Calorie deficit/surplus

The basic principle: 7,700 kcal = 1 kg of fat

To lose 1 kg of fatty tissue, you must create a cumulative deficit of approximately 7,700 kcal (academic figure: 1 g of fat = 9 kcal, fat mass ≈ 87% pure fat). Over one week, a deficit of 500 kcal/day theoretically leads to −0.45 kg of fat.

Recommended speeds per profile

Weight loss

• Prudent (0.5% of weight/week): comfortable, durable, ideal simultaneously with training. For 70 kg: −350 g/week
• Moderate (0.75%/week): balance speed / muscle preservation. Reference for the majority of protocols. For 70 kg: −525 g/week
• Aggressive (1%/week): quick but costly (fatigue, loss of lean mass if insufficient protein). To be reserved for experienced athletes. For 70 kg: −700 g/week

Gain muscle

• Prudent (0.15%/week): “lean” intake, almost fat-free. Slow but clear. For 70 kg: +105 g/week
• Moderate (0.3%/week): recommended for most intermediates. For 70 kg: +210 g/week
• Aggressive (0.5%/week): rapid onset, less favorable muscle/fat ratio. Suitable for beginners or ectomorphs. For 70 kg: +350 g/week

Why not exceed these thresholds?

Beyond 1% of weight loss per week, you risk:

• Loss of muscle mass (even with high proteins)
• Fall in metabolism (metabolic adaptation)
• Fatigue, reduced performance, sleep problems
• Rebound effect when exiting the deficit

In intake, exceeding 0.5% per week mainly results in fat (muscle builds slowly, max 1-2 kg of muscle per year in an intermediate).

The myth of exact calculation

Estimates are within ±10-15%. Factors that vary the actual speed: metabolic adaptation (your TDEE decreases as you lose it), variation in body water, quality of sleep, stress level. Weekly weighing averaged over 7 days is the most reliable indicator.

When to take a break?

On a long dry period (>8 weeks), plan diet breaks: 7-14 days at maintenance (pure TDEE) to restart the metabolism and provide mental relief. The loss then resumes more quickly. It is validated by the MATADOR protocols (Byrne 2018).