This is not medical advice. General information for self-tracking only. If you are under 18, pregnant or breastfeeding, have ever had an eating disorder or a difficult relationship with food, have had gallstones or gallbladder trouble, or are managing a medical condition, talk to a doctor or a registered dietitian before you change your calorie intake. The "fast" arms in the trials below were run by research teams, some of them on 500-calorie diets, and are not something to copy with an app. The full list is here.

Where "1 to 2 pounds a week" comes from

The number most people carry around traces back to the 1998 NIH/NHLBI obesity guidelines. They set an initial goal of losing 10% of body weight over about six months. For people with a BMI in the typical range of 27 to 35, they put the deficit at 300 to 500 calories a day, for a loss of about half a pound to a pound a week. For a BMI over 35, they allow up to 500 to 1,000 calories a day, for about 1 to 2 lb a week.1

Read the guideline itself and it is less of a speed limit than it sounds. It notes that a deficit of 500 to 1,000 calories a day should in theory take off 26 to 52 lb in six months, while what people actually lose over that time is usually 20 to 25 lb. Then it says, in so many words, that "a greater rate of weight loss does not yield a better result at the end of 1 year".1 Nowhere does it say that fast loss comes back faster.

That belief came from somewhere else. Fast or slow weight loss: does the speed you lose it at decide how much of it you keep off? If you are counting calories to lose weight, you have probably been told that slow is safer. When researchers in Melbourne set out to test it, they described it as "a widely held opinion".2

Fast or slow weight loss, randomised

The best test so far is a hospital trial in Melbourne, published in 2014. It enrolled 204 adults aged 18 to 70 with a BMI between 30 and 45, 153 of them women, and randomly assigned them to lose 15% of their body weight either in a 12-week rapid programme or a 36-week gradual one. Anyone who lost at least 12.5% then went on a weight maintenance diet and was followed for 144 weeks, close to three years.2

At the end, both groups had regained most of what they lost, and they had regained the same share of it. Among the people who finished, the gradual group had put back 71.2% of their loss and the rapid group 70.5%. Counting everyone who started, it was 76.3% in both.2 The authors' conclusion is plain: the rate of weight loss did not affect the proportion regained within 144 weeks, and that is "not consistent with present dietary guidelines".2

The figure I find more interesting sits in the first phase. Of the people assigned to the slow programme, 50% reached the 12.5% loss in the time they were given. Of those assigned to the fast one, 81% did.2 Slow did not make the loss stick better, and fewer people got there at all.

None of that makes the fast arm something to try at home. It was a hospital programme with a team running it, and one participant in the rapid group developed an inflamed gallbladder that needed surgery.2 The trial was also unmasked, which a diet trial can hardly avoid, and everyone in it had obesity. What it settles is a narrow question: given the same amount of weight lost, did the faster route lead to more regain? It did not.

A correction to my own site while I am here. The beginner's guide on this blog used to say a 40% calorie cut "gets you a fortnight of misery and a rebound". The misery is fair. The rebound was me repeating the same widely held opinion without checking it, and the trial above does not support it. I have changed that sentence.

A second trial, and the number it did change

A smaller Dutch trial asked the same question with a sharper design. Fifty-seven adults with a BMI of 28 to 35 were randomised to 1,250 calories a day for 12 weeks or 500 calories a day for 5 weeks. They then spent 4 weeks at a stable weight and were followed for 9 months.3

Both groups lost about the same, 8.2 kg on the slower diet and 9.0 kg on the faster one, and regained about the same, 4.2 kg against 4.5 kg.3 So far it agrees with Melbourne.

What differed was what the lost weight was made of. In the 500-calorie group, 8.8% of the weight lost was fat-free mass, which is mostly muscle, organ and water. In the 1,250-calorie group it was 1.3%. Across the whole group, losing a larger share of fat-free mass was associated with more regain at follow-up.3 That is a correlation in 57 people rather than a cause. It does suggest that if losing fast costs you anything, the cost shows up in what you lose rather than in how quickly it returns.

What fast loss is made of

If one small trial were the whole evidence, I would not lean on it. A 2020 meta-analysis pooled the studies that compared gradual and rapid loss in people with overweight or obesity, keeping the total loss the same. Total weight lost really was the same, within 0.03 kg. The gradual route took off about 1 kg more fat, and it lowered body fat percentage a little more. On fat-free mass, though, the pooled studies found no significant difference, which does not match the Dutch trial.4

The same meta-analysis found that gradual loss preserved more of resting metabolic rate, by 407 kJ a day. That is about 97 calories. The abstract prints the confidence interval as 76.76 to 118.01, a range that does not contain its own 407. Read in calories it fits the estimate exactly, so the abstract appears to have mixed its units, and I am reporting it as roughly 77 to 118 calories a day.4 Ninety-seven calories a day is real, and it is also small next to the day-to-day error in any food log.

