TDEE and Fat Loss: How Large Should the Deficit Be?
Fat loss is ultimately an energy deficit, but "eat less" is only one lever. The sustainable approach is to estimate daily expenditure first, then set the deficit and protein intake.
BMR versus TDEE
BMR is the minimum energy to sustain life at rest; TDEE = BMR × activity factor, covering walking, work, exercise and the thermic effect of food.
The Mifflin-St Jeor equation estimates BMR: men 10×kg + 6.25×cm − 5×age + 5; women end with −161. Activity factors run from 1.2 (sedentary) to 1.725 (very active).
Sizing the deficit
About 7,700 kcal ≈ 1 kg of fat. A 500 kcal daily deficit implies ~0.45 kg per week, though metabolic adaptation and reduced spontaneous activity slow it in practice.
Start at 15%–20% below TDEE, not a 40% cut. Aggressive deficits drive muscle loss, fatigue and rebound binge eating. Leaner people should use smaller deficits.
Why protein matters
In a deficit, low protein accelerates muscle loss. A common target is 1.6–2.0 g per kg of body weight, paired with resistance training. Protein also improves satiety, which helps adherence.
Do not push fat too low (hormones and fat-soluble vitamins), and allocate carbs around training and personal preference.
Handling a plateau
If weight is flat for two weeks, check three things: under-reported intake (oils, drinks, snacks), reduced daily movement, and metabolic adaptation.
The usual fix is to recalibrate tracking for 1–2 weeks before cutting further — or add steps and training volume instead of eating less.
Important caveat
All of the above are estimates; individual variation can reach ±10%–15%. With thyroid, diabetes or kidney conditions, or during pregnancy/lactation, consult a clinician or registered dietitian rather than applying these numbers directly.
This article provides general information and calculation methods only. It is not medical, investment or legal advice; consult a qualified professional for your situation.