Fat loss is one equation: energy balance, deficit size and patience

Guides · Fat loss

Strip away the diets with names, the "one weird trick" videos and the supplement aisle, and fat loss comes down to a single idea: over time, you have to spend a little more energy than you take in. That's it — that's the whole equation. Everything else in this guide is really about the three things that decide whether that simple equation actually works for you: how big a gap to run, how fast to expect the scale to move, and how much patience the process needs when the numbers stall.

This is a deliberately deep, evergreen guide rather than a marketing piece. We'll build up the science carefully, correct the myths that make people quit a plan that was working, and finish with a worked example that puts a sensible deficit and a crash diet side by side so you can see exactly what you trade away by rushing. Where a number is genuinely textbook-established we'll give it — always as an estimate, never as a promise — and where the honest answer is "it varies," we'll say so.

1. The one equation: energy balance

Fat loss is governed by energy balance — the difference between the energy you take in from food and drink and the energy your body spends over a period of time. Run a gap on the spending side often enough (a deficit), and your body makes up the shortfall from its own stores. Over weeks and months, and with the right supporting habits, most of what it draws down is body fat. This is an application of a physical law — energy is conserved — and body-weight change follows from the imbalance between energy in and energy out, however hard those two sides are to measure.^[1] Every genuinely effective approach to fat loss, whatever it's called, works by creating this gap; the names and rules are just different routes to the same equation.

What "energy out" is actually made of

"Burn" isn't one number — it's the sum of several, and knowing the parts explains almost everything that follows:

• Resting metabolic rate (RMR, sometimes BMR) — the energy just to keep you alive at rest. For most people this is the largest slice of the total, at roughly two-thirds of energy out.^[1] It's closely tied to how much fat-free mass you carry: pooling 213 adults, fat-free mass on its own explained about 73% of the variance in resting energy expenditure.^[2]
• The thermic effect of food (TEF) — the energy spent digesting and processing what you eat. On a mixed diet eaten at energy balance it comes to about 10% of the energy taken in over 24 hours.^[3] Reported values for a mixed diet span roughly 5–15%, and differ by nutrient: 0–3% for fat, 5–10% for carbohydrate and 20–30% for protein.^[4]
• Movement — both deliberate exercise and NEAT, the non-exercise activity of ordinary life: walking, standing, fidgeting, posture. Activity is the most variable component of daily energy expenditure.^[3] NEAT alone can differ by as much as 2,000 kcal a day between two adults of similar body size, lean mass, age and sex.^[5]

Two consequences matter for fat loss. First, because RMR dominates, most of your daily burn happens whether or not you train — exercise adds to the total and brings large independent health benefits, but you cannot reliably out-train an intake that's simply too high. Second, "energy out" is not a fixed dial: it drifts with your body size, your activity and how your body responds to eating less. That's why the equation is simple but the arithmetic is slippery — a theme we return to in section 4.

2. How big a deficit to run

Once you accept that a deficit is the lever, the obvious question is how big. To size one, it helps to have a rough conversion between energy and body mass. The textbook rule of thumb is that about 7,700 kcal is roughly 1 kg of body-weight change — it began life as a 1958 review concluding that the caloric equivalent of one pound of body weight gained or lost is 3,500 kcal.^[6] That figure was motivated by the calculation that a pound of adipose tissue stores approximately 3,500 kcal.^[7]

Treat that number as a planning estimate, not a law. Its most serious error is that it is a static model: it treats the energy imbalance as a fixed quantity when in reality that imbalance changes throughout a diet, which is why it leads to overestimation of weight loss in individuals and populations.^[7] Use it to point yourself in a direction and set a pace — then let your actual weight trend, not the arithmetic, tell you what's really happening.

