Surplus and Deficit: How to Do It Well
Introduction
Almost everyone wanting to change their body composition makes the same error, in both directions: they go too fast. Aggressive deficits that sacrifice muscle, generous surpluses that sacrifice little more than the waistline.
Speed isn't a stylistic detail: it determines what proportion of the change is fat and what proportion is muscle.
The question isn't how much you want to change. It's how much muscle you're willing to lose for going fast.
The deficit: speed decides composition
Garthe and colleagues' study compared two rates of weight loss in athletes: a slow one — around 0.7 % of body weight per week — and a fast one, near 1.4 %. Both groups lost fat. The difference was in muscle: the slow group preserved and even gained lean mass; the fast one lost it.
Hence the range in use today:
- 0.5 to 1 % of body weight per week. For 80 kg, that's 400 to 800 grams weekly.
- Slower if you're already lean. Faster only if you have substantial fat to lose, and for short periods.
And three things make that deficit preserve muscle rather than spend it:
High protein. Requirements rise in a deficit: figures of 1.8 to 2.4 g per kilo are used, toward the top the leaner you are.
Strength training. It's the signal telling the body the muscle is needed. Without it, much of the loss is lean mass.
Not cutting everything. A deficit of 300 to 500 kcal is enough. Deficits of 1,000 kcal don't accelerate proportionally and do increase the cost.
The surplus: less than you think
Here the error runs the other way and is equally common. The intuitive logic — "if I eat a lot, I gain a lot of muscle" — fails because the rate at which muscle can be built has a physiological ceiling, and everything above that gets stored as fat.
Reasonable rates:
- 0.25 to 0.5 % of body weight per week. For 80 kg, 200 to 400 grams weekly.
- Toward the top if you've trained for a short time; toward the bottom if you've trained for years.
That corresponds to a modest surplus, on the order of 200 to 350 kcal daily. Studies comparing larger surpluses find more weight gain and no more muscle gain: the difference was fat.
And a consequence almost nobody mentions: every extra kilo of fat gained in a bulking phase is an additional month of deficit afterward.
Metabolic adaptation
It's real and usually exaggerated.
When you lose weight, energy expenditure falls more than your new size alone would explain: spontaneous activity, resting expenditure and some hormonal signals all drop. That phenomenon exists, is well documented, and is why a deficit that was working stops working.
What it isn't: a "starvation mode" preventing fat loss. The magnitude is modest and largely reversible on returning to maintenance.
The practical consequence: deficits work better in blocks. Eight to sixteen weeks of deficit, then several weeks at maintenance, and another block if needed. That intermittent structure shows better fat-loss results than continuous restriction in some trials, besides being considerably more sustainable.
How to know you're on track
In a deficit:
- Weekly average weight falls within the expected range.
- Strength holds or drops very little.
- Waist circumference falls.
- If strength collapses and weight drops fast, you're being too aggressive.
In a surplus:
- Weekly average weight rises slowly.
- The waist rises far less than the weight.
- Weights in your log go up.
- If the waist rises at the same rate as weight, your surplus is too large.
In both cases the scale alone isn't enough: cross-reference with waist and with your training log.
When to be in each phase
A sensible structure for an intermediate who doesn't compete:
- Most of the year at maintenance, training and progressing.
- Deficit blocks when you want to lose fat, eight to sixteen weeks.
- Light surplus blocks when you want to prioritize gain, three to six months.
Being permanently in one of the two phases is what produces the stories of people who've been "on a diet" for years without changing.
Common mistakes
Aggressive deficits "because I'm in a hurry". They cost muscle, performance and adherence.
Generous surpluses "because I'm bulking". They end in a deficit longer than the one you saved.
Lowering protein in a deficit. That's when it's most needed.
Stopping strength training while losing weight. It's what turns weight loss into muscle loss.
Switching phases every three weeks. Neither one achieves anything.
A note
If losing weight occupies a significant share of your daily attention, if binges appear, marked guilt after eating, or if the cycle of deficit and regain has repeated for years, it's worth discussing with a professional. The problem in those cases isn't calorie arithmetic.
Conclusion
In both directions, the error is haste. Half to one percent of body weight per week to lose, a quarter to half a percent to gain, high protein and strength training in both cases.
Define your target rate in kilos per week today and write it down. Then, for three weeks, compare your weekly average weight against that number — not against the ideal in your head. Adjusting the speed is the only change that decides whether the result is muscle or just weight.
References
- Garthe, I., et al. (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, 21(2).
- Longland, T. M., et al. (2016). Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss. The American Journal of Clinical Nutrition, 103(3).
- Byrne, N. M., et al. (2018). Intermittent energy restriction improves weight loss efficiency in obese men: The MATADOR study. International Journal of Obesity, 42(2).
- Trexler, E. T., Smith-Ryan, A. E., & Norton, L. E. (2014). Metabolic adaptation to weight loss: Implications for the athlete. Journal of the International Society of Sports Nutrition, 11.
- Slater, G. J., et al. (2019). Is an energy surplus required to maximize skeletal muscle hypertrophy associated with resistance training? Frontiers in Nutrition, 6.