Where the 7700 kcal/kg number comes from (and why it’s a model, not a law)
Adipose tissue stores about 7700 kcal of usable energy per kilogram (corresponding to 3500 kcal/lb — Wishnofsky 1958). Real-world weight loss in the first 1–2 weeks of a deficit typically runs faster than this constant predicts because glycogen stores release water as they deplete. After about 6 weeks, weight loss slows as your body adapts: NEAT (non-exercise activity thermogenesis) drops, leptin falls, hunger hormones rise. Both effects mean the linear math above is a rough plan, not a guarantee.
What rate is sustainable?
Most clinical guidelines (Obesity Canada, Canadian Adult Obesity Clinical Practice Guidelines, Diabetes Canada) point to 0.25–1 kg/week as the sustainable band. People with a higher starting BMI can sustain the upper end of that range; leaner individuals and athletes generally lose better at 0.25–0.5 kg/week. Going faster usually means losing muscle and fast regain.
Floors that exist for good reasons
1200 kcal/day for women and 1500 kcal/day for men are the conventional “no-supervision” floors below which protein, micronutrient and gallstone risks rise sharply. Very-low- calorie diets (VLCDs, < 800 kcal/day) work and are sometimes used for pre-bariatric weight loss, but they require physician monitoring and a complete-meal-replacement formulation; they aren’t a DIY tool.
Tracking that actually works
Use a 4-week rolling average of weight, not a single weigh-in. Track at the same time of day, in the same clothes, after using the bathroom. Take a tape-measure waist circumference once a week — it usually moves more predictably than the scale because it bypasses water weight.
Sources
- Wadden TA et al. Lifestyle modification for obesity. Circulation. 2012;125:1157-70.
- Obesity Canada. Adult Obesity Clinical Practice Guidelines, 2020 update.
- Health Canada. Healthy Eating and the Canada Food Guide.