A sensible range, not a single answer

Rather than picking a fixed calorie cut, it's more robust to size the deficit relative to your own maintenance level — and to steer by the rate of loss rather than the size of the cut. The clearest trial on the question randomised 24 elite athletes, all doing four resistance sessions a week, to lose either 0.7% or 1.4% of body weight a week; energy intake was reduced by 19% and 30% respectively. Both groups lost about the same body weight, but the slower group increased lean body mass by 2.1% while the faster group's was unchanged, and the slower group shed 31% of its fat mass against 21% in the faster group.^[8] That fits a longer-standing observation: as energy intake is reduced further, lean tissue makes up an increasing fraction of the total weight lost, and that lean fraction is larger in leaner people to begin with — so those with less body fat have most to gain from a gentler cut.^[9] The practical rule that falls out of both is to use the smallest deficit that yields appreciable weight loss.^[10]

In everyday terms, holding the gentler end of that pace works out at somewhere around 300–500 kcal a day for people of ordinary body weight, if you convert at roughly 7,700 kcal per kilogram^[6] — enough to move the scale steadily without wrecking training, recovery or adherence.

The single most important principle here is counter-intuitive: the best deficit is the one you can actually sustain, not the biggest one you can bear for a fortnight. A moderate gap you can hold for months, while training and recovering well, routinely produces more total fat loss than an aggressive one you abandon — a point we make concrete in the worked example.

3. A realistic rate of loss

With a sensible deficit set, what should the scale actually do? A widely cited, evidence-informed target for fat loss is roughly 0.5–1% of body weight per week — the figure recommended for natural bodybuilders preparing for competition, where calorie intake is set at a level producing body-weight losses of approximately 0.5–1% a week to maximise muscle retention^[11] and repeated in the position stand on diets and body composition of the International Society of Sports Nutrition (ISSN, a United States-based professional society with international membership).^[12] National dietetic guidance puts the same idea in absolute terms: the British Dietetic Association (United Kingdom) calls 0.5–1 kg a week, or 5–10% of body weight over three to six months, a realistic target.^[13] The percentage version deliberately scales to the person: a heavier body can lose more in absolute terms at the same percentage, while a lighter or leaner person should aim toward the gentler end to protect muscle — reviews written for physique athletes lean toward 0.5% a week or slower for exactly that reason.^[14]

These are approximate ranges to aim around, not a schedule to hold yourself to week by week — and the leaner you get, the more it makes sense to sit at the slower end.

The first week or two lie to you

Almost everyone loses faster at the start, and it feels wonderful — but a large share of that early drop is water and glycogen, not fat. Your body stores carbohydrate as glycogen, and muscle biopsy work agrees with the long-held notion that each gram of glycogen is stored with at least 3 grams of water.^[15] Start a deficit or cut carbs, and you shed glycogen and its bound water fast, producing a dramatic first-week number that overstates true fat loss. Re-feed and some of it returns — which is why a single high-carb day can look like a "gain" when no fat was added. Judge your rate on the trend over several weeks once that initial water shift has settled, not on the exciting first reading.

4. Why plateaus happen — and what they aren't

People expect a smooth, straight-line descent. Real fat loss is noisy and stepwise — a staircase with flat stretches. Flat spells of one to two weeks, sometimes longer, are normal and do not mean fat loss has stopped. It helps to separate two very different things that both get called a "plateau."

Water plateaus: the fat is still leaving

Most short "plateaus" are really water masking a real deficit. As you lose fat you can simultaneously retain water for unrelated reasons — refilled glycogen after a bigger carbohydrate day^[15] or the menstrual cycle among them. When 42 women were weighed twice a week through a full cycle, body weight was about 0.45 kg higher during menstruation, an increase accounted for by a 0.47 kg rise in extracellular water with no other significant change in body composition.^[16] Fat leaves while water arrives, so the scale holds flat even though fat is genuinely dropping; when that water later clears, the scale can fall several hundred grams seemingly overnight. The fat was leaving the whole time — only the water was hiding it. This is exactly why weighing under consistent conditions and following a trend, not a single morning, matters so much. It's also why Strathlon's cycle-aware view exists: a temporary cycle-related bump should read as water, not lost progress.

