What is a Calorie Deficit? The Core Principle of Weight Loss

While there are countless diet methods, the foundation of all weight loss is just one thing: Calorie Deficit. By understanding this simple yet powerful principle, you can achieve effective and sustainable weight loss.

Definition

A Calorie Deficit is a state where calories consumed are less than calories burned. In other words, you consume less than you expend.

Formula

Calorie Deficit = Calories Burned - Calories Consumed

Example

• Daily Calories Burned: 2,500kcal
• Daily Calories Consumed: 2,000kcal
• Calorie Deficit: 500kcal

This 500kcal deficit accumulates daily, creating a 3,500kcal deficit per week, which leads to approximately 0.5kg of fat loss.

Scientific Principles of Weight Loss

Energy Balance Equation

Weight Gain

• Calories Consumed > Calories Burned
• Excess energy stored as fat

Weight Maintenance

• Calories Consumed = Calories Burned
• Energy balance state

Weight Loss

• Calories Consumed < Calories Burned
• Stored fat used as energy

Fat 1kg = 7,700kcal

Scientifically, burning 1kg of fat requires approximately 7,700kcal of deficit.

Calculation Examples

Daily 500kcal Deficit

• 1 week: 500 × 7 = 3,500kcal = 0.45kg loss
• 1 month: 500 × 30 = 15,000kcal = 1.95kg loss
• 3 months: About 6kg loss

Daily 700kcal Deficit

• 1 week: 0.64kg loss
• 1 month: 2.7kg loss
• 3 months: About 8kg loss

Calorie Expenditure Composition

1. BMR (Basal Metabolic Rate) - 60-75%

Basal Metabolic Rate: Calories burned doing nothing

• Breathing, heart rate, body temperature maintenance
• Cellular activity, organ functions

Rough Calculation

• Men: Weight(kg) × 24kcal
• Women: Weight(kg) × 22kcal

Examples

• 70kg Male: 70 × 24 = 1,680kcal
• 55kg Female: 55 × 22 = 1,210kcal

2. NEAT (Non-Exercise Activity Thermogenesis) - 15-30%

Non-Exercise Activity Thermogenesis: Daily non-exercise activities

• Walking, standing, climbing stairs
• Housework, office tasks
• Body movements (fidgeting)

Large Individual Variations

• Office job: Low
• Service/construction jobs: High

3. TEF (Thermic Effect of Food) - 10%

Energy required for digestion

• Protein: 20-30% of calories consumed
• Carbohydrates: 5-10% consumed
• Fat: 0-3% consumed

This is why high-protein diets are beneficial for dieting!

4. EAT (Exercise) - 5-10%

Exercise Activity Thermogenesis: Planned exercise

• Gym, running, swimming
• Surprisingly small proportion

TDEE (Total Daily Energy Expenditure)

Total Daily Energy Expenditure

TDEE = BMR × Activity Factor

Activity Factor

• Almost no activity (sedentary): × 1.2
• Light activity (exercise 1-3 times/week): × 1.375
• Moderate activity (exercise 3-5 times/week): × 1.55
• Very active (exercise 6-7 times/week): × 1.725
• Extremely active (2x daily exercise, physical labor): × 1.9

Example: 70kg male, office job, exercises 3 times/week

• BMR: 1,680kcal
• TDEE: 1,680 × 1.55 = 2,604kcal

How to Calculate Calorie Deficit

Step 1: Calculate TDEE

Use Online Calculator (Easiest method)

• Search "TDEE Calculator"
• Enter age, gender, weight, height, activity level

Use Formula (Direct calculation)

Mifflin-St Jeor Formula (Most accurate)

Men

BMR = (10 × Weight kg) + (6.25 × Height cm) - (5 × Age) + 5

Women

BMR = (10 × Weight kg) + (6.25 × Height cm) - (5 × Age) - 161

Then multiply by activity factor to calculate TDEE

Example: 30-year-old woman, 165cm, 65kg, exercises 3 times/week

• BMR = (10 × 65) + (6.25 × 165) - (5 × 30) - 161
• BMR = 650 + 1,031 - 150 - 161 = 1,370kcal
• TDEE = 1,370 × 1.55 = 2,124kcal

Step 2: Determine Deficit Size

Recommended Deficit

Goal	Deficit Size	Weekly Loss
Slow Loss (Sustainable)	250-300kcal	0.25kg
Moderate Loss (Recommended)	500kcal	0.5kg
Fast Loss	700-750kcal	0.75kg
Very Fast Loss (Caution)	1,000kcal	1kg

Warning: Deficit over 1,000kcal not recommended

• Muscle loss
• Metabolic slowdown
• Nutritional deficiency
• Yo-yo effect risk

Step 3: Set Target Calories

TDEE - Deficit = Target Calories

Example (Woman above)

