WHAT IS A CALORIE DEFICIT?
A calorie deficit occurs when you consume fewer calories than your body burns. This forces your body to use stored energy (primarily fat) to make up the difference. It's the fundamental principle behind all weight loss—regardless of the diet you follow.
The math is straightforward: 1 kg of body fat contains approximately 7,700 calories. To lose 1 kg per week, you'd need a total deficit of 7,700 calories, or about 1,100 calories per day—which is too aggressive for most people. That's why sustainable weight loss typically targets 0.5-0.75 kg per week.
Understanding Deficit Sizes
Small Deficit (200-300 cal)
Results: 0.2-0.3 kg/week loss
Best for: Those close to goal weight, maintaining muscle while slowly leaning out, or people who struggle with larger deficits. Easiest to sustain long-term.
Moderate Deficit (400-500 cal)
Results: 0.4-0.5 kg/week loss
Best for: Most people. Good balance between speed and sustainability. The standard recommendation for healthy weight loss.
Aggressive Deficit (700-1000 cal)
Results: 0.6-1 kg/week loss
Best for: Those with significant weight to lose, short-term phases (4-8 weeks), or under medical supervision. Requires high protein and careful planning.
The Science of Fat Loss
When you maintain a calorie deficit, your body goes through several adaptations:
Fat Oxidation Increases
Your body increases the rate at which it breaks down stored fat for energy. This is the primary goal of a deficit.
Metabolic Rate Decreases
Your body becomes more efficient, burning fewer calories. This is normal adaptation, not "starvation mode."
Hunger Increases
Hormones like ghrelin increase appetite. This is why high protein and fiber help with satiety.
NEAT Decreases
Non-exercise activity often drops unconsciously. You may move less, fidget less, and feel more tired.
Why Protein is Critical During a Deficit
During a calorie deficit, your body doesn't just burn fat—it can also break down muscle for energy. To minimize muscle loss, you need:
2.0-2.4g
protein per kg bodyweight
30-40g
per meal (3-4 meals)
2-3×
resistance training/week
Research shows that higher protein intakes during a deficit result in significantly more fat loss and less muscle loss compared to lower protein intakes—even with the same calorie deficit.
Common Calorie Deficit Mistakes
Starting Too Aggressive
Large deficits lead to faster adaptation, more muscle loss, and worse adherence. Start moderate and adjust as needed.
Not Tracking Accurately
Studies show people underestimate intake by 30-50%. Use a food scale, track everything, including cooking oils and "bites."
Ignoring Protein
Cutting calories while keeping protein low leads to muscle loss, slower metabolism, and worse body composition.
Expecting Linear Progress
Weight fluctuates due to water, food volume, hormones, etc. Focus on 4-week trends, not daily changes.
Dieting Too Long
Extended deficits cause significant adaptation. Take diet breaks (1-2 weeks at maintenance) every 8-12 weeks.
When to Adjust Your Deficit
Your initial calorie target is just a starting point. Here's when to make adjustments:
| Situation | Action |
|---|---|
| No weight loss for 2-3 weeks (while tracking accurately) | Reduce by 100-150 calories |
| Losing more than 1kg/week consistently | Increase by 100-200 calories |
| Lost 5+ kg or dieting for 8+ weeks | Recalculate TDEE with new weight |
| Constantly hungry, low energy, poor workouts | Consider a 1-2 week diet break at maintenance |
The Minimum Safe Calorie Intake
While creating a deficit is necessary for weight loss, going too low is counterproductive and potentially harmful. General guidelines:
For Women
1,200 cal
Minimum without medical supervision. May need more for active women.
For Men
1,500 cal
Minimum without medical supervision. May need more for active men.
These are general floors. Your actual minimum should never be below your BMR for extended periods, as this can cause significant metabolic adaptation, muscle loss, and nutritional deficiencies.
Frequently Asked Questions
How long should I stay in a deficit?▼
Most experts recommend dieting phases of 8-16 weeks, followed by a 1-2 week maintenance period (diet break). This helps prevent excessive metabolic adaptation and gives your body and mind a break. For significant weight loss, you may need multiple phases.
Will my metabolism slow down permanently?▼
No. Metabolic adaptation is real but temporary. Your metabolism decreases during a deficit and increases when you return to maintenance or a surplus. The key is to lose weight at a reasonable rate, maintain muscle through protein and training, and take periodic diet breaks.
Should I eat back exercise calories?▼
Generally no—your TDEE calculation already accounts for your average activity level. Fitness trackers often overestimate calories burned. However, if you do significantly more activity than usual (long hike, extra workout), adding 100-200 calories is reasonable.
Why did I stop losing weight?▼
Weight loss plateaus happen for several reasons: you've lost weight so your TDEE is lower, metabolic adaptation has occurred, tracking accuracy has slipped, or increased activity is causing water retention. Give it 2-3 weeks of consistent tracking before adjusting calories.
Can I lose fat and build muscle at the same time?▼
Yes, this is called body recomposition. It's most effective for beginners, those returning from a break, or those with higher body fat. It requires eating at a slight deficit or maintenance, very high protein (2g+/kg), and consistent resistance training. Progress is slower but results in better body composition.