Real plateaus: your maintenance moved

A genuine, multi-week plateau usually has a physiological cause worth understanding rather than fearing. Two things quietly shrink the gap you set:

• A lighter body burns less. As body mass falls, RMR falls too — resting energy expenditure is predicted mainly by how much fat-free mass and fat mass you carry.^[2] The 500 kcal deficit you calculated at your starting weight is a slightly smaller deficit at your new, lighter weight, because your maintenance has dropped underneath you.
• Adaptive thermogenesis. Beyond that expected drop, total daily energy expenditure often falls by more than the loss of body mass predicts; spontaneous, non-exercise movement decreases under an energy deficit, and it can stay suppressed for a while after normal eating resumes.^[10] Its magnitude is individually variable and commonly overstated online. When 171 women were measured under standardised weight-stable conditions, the adaptation averaged about 54 kcal a day after weight loss, was not correlated with weight regain, and was no longer detectable at one- and two-year follow-up.^[17] It slows loss and makes maintenance harder, but it does not halt fat loss or make a true deficit add fat.

Because your maintenance keeps shifting as you get lighter, Strathlon re-centres your targets on a rolling ~7-day trend of your weight rather than a single morning's reading — so as your real weight drifts down, your calorie and protein targets follow it, tracking genuine change while ignoring day-to-day water noise.

The protectable lever inside all of this is muscle. Because RMR tracks fat-free mass,^[2] losing muscle lowers your burn and deepens the plateau, while keeping muscle defends it. Two habits reliably bias your body toward losing fat while sparing muscle: eating enough protein and doing resistance training. For the protein number, a meta-analysis of 49 trials found no further resistance-training gains in fat-free mass beyond a total intake of about 1.6 g/kg a day,^[18] while in a severe deficit more helps: young men in a roughly 40% deficit, training six days a week for four weeks, gained 1.2 kg of lean mass on 2.4 g/kg a day versus 0.1 kg on 1.2 g/kg, and lost 4.8 kg of fat versus 3.5 kg.^[19] Structured resistance training and sufficient protein together are what preserve lean body mass during energy restriction.^[10] Maintaining your lifts in a deficit is one of the best everyday signs that the weight you're losing is fat, not muscle.

5. Diet breaks and maintenance phases

Because a deficit gets harder the longer it runs — adaptation grows, hunger climbs and adherence frays — one of the most useful tools for a longer fat-loss phase is the planned break. A diet break is a deliberate stretch, typically one to two weeks, spent eating at roughly maintenance — not a free-for-all, and not a deeper cut, but a genuine pause at your current calorie balance before resuming the deficit. That one-to-two-week window at maintenance is exactly the strategy proposed in the literature for blunting the adaptations a long diet provokes.^[20]

The evidence is encouraging in one population and neutral in another, and it's worth being even-handed about both. In the MATADOR trial, 47 men with obesity took the same 16 weeks of restriction at 67% of maintenance either continuously or split into 2-week blocks separated by 2-week periods at energy balance. The intermittent group lost more weight (14.1 kg versus 9.1 kg) and more fat (12.3 kg versus 8.0 kg), and their resting energy expenditure fell less — but fat-free mass loss was similar in both groups, and the intermittent schedule took 30 weeks rather than 16 to get there.^[21] In leaner, trained people the picture changes: the ICECAP trial randomised 61 resistance-trained adults to 12 weeks of continuous moderate restriction or the same restriction interrupted by three one-week periods at energy balance, and found no advantage for the breaks in fat loss, fat-free mass, strength, resting energy expenditure, leptin, ghrelin, testosterone or thyroid hormone. What the break group did report was lower hunger, less desire to eat and greater satisfaction.^[22] So: promising but not magic, with the clearest body-composition benefit concentrated in people with more to lose over a longer diet. A break's biggest, most reliable payoff is simply that it makes a long fat-loss phase easier to finish.

A gentler cousin is the maintenance phase: once you've reached a goal, deliberately eating at maintenance for a while lets your body — and your habits — settle at the new weight before you decide whether to lose more. It's also the natural landing point when a structured plan ends, rather than snapping straight back to old eating. If you want the app's take on that transition, see what happens when your plan ends.

