In This Article
Key Takeaways
- A 3,500 kcal deficit ≈ 1 pound of fat lost (the classic rule — actual results vary by individual)
- A 300–500 kcal/day deficit is sustainable; it targets 0.5–1 lb/week of fat loss
- High protein (0.7–1.0g/lb body weight) is the most important variable for muscle preservation
- Resistance training during a deficit dramatically reduces muscle loss
- TDEE decreases as you lose weight — recalculate every 10–15 lbs lost
The Math Behind Fat Loss
One pound of body fat contains approximately 3,500 kcal of stored energy. To lose 1 pound per week, you need a cumulative deficit of 3,500 kcal over 7 days — or about 500 kcal/day below your maintenance level.
This is a useful starting model, but it's an approximation. Actual fat loss depends on body composition changes, hormonal adaptation, and changes in unconscious movement. Expect real-world results of 0.5–1.0 lb/week for most people with a 300–500 kcal daily deficit.
What is TDEE? Total Daily Energy Expenditure is the total number of calories your body burns per day, including basal metabolism, digestion, physical activity, and unconscious movement (NEAT). Your TDEE is your maintenance calorie level — eat below it and you lose weight; eat above and you gain.
Step 1: Calculate Your TDEE
The Mifflin-St Jeor equation is the most accurate commonly-used formula for estimating BMR (basal metabolic rate):
Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161
Then multiply by your activity factor to get TDEE:
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | × 1.2 | Desk job, minimal movement |
| Lightly active | × 1.375 | Light exercise 1–3 days/week |
| Moderately active | × 1.55 | Moderate exercise 3–5 days/week |
| Very active | × 1.725 | Hard exercise 6–7 days/week |
| Extremely active | × 1.9 | Physical job + daily training |
Calculate Your TDEE Automatically
Enter your stats once — get your maintenance calories and suggested deficit targets.
Step 2: Set Your Deficit
| Deficit Size | Daily Reduction | Expected Rate | Best For |
|---|---|---|---|
| Conservative | −200–300 kcal | ~0.25–0.5 lb/week | Lean individuals, minimal muscle loss priority |
| Moderate | −300–500 kcal | ~0.5–1.0 lb/week | Most people — best balance of speed and sustainability |
| Aggressive | −500–750 kcal | ~1.0–1.5 lb/week | Those with more to lose; higher muscle loss risk |
| Very aggressive | −750–1000 kcal | ~1.5–2.0 lb/week | Medical supervision recommended |
A common mistake is setting too large a deficit too soon. Aggressive deficits increase cortisol, reduce testosterone, impair recovery, cause greater muscle loss, and are difficult to sustain. Start moderate and adjust based on actual progress over 2–4 weeks.
Minimum Calorie Floor
Regardless of deficit size, most dietitians recommend not dropping below 1,200 kcal/day for women or 1,500 kcal/day for men without medical supervision. Below these levels, it becomes very difficult to meet protein and micronutrient needs.
Step 3: Prioritize Protein
High protein intake is the single most important dietary variable during a fat loss phase. It:
- Preserves lean muscle mass (muscle is metabolically expensive; your body protects it when protein is abundant)
- Increases satiety — protein is more filling per calorie than carbs or fat
- Has the highest thermic effect (~25–30% of protein calories are burned in digestion)
- Prevents "skinny fat" outcomes where weight drops but body composition worsens
| Goal | Protein Target |
|---|---|
| General weight loss (sedentary) | 0.6–0.8g per lb body weight |
| Weight loss + exercise | 0.8–1.0g per lb body weight |
| Lean bulk (gaining muscle) | 0.7–1.0g per lb body weight |
| Body recomposition | 1.0–1.2g per lb body weight |
For a 180 lb person in a fat loss phase with regular exercise, that's 144–180g of protein per day — hitting that target should be your first nutrition priority each day.
Step 4: Use Activity to Your Advantage
You can create a deficit by eating less, moving more, or both. A combination is usually best because it avoids eating so little that nutrition suffers, and avoids such high exercise volume that recovery is impaired.
Resistance Training During a Deficit
Resistance training sends the signal to preserve muscle tissue even when calories are restricted. Studies consistently show that people who combine a moderate deficit with resistance training lose almost exclusively fat, while those who diet without lifting lose a significant proportion of muscle mass along with fat.
NEAT: The Underrated Factor
Non-exercise activity thermogenesis (NEAT) — fidgeting, walking, standing, cooking, cleaning — can account for 300–500 kcal/day difference between individuals. Increasing daily steps from 5,000 to 10,000 burns an extra 200–400 kcal/day, equivalent to a meaningful portion of a moderate deficit.
Why Plateaus Happen & How to Break Them
Metabolic Adaptation
As you lose weight, three things happen that reduce your TDEE:
- Smaller body = lower BMR — a 30 lb lighter version of you burns fewer calories at rest
- Reduced NEAT — unconsciously, you move less when in a deficit (energy conservation)
- Increased metabolic efficiency — muscle fiber type shifts and mitochondrial function changes
The practical fix: recalculate your TDEE every time you lose 10–15 lbs and reduce your calorie target accordingly. What was a 500 kcal deficit at 200 lbs may be only a 200 kcal deficit at 185 lbs.
Calorie Creep
Research consistently shows people underestimate their calorie intake by 20–50%, including dieters. If your weight has stalled, try tracking food precisely (weighing solids, measuring liquids) for 1–2 weeks to identify where hidden calories are entering.
Diet Breaks and Refeeds
Planned diet breaks (1–2 weeks at maintenance calories) and periodic refeed days (1 day/week at or near maintenance) can partially reverse metabolic adaptation, restore leptin levels, and improve adherence by preventing diet fatigue. Evidence for the metabolic benefits is moderate; the adherence benefit is clear.
Frequently Asked Questions
A deficit of 300–500 kcal/day (targeting ~0.5–1 lb/week of fat loss) is ideal for most people. Larger deficits (500–750 kcal/day) can work for those with significant weight to lose but increase muscle loss risk and are harder to sustain. Deficits over 1,000 kcal/day are generally not recommended without medical supervision, as they risk nutritional deficiency and significant lean mass loss.
Several factors cause plateaus: metabolic adaptation (BMR decreases as you lose weight and body mass), reduced NEAT (unconscious movement decreases when in an energy deficit), and increased caloric efficiency. The fix is recalculating your TDEE at your new weight and reducing intake or increasing activity to restore the deficit. Also rule out calorie creep — underestimating intake is the most common culprit.
Some muscle loss is possible during a deficit, but it can be minimized with high protein intake (0.7–1.0g/lb body weight) and resistance training. Studies show that combining a moderate deficit with these two factors preserves nearly all lean mass while losing fat. Aggressive deficits, low protein, and no resistance training are the primary causes of unwanted muscle loss.
Neither matters significantly for fat loss specifically — total calorie deficit drives weight loss. Protein should stay high regardless. Whether you reduce carbs or fat depends on personal preference and satiety. Low-carb approaches often produce faster initial weight loss (mostly glycogen and water weight), but long-term fat loss outcomes are similar when total calories and protein are matched.