Weight Loss Science Guide

The Fundamental Equation

Weight loss is governed by energy balance: calories consumed vs. calories burned. When you consume fewer calories than you burn (a deficit), your body draws on stored energy (primarily fat) to make up the difference. This is physics, not opinion — it applies to every diet that works.

BMR: Your Metabolic Baseline

Basal Metabolic Rate accounts for 60-75% of your daily calorie burn. It's the energy cost of being alive — heart beating, lungs breathing, cells regenerating. Larger bodies, more muscle mass, younger age, and male sex all increase BMR.

The most accurate BMR formula for most people is Mifflin-St Jeor, validated across multiple studies as having the lowest error rate compared to indirect calorimetry.

TDEE: Your Actual Burn Rate

TDEE adds activity to your BMR. Most people overestimate their activity level. If you have a desk job and exercise 3-4 times per week, you're "lightly active" at best — not "very active."

Why Diets Plateau: Metabolic Adaptation

After 4-8 weeks of caloric restriction, your body fights back. BMR decreases by 5-15% beyond what weight loss alone would predict — a phenomenon called adaptive thermogenesis. You also move less unconsciously (reduced NEAT). This is why weight loss slows over time and why recalculating your targets regularly is essential.

The Role of Protein

During a calorie deficit, adequate protein intake is non-negotiable. Protein preserves lean muscle mass, has the highest thermic effect of food (20-30% of protein calories are burned during digestion), and is the most satiating macronutrient. Research consistently shows that higher protein diets result in more fat loss and less muscle loss during a deficit.