6. Why crash diets backfire

A crash diet — a very large deficit, often paired with very low protein and little or no resistance training — is the mirror image of everything above. It looks efficient because the early scale drop is steep, but that speed is bought with costs that tend to make it slower, or worse, over any real timeframe:

• A bigger share of the loss is lean tissue, not fat. As energy intake is reduced further, lean tissue makes up an increasing fraction of the total weight lost.^[9] In the elite-athlete trial above, losing at 1.4% of body weight a week on a 30% intake reduction left lean body mass unchanged, while losing at 0.7% a week on a 19% reduction added 2.1% to it.^[8] You end up lighter but softer.
• Your maintenance drops harder. Resting energy expenditure is driven largely by fat-free mass,^[2] so shedding muscle pushes your burn down on top of the expenditure reductions a deficit already causes^[10] — the very approach that felt fast quietly makes future loss and maintenance harder.
• Training and body composition suffer. In that same trial the fast-loss athletes gained no lean mass and lost a smaller proportion of their fat mass (21% versus 31%) than the slow-loss group.^[8] Under-fuelling undermines the training that would have protected your muscle in the first place.
• Rebound. Restriction ramps up hunger and the hormones behind it, and those changes persist. A year after a very-low-energy diet, leptin was still below and ghrelin still above baseline, and hunger was still elevated, in people who had lost about 13.5 kg — which is why the authors called for long-term strategies to counteract the drive to regain.^[23]
• Weight cycling is less damning than the folklore suggests. Repeated loss and regain is worth avoiding because it's demoralising, but a systematic review of the literature since 1994 found inconclusive evidence that a history of weight cycling affects body composition, and most studies showed no detrimental effect on type 2 diabetes risk; its authors concluded that weight-loss efforts should continue to be encouraged.^[24]
• Genuine clinical risk at the extremes. A chronic large shortfall relative to training load is low energy availability — inadequate energy intake in relation to exercise energy expenditure — and in athletes it can produce Relative Energy Deficiency in Sport (REDs), a syndrome of health and performance consequences recognised by the International Olympic Committee (international) in both female and male athletes.^[25] This is a real reason to be cautious, and a point where professional guidance matters most.

None of this means fast loss is always harmful for everyone — under medical supervision, some people do use faster approaches for specific reasons. But as a default, self-directed strategy, a crash diet trades away muscle, performance, adherence and durability for a fast start that rarely lasts.

7. Worked example: 500 vs 1,000 kcal a day

This is the heart of the guide, because it makes the trade-off concrete. Picture two people at the same starting weight, both wanting to lose fat. One runs a sensible ~500 kcal/day deficit; the other decides to "get it over with" and runs a ~1,000 kcal/day crash deficit. Using the planning estimate of ~7,700 kcal per kilogram^[6] — which, remember, overpredicts real-world loss^[7]:

Read the arithmetic honestly and the crash plan looks tempting: on paper it loses about twice as much per week. Here's the catch the paper hides — doubling the deficit doesn't double the fat loss. The deeper the cut, the larger the lean-tissue share of what comes off.^[9] The elite-athlete trial makes the point starkly: for the same total body-weight loss, the slower group shed 31% of its fat mass and gained 2.1% lean mass, while the faster group shed only 21% of its fat mass and gained none.^[8] Because the moderate dieter is eating enough to train, their muscle — and therefore their RMR^[2] — is largely protected.

Now play it forward. The sensible dieter can hold their plan for months, keeps their strength, and finishes leaner with their metabolism intact — and because the approach is livable, they're far more likely to keep the result. The crash dieter loses fast, then hits stronger hunger that persists long after the diet ends,^[23] a lower burn from lost muscle, and — very often — a rebound that gives much of it back. Over any horizon that matters, the tortoise routinely beats the hare: the smaller deficit tends to deliver more fat lost, better kept.