• TDEE: 2,124kcal
• Deficit: 500kcal
• Target Calories: 1,624kcal/day

Step 4: Confirm Minimum Calories

Absolute Minimum

• Women: 1,200kcal
• Men: 1,500kcal

Going below this:

• Metabolic slowdown
• Muscle loss
• Nutritional deficiency
• Fatigue, dizziness
• Hormonal imbalance

Methods to Create Calorie Deficit

Method 1: Diet Adjustment (Most Effective)

Reduce Calorie Intake

Small Changes to Reduce 500kcal

• Morning bagel (300kcal) → 2 eggs + vegetables (150kcal) = -150kcal
• Lunch soda (200kcal) → Water (0kcal) = -200kcal
• Dinner 1.5 rice servings (450kcal) → 1 serving (300kcal) = -150kcal
• Total -500kcal

Replace High-Calorie Foods

• Latte → Americano (-150kcal)
• Fried food → Baked food (-200-300kcal)
• Snacks → Fruits (-100-200kcal)
• Dressing-heavy salad → Balsamic vinegar (-150kcal)

Method 2: Exercise (Supplementary)

Increase Calorie Expenditure

Cardio (Calorie Burning)

• Running 1 hour: 600-800kcal
• Cycling 1 hour: 400-600kcal
• Swimming 1 hour: 500-700kcal
• Brisk walking 1 hour: 300-400kcal

Strength Training (Metabolism Increase)

• Calories during exercise: Low (200-300kcal/hour)
• But muscle gain → BMR increase
• 1kg muscle = 13kcal additional daily consumption

Difficulty of Burning 500kcal by Exercise Only

• Requires 1-hour running
• Hard to maintain daily
• Compensation psychology (eating more after exercise)

Method 3: Combination (Most Effective)

Diet + Exercise

Example: 500kcal Deficit

• Diet adjustment: -300kcal (small changes)
• Exercise: -200kcal (30 min running or 1-hour walk)
• Total -500kcal

Benefits

• Sustainable
• Muscle preservation
• Health improvement
• Stress relief

Creating Deficit Without Calorie Counting

If perfect calorie calculation is difficult:

Method 1: Plate Method

Plate Composition Each Meal

• 1/2: Vegetables (salad, broccoli)
• 1/4: Protein (meat, fish, eggs)
• 1/4: Carbohydrates (rice, sweet potato, whole grains)

Result: Natural calorie reduction, nutritional balance

Method 2: Hand Measurement

Single Serving

• Protein: Palm-sized, thickness
• Carbohydrates: Fist-sized
• Fat: Thumb-sized
• Vegetables: Two hands full

Method 3: Small Habit Changes

Daily Practice

• Over 2L water daily
• Eat vegetables first
• Chew slowly (over 20 minutes)
• Use smaller plates
• Stop late-night eating
• Reduce processed foods
• Avoid sugary drinks

Result: Natural calorie reduction (300-500kcal daily)

Method 4: 80% Rule

• Don't eat until completely full
• Stop at 80% fullness
• Reassess after 20 minutes

Method 5: Weekly Assessment

Weigh at Same Time Weekly

• Decrease: Continue
• Stagnant: Adjust slightly
• Increase: Re-evaluate intake

Common Calorie Deficit Mistakes

Mistake 1: Excessive Deficit

Problem: Over 1,000kcal deficit Results

• Metabolic slowdown ("Starvation mode")
• Muscle loss
• Fatigue, dizziness
• Binge eating possibility

Solution: Maintain 500-750kcal deficit

Mistake 2: Ignoring Nutrition

Problem: 1,500kcal of snacks and instant noodles Results

• Nutritional deficiency
• Hunger
• Muscle loss
• Health deterioration

Solution: Fill calories with nutritious foods

Mistake 3: Weekend Binge

Problem: Good during weekdays, binge on weekends Calculation

• Weekdays (Mon-Fri): -500kcal × 5 = -2,500kcal
• Weekends (Sat-Sun): +1,000kcal × 2 = +2,000kcal
• Weekly Total Deficit: -500kcal

Result: Only 0.3kg loss per month

Solution: Maintain 80% discipline on weekends

Mistake 4: Overestimating Exercise Calories

Problem: Trusting treadmill "600kcal burned" and adding snacks Reality: Actually 400kcal burned

Solution: Trust only 70% of exercise calories

Mistake 5: Overlooking Beverage Calories

Easy to Overlook Drinks

• Latte (tall): 200-300kcal
• Soda: 150-200kcal
• Juice: 120-180kcal
• Alcohol: Beer 1 glass 150kcal, Soju 1 glass 60kcal

Solution: Water, black coffee, unsweetened tea

Mistake 6: Not Maintaining Deficit

Problem: Quit after a few days Result: Weight loss failure

Solution

• Realistic goal (0.5kg/week)
• 80/20 principle (80% strict, 20% flexible)
• Long-term thinking

Overcoming Plateau

What is a Plateau?

