your body burns just being alive. Breathing, pumping blood, maintaining body temperature. Even in a coma, your body burns this much.
2. NEAT (Non-Exercise Activity Thermogenesis) — 15-25%
Everything that isn't "exercise." Walking to the fridge. Fidgeting. Standing up. Taking the stairs.
This is the most variable component and the one most people underestimate. An office worker might burn 200 NEAT calories. A construction worker might burn 1,500.
3. TEF (Thermic Effect of Food) — 5-10%
Digesting food itself costs energy. Protein costs the most to digest (~25% of its calories), carbs are in the middle (~8%), and fat is the cheapest (~2%).