8. The misconceptions, corrected

Most fat-loss frustration comes from a handful of persistent myths. Here they are, plainly corrected:

• "Eat as little as possible to lose faster." The deeper the cut, the larger the share of the loss that is lean tissue rather than fat.^[9] The best deficit is the smallest one that still produces appreciable weight loss.^[10]
• "Fast loss now, worry about keeping it off later." The way you lose weight shapes what you lose: at 1.4% of body weight a week, elite athletes gained no lean mass and lost proportionally less fat than those going at 0.7%.^[8] Losing at a livable pace, with protein and training, is what makes the result stick.
• "The scale went up overnight, so I gained fat." A kilogram of body-weight change is worth roughly 7,700 kcal^[6] — a surplus no single meal delivers. A same-day rise is water and food weight. Judge the multi-week trend, not yesterday versus today.
• "I've stalled for a few days — my metabolism is damaged." A few days is water noise, and measured adaptation averages tens of kilocalories a day, is uncorrelated with regain, and fades over the following year or two.^[17] A true deficit still mobilises fat.
• "Any break from the diet ruins my progress." A planned week or two at maintenance cost trained dieters nothing in fat loss or fat-free mass and left them less hungry,^[22] and in men with obesity an intermittent schedule produced more fat loss than a continuous one.^[21]
• "Some foods have negative calories, so they burn more than they contain." No food does. The energy cost of processing a nutrient runs from 0–3% for fat up to 20–30% for protein — always a fraction of the food's energy, never more than it.^[4]

9. The bottom line, and how Strathlon helps

• It's one equation. Spend a little more energy than you take in, consistently, over time. Everything else is a detail of how you run that gap.
• Run a moderate deficit. The smallest one that still produces appreciable loss^[10] — often around 300–500 kcal a day — sized to how much you have to lose, not to how impatient you feel.
• Expect a modest, steady rate. Around 0.5–1% of body weight per week^[11][12] — 0.5–1 kg a week in the British Dietetic Association's framing^[13] — once the early water drop settles. Judge it on the multi-week trend.
• Protect muscle. Enough protein — about 1.6 g/kg as a floor,^[18] up to 2.4 g/kg when the deficit is severe^[19] — plus resistance training keeps your loss biased toward fat and defends your metabolism.
• Treat plateaus as information. Short ones are water; long ones mean your maintenance moved. Neither means the equation stopped working.
• Use breaks on purpose. A week or two at maintenance can make a long phase easier to finish, mostly by taking the edge off hunger.^[22]
• Choose patience over the crash. At the same total weight lost, the slower approach lost more fat and gained lean mass; the faster one did neither.^[8]

Where it's honest to say so, Strathlon already turns much of this into numbers you can glance at rather than calculate. It sets your targets around a moderate deficit by default rather than an extreme one, and re-centres them on a rolling ~7-day trend of your weight rather than a single morning's reading, so your calories and protein follow real change and not daily noise; it shows your energy balance and weight trend together, so you learn to read the multi-week signal instead of panicking at a single morning; it gives your protein target a number behind the "protect your muscle" advice; and its cycle-aware view helps a temporary water bump read as what it is. The app is there to make patience easier — to show you the equation is working even on the days the scale pretends it isn't. But the fundamentals on this page hold with or without any app: a moderate gap, protein and training, and time.

References

Every figure in this guide comes from the sources below. Where a number reflects a professional body's consensus rather than a single trial, the citation names that body and the country it belongs to — guidance differs a little between nations, and no one country's advice is the last word. The trials themselves come from Norway, Australia, Canada, Spain, Greece and the United States, and they do not all agree; where they conflict, the guide says so rather than picking the flattering one.