No weight change for 2-4 weeks

Causes

1. Metabolic Adaptation: Body adapts to low calories
2. Muscle Gain: Fat reduction, muscle increase (same weight)
3. Water Fluctuation: Fat reduced, water increased
4. Calorie Calculation Error: Not actually in deficit

Overcoming Methods

1. Recalculate

• Recalculate TDEE with current weight
• Weight loss → TDEE reduction → Readjust deficit

Example

• Start: 70kg, TDEE 2,500kcal, Goal 2,000kcal
• 6 weeks later: 65kg, TDEE 2,350kcal, Goal 1,850kcal

2. Refeed Day

• High carbohydrate intake once a week
• Metabolic reboot
• Psychological satisfaction

3. Diet Break

• 1-2 weeks at maintenance calories (TDEE)
• Metabolic recovery
• Restart

4. Exercise Change

• Increase strength training intensity
• Add HIIT
• Increase NEAT (walk more)

5. Precise Calorie Tracking

• Weigh food
• Record everything
• Include sauces, oils, snacks

Preventing Muscle Loss

Risk of muscle loss during calorie deficit.

1. Sufficient Protein

Intake: 1.8-2.5g per kg body weight

• 70kg: 126-175g/day

Effects

• Muscle preservation
• Satiety
• High TEF (calorie consumption)

2. Maintain Strength Training

• 3-4 weight training sessions/week
• Maintain intensity (don't reduce weight)
• "Use it or lose it"

3. Moderate Deficit

• Maintain 500-750kcal deficit
• Avoid over 1,000kcal

4. Sufficient Sleep

• 7-9 hours
• Sleep deprivation → Increased muscle loss

Frequently Asked Questions

Q: Will I lose weight if I just hit calorie targets?

A: Theoretically yes, but nutrition matters. Filling 1,500kcal with pizza and ice cream:

• Extreme hunger (low satiety)
• Muscle loss (protein deficiency)
• Nutritional deficiency (vitamins, minerals)
• Unsustainable
• Health deterioration

"Calories are the king of weight loss, but nutrition is the queen of health". Fill calories with whole grains, protein, vegetables.

Q: Why am I not losing weight despite calorie deficit?

A: Multiple reasons:

1. Not Actually in Deficit: Calorie calculation error (over 70% underestimate)
2. Water Fluctuation: Carbs, salt, menstrual cycle increase water (fat reduces, weight same)
3. Muscle Gain: Muscle increase from exercise, fat reduction (weight maintained, body changes)
4. Not Enough Time: 1-2 weeks is short, wait 4 weeks

Solution: Evaluate with measuring tape, photos, clothing fit, not just weight.

Q: Is Intermittent Fasting Just a Calorie Deficit?

A: Exactly! Intermittent fasting is a tool to create calorie deficit. Limiting meal times naturally reduces calorie intake. But if you binge during eating periods, no deficit occurs. Deficit is key, method is the tool.

Q: Low Carb vs Low Fat, Which is More Effective?

A: Similar if calorie deficit is equal. Research shows:

• Low Carb Diet: Average 7kg loss after 12 months
• Low Fat Diet: Average 7.5kg loss after 12 months
• No significant difference

Important is choosing a method suitable for you and maintaining it long-term. Sustainability > Diet trends.

Q: How to Weigh with Menstrual Cycle Variations?

A: Consistency is key. Recommendations:

• Right after period (lowest weight)
• Same day, same time weekly
• Morning, after bathroom, before meals
• Track 4-week average

Don't worry about 1-3kg increase before period - it's water. Look at long-term trend.

Q: How Much Weight Can I Lose with Calorie Deficit?

A: Theoretically unlimited, but practical staged approach needed:

• Over 10kg loss: 2-4 week maintenance every 5kg
• Prevent metabolic adaptation
• Psychological recharge

Target Weight = Height(cm) - 110 (men) or - 115 (women) is healthy range. Maintain BMI 18.5-24.9.

Conclusion

Calorie deficit is the common denominator of all diets. Low carb, intermittent fasting, keto, paleo... all ultimately create a calorie deficit. Don't be misled by complex diet methods, understand this basic principle.

Successful Weight Loss Formula

1. Calculate TDEE (online calculator)
2. Set 500kcal Deficit (0.5kg loss/week)
3. Nutritious Foods (protein, vegetables, whole grains)
4. Add Exercise (strength + cardio)
5. Maintain Consistency (80/20 principle)
6. Reassess and Adjust every 4 weeks

It doesn't have to be perfect. 80% adherence is sufficient. The key is not an extreme short-term diet, but creating lifelong sustainable healthy habits.

Start calculating your TDEE today and create a 500kcal deficit with small changes. In three months, you'll meet a 6kg lighter version of yourself!