Planning the deficit or the surplus
How fast to lose or gain, why the 7,700 kcal per kilo rule promises dates it cannot keep, and how to split protein, fat and carbohydrate.
With expenditure estimated, the rest is a decision: how far above or below to eat, and for how long. Both questions have evidence-backed answers, and neither answer is "as much as you can stand".
Set a rate, not a percentage
A 20 % deficit means very different things at 55 kg and at 110. What has evidence behind it is not a percentage of calories but a rate of weight change, expressed as a fraction of body weight per week.
Losing slowly preserves lean mass and performance
Garthe's trial in elite athletes compared two rates of loss —roughly 0.7 % and 1.4 % of body weight per week— under the same resistance training. The slow group gained lean mass while losing fat and improved in strength and power; the fast group lost more total weight but also lost lean mass. The ISSN position stand and Helms' contest-prep recommendations put the useful range at 0.5-1 % of body weight per week.
| Goal | Rate | For an 80 kg person |
|---|---|---|
| Lose fat, already lean | 0.25-0.5 %/week | 200-400 g per week |
| Lose fat, general case | 0.5-1 %/week | 400-800 g per week |
| Lose fat, a lot to lose | up to 1.25 %/week | ~1 kg per week, and briefly |
| Build muscle, trained | 0.125-0.25 %/week | 100-200 g per week |
| Build muscle, beginner | up to 0.5 %/week | up to 400 g per week |
Why the gaining numbers are ten times smaller
It isn't caution: it's a biological ceiling. The capacity to build new muscle is measured in hundreds of grams a month in someone already trained. Anything you eat above that ceiling does not become muscle faster; it is stored as fat and lengthens the cut that follows. A big surplus accelerates nothing.
The 7,700 kcal rule and why it fails
From rate to calories is one arithmetic step: a kilo of body tissue is worth about 7,700 kcal (the familiar 3,500 kcal per pound). Losing 0.5 kg a week would be 3,850 kcal a week, roughly 550 a day below expenditure. The calculator does that sum with your weight and your rate.
That rule systematically overestimates loss
The rule assumes expenditure stays put while you shrink, and it does not: a lighter body costs less to move and less to maintain, and on top of that comes adaptive thermogenesis — a drop in expenditure beyond what the lost weight explains. Applied linearly, the rule predicts indefinite losses that never happen. Dynamic models such as Hall's reproduce what actually occurs: a curve flattening towards an equilibrium weight, with time constants on the order of a year.
What that means in practice
Any calculator handing you an exact date —"you'll be 72 kg on 14 March"— is extrapolating a straight line. Real loss decelerates on its own: the same plate that was a deficit in January is maintenance by April. That is why this app draws a curve rather than a line, and why it sometimes tells you that at these calories you will not reach your target. That is not a bug in the maths; it is the answer.
- Don't go below your resting metabolic rate. Eating less than you'd burn lying down, week after week, speeds up adaptation and muscle loss — not fat loss.
- Absolute floor: below ~1,500 kcal (men) or ~1,200 (women) it is very hard to cover vitamins and minerals from ordinary food.
- Revisit every 3-4 weeks. The expenditure you had two months ago is not yours any more.
The split: protein, fat, carbohydrate
The order in which the split is decided is not arbitrary, and understanding it defuses half the arguments about diets.
- 1
Protein first
It's the only macronutrient with a proven floor for keeping and building muscle. Morton's meta-analysis puts the plateau at ~1.6 g/kg/day, with the confidence interval reaching 2.2. In a deficit the high end is the place to be: the ISSN cites 2.3-3.1 g/kg of lean mass for retaining muscle in trained people eating below expenditure. How to spread it across the day is in recovery; if you cover it with powder, which type to pick.
- 2
Fat second
It has a hormonal and functional floor around 0.5 g/kg, and below 20 % of calories the fat-soluble vitamins start to suffer. 25-30 % of calories is a comfortable place to sit.
- 3
Carbohydrate takes what is left
Not because it's leftover, but because it's the adjustable variable: there is no essential requirement for it and it is the fuel for lifting. If something has to give when calories drop, this is it. What you eat during a long effort is a separate matter, counted in grams per hour (eating and drinking on the run).
With calories and protein matched, the rest of the split barely matters
The ISSN position stand on diets and body composition is explicit: once total calories and protein are equated, differences between low-carbohydrate, low-fat and everything in between are small or absent for body composition change. Adherence —which diet you can actually sustain— predicts the outcome better than the split does.
- Protein at maintenance
- 1.6-1.8 g/kg/day
- Protein in a deficit
- 2.0-2.4 g/kg/day
- Fat
- 25-30 % of calories
- Carbohydrate
- The remainder
The harsher the deficit and the leaner you are, the higher.
Never below ~0.5 g/kg.
Prioritise placing it around training.
When weight stalls
Three or four weeks with no movement in the weekly average is a real plateau. Anything shorter is noise. When it arrives, check in this order.
- Are you eating what you think you are? Under-reporting of intake is systematic and large in field studies. Weighing food for a week usually solves the mystery.
- Has your NEAT dropped? In a deficit, spontaneous movement falls without you noticing. Counting steps makes it visible.
- Has your expenditure dropped? You weigh less and have been in a deficit for weeks: recalculate with today's weight. The app does it on its own every time you log a new one.
- Only then, cut calories or add activity. In that order of preference: raise expenditure before trimming further, because the floor on a deficit is real.
Diet breaks are part of the plan
Two-week stretches eating at maintenance, dropped into a long deficit, are standard practice in contest preparation: they buy hormonal and psychological room and make the process sustainable. Almost nobody sustains a nine-month uninterrupted deficit.
This is education, not an individual prescription
If you have a metabolic, cardiovascular or digestive condition, an eating disorder, or you are pregnant or breastfeeding, a healthcare professional should sign off on your intake. Nothing here replaces that conversation.
Takeaways
- Pick a rate (0.5-1 % of body weight per week losing; 0.125-0.25 % gaining), not a deficit percentage.
- The 7,700 kcal/kg rule is fine for starting, useless for predicting dates: loss decelerates on its own.
- Protein first, fat second, carbohydrate with whatever is left.
- Recalculate every 3-4 weeks or whenever your weight changes; two-month-old expenditure is not yours.
Sources for this chapter
- [1]Garthe I, Raastad T, Refsnes PE, Koivisto A, Sundgot-Borgen J (2011). Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. International Journal of Sport Nutrition and Exercise Metabolism. trial
- [2]Helms ER, Aragon AA, Fitschen PJ (2014). Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition. review
- [3]Aragon AA, Schoenfeld BJ, Wildman R, et al. (2017). International society of sports nutrition position stand: diets and body composition. Journal of the International Society of Sports Nutrition. position stand
- [4]Thomas DM, Martin CK, Redman LM, et al. (2013). Why is the 3500 kcal per pound weight loss rule wrong?. International Journal of Obesity. review
- [5]Hall KD, Sacks G, Chandramohan D, et al. (2011). Quantification of the effect of energy imbalance on bodyweight. The Lancet. review
- [6]Rosenbaum M, Leibel RL (2010). Adaptive thermogenesis in humans. International Journal of Obesity. review
- [7]Jäger R, Kerksick CM, Campbell BI, et al. (2017). International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition. position stand
- [8]Morton RW, Murphy KT, McKellar SR, et al. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine. meta-analysis
- [9]National Institute of Diabetes and Digestive and Kidney Diseases (NIH) (2026). Body Weight Planner: simulador del modelo dinámico de Hall. NIDDK. resource