1. Hall KD, Heymsfield SB, Kemnitz JW, Klein S, Schoeller DA, Speakman JR. Energy balance and its components: implications for body weight regulation. American Journal of Clinical Nutrition. 2012;95(4):989–994. Sets out the energy-balance framework for body-weight change and states that resting energy expenditure comprises approximately two-thirds of energy out. PMC3302369
2. Nelson KM, Weinsier RL, Long CL, Schutz Y. Prediction of resting energy expenditure from fat-free mass and fat mass. American Journal of Clinical Nutrition. 1992;56(5):848–856. Across 213 adults, fat-free mass alone accounted for r² = 0.727 of the variance in resting energy expenditure; fat mass explained only a small part of what remained. doi:10.1093/ajcn/56.5.848 · PubMed 1415003
3. Westerterp KR. Control of energy expenditure in humans. In: Endotext. MDText.com; last updated 21 March 2022. States that diet-induced energy expenditure represents about 10% of the energy ingested over 24 hours on a mixed diet at energy balance, that resting energy expenditure is the largest component of daily energy expenditure, and that activity-induced energy expenditure is the most variable component. NCBI Bookshelf NBK278963
4. Westerterp KR. Diet induced thermogenesis. Nutrition & Metabolism. 2004;1:5. Gives 5–15% of daily energy expenditure for a mixed diet eaten at energy balance, and per-nutrient values of 0–3% for fat, 5–10% for carbohydrate, 20–30% for protein and 10–30% for alcohol — the basis for the statement that the cost of processing food is always a fraction of its energy. PMC524030
5. von Loeffelholz C, Birkenfeld AL. Non-exercise activity thermogenesis in human energy homeostasis. In: Endotext. MDText.com; last updated 25 November 2022. States that NEAT is the most variable component of total energy expenditure within and across subjects and can vary by as much as 2,000 kcal per day between two adults of similar body size, lean body mass, age and gender. NCBI Bookshelf NBK279077
6. Wishnofsky M. Caloric equivalents of gained or lost weight. American Journal of Clinical Nutrition. 1958;6(5):542–546. The origin of the 3,500 kcal per pound (~7,700 kcal per kilogram) rule of thumb. doi:10.1093/ajcn/6.5.542 · PubMed 13594881
7. Hall KD, Chow CC. Why is the 3500 kcal per pound weight loss rule wrong? International Journal of Obesity. 2013;37(12):1614. States that the rule was motivated by calculating that a pound of adipose tissue stores approximately 3,500 kcal, that its most serious error is the failure to account for dynamic changes in energy balance, and that it leads to overestimation of weight loss in individuals and populations. PMC3859816
8. Garthe I, Raastad T, Refsnes PE, Koivisto A, Sundgot-Borgen J. 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. 2011;21(2):97–104. Conducted at the Norwegian School of Sport Sciences (Norway). Twenty-four athletes, all doing four resistance sessions a week, lost 0.7% or 1.4% of body weight per week on energy-intake reductions of 19% ± 2% and 30% ± 4%; body weight fell 5.6% and 5.5%, fat mass fell 31% and 21%, and lean body mass rose 2.1% in the slower group while being unchanged (−0.2%) in the faster group. doi:10.1123/ijsnem.21.2.97 · PubMed 21558571
9. Forbes GB. Body fat content influences the body composition response to nutrition and exercise. Annals of the New York Academy of Sciences. 2000;904:359–365. Describes the inverse curvilinear relationship between initial body-fat content and the proportion of weight loss consisting of lean tissue, and states that as energy intake is reduced, lean tissue makes up an increasing fraction of the total weight loss. PubMed 10865771
10. Trexler ET, Smith-Ryan AE, Norton LE. Metabolic adaptation to weight loss: implications for the athlete. Journal of the International Society of Sports Nutrition. 2014;11:7. Source of the recommendation to "utilize the smallest possible deficit that yields appreciable weight loss", of the statement that the decline in total daily energy expenditure often exceeds the magnitude predicted by the loss of body mass, of the observation that non-exercise activity decreases under an energy deficit and may stay suppressed afterwards, and of the statement that structured resistance training and sufficient protein preserve lean body mass during energy restriction. PMC3943438
11. Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition. 2014;11:20. States that caloric intake should be set at a level that results in bodyweight losses of approximately 0.5 to 1%/wk to maximise muscle retention. PMC4033492
12. Aragon AA, Schoenfeld BJ, Wildman R, Kleiner S, VanDusseldorp T, Taylor L, Earnest CP, Arciero PJ, Wilborn C, Kalman DS, Stout JR, Willoughby DS, Campbell B, Arent SM, Bannock L, Smith-Ryan AE, Antonio J. International Society of Sports Nutrition position stand: diets and body composition. Journal of the International Society of Sports Nutrition. 2017;14:16. Issued by the International Society of Sports Nutrition (ISSN), a United States-based professional society with international membership. Repeats the 0.5–1.0% of body weight per week rate and notes that slower weight loss better preserves lean mass as subjects get leaner, citing Garthe's 0.7% versus 1.4% per week. PMC5470183
13. British Dietetic Association (BDA, United Kingdom). How to achieve a healthier weight — Food Fact Sheet. Review date September 2024. States that a weight loss of between 5–10% over three to six months, or one to two pounds (0.5–1 kg) per week, is a realistic target. bda.uk.com/resource/weight-loss.html
14. Roberts BM, Helms ER, Trexler ET, Fitschen PJ. Nutritional recommendations for physique athletes. Journal of Human Kinetics. 2020;71:79–108. States that slower rates of weight loss (≤0.5% of body mass per week) are generally preferable for attenuating unfavourable adaptations to weight loss and losses of fat-free mass. PMC7052702
15. Fernández-Elías VE, Ortega JF, Nelson RK, Mora-Rodriguez R. Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans. European Journal of Applied Physiology. 2015;115(9):1919–1926. Conducted in Spain. Muscle biopsies during recovery gave a storage ratio of 1:3, the authors concluding that the findings agree with the long-held notion that each gram of glycogen is stored in human muscle with at least 3 g of water. doi:10.1007/s00421-015-3175-z · PubMed 25911631
16. Kanellakis S, Skoufas E, Simitsopoulou E, Migdanis A, Migdanis I, Prelorentzou T, Louka A, Moschonis G, Bountouvi E, Androutsos O. Changes in body weight and body composition during the menstrual cycle. American Journal of Human Biology. 2023;35(11):e23951. Conducted in Greece. In 42 women measured twice weekly, body weight was 0.450 kg higher during menstruation, attributable to a 0.474 kg increase in extracellular water, with no other statistically significant change in body composition. doi:10.1002/ajhb.23951 · PubMed 37395124
17. Martins C, Gower BA, Hill JO, Hunter GR. Metabolic adaptation is not a major barrier to weight-loss maintenance. American Journal of Clinical Nutrition. 2020;112(3):558–565. In 171 women measured under weight-stable conditions, metabolic adaptation after weight loss averaged −54 ± 105 kcal/day, was not correlated with weight regain, and was no longer significant at one- and two-year follow-up. PMC7458773
18. Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, Aragon AA, Devries MC, Banfield L, Krieger JW, Phillips SM. 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. 2018;52(6):376–384. Across 49 trials and 1,863 participants, protein supplementation beyond a total intake of 1.62 g/kg/day produced no further gains in fat-free mass (95% CI 1.03 to 2.20). doi:10.1136/bjsports-2017-097608 · PubMed 28698222
19. Longland TM, Oikawa SY, Mitchell CJ, Devries MC, Phillips SM. Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial. American Journal of Clinical Nutrition. 2016;103(3):738–746. Conducted at McMaster University (Canada). Four weeks, a ~40% energy deficit and six training days a week: lean body mass rose 1.2 ± 1.0 kg on 2.4 g/kg/day protein versus 0.1 ± 1.0 kg on 1.2 g/kg/day, and fat mass fell 4.8 ± 1.6 kg versus 3.5 ± 1.4 kg. doi:10.3945/ajcn.115.119339 · PubMed 26817506
