The Fundamental Science of Weight Loss
At its core, weight management is governed by the laws of thermodynamics. To lose weight, you must create a calorie deficit—meaning you consume fewer calories than your body burns in a day.
When your body does not get enough external energy from food, it begins breaking down stored body fat and muscle tissue to fuel its metabolic needs. Finding your exact deficit range is the only reliable way to achieve consistent weight loss.
Step 1: Calculate Your TDEE
Your Total Daily Energy Expenditure (TDEE) is the total number of calories you burn per day. It is determined by adding your Basal Metabolic Rate (BMR) to your physical activity level. Doctors typically use the Mifflin-St Jeor formula to estimate this baseline.
Once you know your TDEE, you can subtract calories to create your deficit.
| Deficit Level | Calories Subtracted | Weekly Weight Loss Target |
|---|---|---|
| Mild Deficit | 250 kcal / day | 0.5 lbs (0.2 kg) per week |
| Moderate Deficit | 500 kcal / day | 1.0 lbs (0.5 kg) per week |
| Severe Deficit | 1,000 kcal / day | 2.0 lbs (0.9 kg) per week (Max Recommended) |
Healthy and Sustainable Targets
Creating too large of a deficit (e.g. cutting 1,500+ calories) is counterproductive. It triggers adaptive thermogenesis (often called starvation mode), where your metabolism slows down, and you lose muscle mass instead of fat.
For long-term success, focus on a moderate 500-calorie deficit, pair it with progressive resistance training, and aim to consume at least 1.6 to 2.2 grams of protein per kilogram of body weight to preserve lean muscle.
Try the Live How to Calculate Your Calorie Deficit for Weight Loss (2026 Guide)
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