20. Ruiz-Castellano C, Espinar S, Contreras C, Mata F, Aragon AA, Martínez-Sanz JM. Achieving an optimal fat loss phase in resistance-trained athletes: a narrative review. Nutrients. 2021;13(9):3255. Conducted in Spain. Describes the strategy of a 1–2 week phase in which caloric intake is raised to maintenance levels to counter the adaptations of a sustained deficit, and attributes the fall in daily energy expenditure partly to lost body mass and partly to reduced non-exercise activity thermogenesis. PMC8471721
21. Byrne NM, Sainsbury A, King NA, Hills AP, Wood RE. Intermittent energy restriction improves weight loss efficiency in obese men: the MATADOR study. International Journal of Obesity. 2018;42(2):129–138. Conducted in Australia. Forty-seven men with obesity took 16 weeks of energy restriction at 67% of maintenance either continuously or as 8 × 2-week blocks alternating with 7 × 2-week blocks at energy balance (30 weeks in total). The intermittent group lost more weight (14.1 ± 5.6 kg versus 9.1 ± 2.9 kg) and more fat mass (12.3 ± 4.8 kg versus 8.0 ± 4.2 kg) and had a smaller fall in resting energy expenditure, while fat-free mass loss was similar between groups. PubMed 28925405 · doi:10.1038/ijo.2017.206
22. Peos JJ, Helms ER, Fournier PA, Ong J, Hall C, Krieger J, Sainsbury A. Continuous versus intermittent dieting for fat loss and fat-free mass retention in resistance-trained adults: the ICECAP trial. Medicine & Science in Sports & Exercise. 2021;53(8):1685–1698. Conducted in Australia. Sixty-one resistance-trained adults did 12 weeks of continuous moderate energy restriction or 4 × 3 weeks of restriction interspersed with 3 × 1 week at energy balance. Similar fat loss and fat-free mass retention were achieved by both, with no differences in strength, resting energy expenditure, leptin, testosterone, IGF-1, free T3 or active ghrelin; the intermittent group reported lower hunger (P = 0.002), lower desire to eat (P = 0.014) and greater satisfaction (P = 0.016). PubMed 33587549 · doi:10.1249/MSS.0000000000002636
23. Sumithran P, Prendergast LA, Delbridge E, Purcell K, Shulkes A, Kriketos A, Proietto J. Long-term persistence of hormonal adaptations to weight loss. New England Journal of Medicine. 2011;365(17):1597–1604. Conducted in Australia. After a mean weight loss of 13.5 ± 0.5 kg, leptin fell and ghrelin rose, and one year later leptin, ghrelin and subjective hunger all still differed significantly from baseline — the authors concluding that long-term strategies may be needed to counteract the drive to regain. doi:10.1056/NEJMoa1105816 · PubMed 22029981
24. Mackie GM, Samocha-Bonet D, Tam CS. Does weight cycling promote obesity and metabolic risk factors? Obesity Research & Clinical Practice. 2017;11(2):131–139. Conducted in Australia. Systematic review of literature published since 1994: evidence that a history or presence of weight cycling influences body composition was inconclusive, 13 of 17 studies (76%) showed no detrimental effect on type 2 diabetes risk, and the authors concluded that weight-loss efforts in people with overweight or obesity should continue to be encouraged. doi:10.1016/j.orcp.2016.10.284 · PubMed 27773644
25. Mountjoy M, Ackerman KE, Bailey DM, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine. 2023;57(17):1073–1097. Issued by the International Olympic Committee (international). Defines REDs as a syndrome of deleterious health and performance outcomes experienced by female and male athletes exposed to low energy availability — inadequate energy intake in relation to exercise energy expenditure. doi:10.1136/bjsports-2023-106994 · PubMed 37752011

This is general educational information, not medical, dietetic or psychological advice. Individual variation is large, and figures such as the ~7,700 kcal ≈ 1 kg estimate, the 0.5–1% per week rate and the 1.6–2.0 g/kg protein guide are approximate, evidence-based estimates rather than exact prescriptions. Anyone with a medical condition (for example a thyroid condition, PCOS, diabetes or heart disease), anyone who is pregnant or breastfeeding, anyone with a history of disordered eating, and any athlete concerned about under-fuelling or REDs should consult a qualified professional before changing how they eat or train. See our Terms for more.

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