A second review came at it from another direction. It pulled together 43 studies, 52 groups and 2,379 people who had lost at least 5% of their weight and then regained some. On average they lost 10.9% over 13 weeks and regained 5.4% over the next 44. Both the amount and the rate of loss were associated with regain, and the two interacted. The rate was not associated with how much fat-free mass people lost. The amount was.5 These are comparisons between study groups, not a trial that randomised the pace, so they are weaker than Melbourne. They also do not line up with the Dutch trial on muscle.

Taken together, a slower loss probably keeps a little more fat-burning machinery and takes off a little more fat for the same kilos. Whether it protects muscle, the studies disagree. None of them shows the slow route winning on the thing people actually care about, which is the weight on the scale two or three years later. If muscle is the worry, protein and resistance training have better support than pace,6 and that part is in do you need to track macros.

The people who lose fast early keep more off

There is a second body of evidence, and it points the opposite way from the old advice. In a Florida trial of 262 women with obesity, average age 59, everyone was told to aim for 0.45 kg a week. The researchers then grouped them by what actually happened in the first month. The women who lost fastest, at 0.68 kg a week or more, were 13.5 kg down at six months and 10.9 kg down at eighteen. The slowest, under 0.23 kg a week, were 5.1 kg and 3.7 kg down. Regain between six and eighteen months did not differ significantly between the groups, and the fast group was 5.1 times as likely to be 10% lighter at eighteen months.7

The Look AHEAD trial found the same pattern over eight years in 2,290 adults with type 2 diabetes. People who lost more than 4% in the first month had 2.79 times the odds of being at least 5% lighter at year four, and 1.77 times at year eight, compared with those who lost under 2%.8 Astrup and Rössner had argued the general point back in 2000. A bigger initial loss went with better maintenance in the programmes they reviewed, provided it was followed by a year or two of structured maintenance work.9

I would not read either study as "eat less to lose faster". Neither one assigned anyone a faster pace. They sorted people by how they responded, and the Look AHEAD authors note that differences in adherence between the groups showed up as early as the second month.8 The likeliest story is that the people who lost fast early were the people who were following the plan, and they kept following it. What they do make hard to believe is that a good first month is a warning sign. In both studies it went with better results, years later.

A caution about what "fast" means in your own first month. A lot of the early drop on any diet is glycogen and the water stored with it, which is why early weight is cheap and later weight is expensive. I went through that in why the weight loss plateau usually is not your metabolism. A big first fortnight is partly water. It is still a good sign, just not a rate to expect to keep.

Gallstones: the one risk with a threshold

The argument for not going fast that does have numbers behind it is the gallbladder. A 1995 analysis took nine groups from five prospective studies of people with obesity during active weight loss, and plotted gallstone formation against the rate of loss. The curve was exponential, with risk rising sharply above 1.5 kg a week. The authors concluded that weight loss should not average more than 1.5 kg a week.10 That is a ceiling built from five reports, and it is still the clearest one I found.

A much larger Swedish study filled in the size of it. It matched 3,320 people on a 500-calorie very low calorie diet with 3,320 on a 1,200 to 1,500-calorie diet in the same commercial programme. Over a year, gallstones needing hospital care occurred at 152 per 10,000 person-years on the very low calorie diet against 44 on the low calorie one, a hazard ratio of 3.4. That works out to one extra case for every 92 people on the faster diet.11 Adjusting for how much people had lost by three months brought the ratio down to 2.5, still higher. The authors call the risk "albeit low". It is also an observational study, so the people on each diet may have differed in ways the matching missed.11

So the rate that matters for safety is not "fast versus slow" in the sense the regain argument uses. It is a line somewhere around 1.5 kg a week. The NIH/NHLBI guidelines do not recommend very low calorie diets, under 800 calories a day, for weight loss at all, because the deficit is too large and nutrition falls short without supplements.1 Those belong in a clinic.

What the evidence does not settle

Quite a lot, and the gaps matter more for an ordinary person with a calorie counter app than for anyone in these trials.

Both randomised trials above compared a fast programme run by researchers, in one case a 500-calorie diet, with a slower one. Nobody seems to have randomised people who count calories to lose weight to, say, a 15% deficit against a 30% one, both self-managed, and then followed them for years. The Melbourne result tells you a supervised fast loss is not regained faster. It does not tell you what happens when you cut hard on your own, with no team and no maintenance programme waiting at the end.

The muscle question is open, with one trial against a meta-analysis and a meta-regression. The resting metabolic rate difference, about 97 calories, comes from pooled studies of mixed quality. And everyone in these studies had overweight or obesity. If you are trying to lose the last few kilos from a BMI in the low twenties, none of this was measured on you. The NHLBI deficits are given for a BMI of 27 and up.1

One more, and the most important. In Melbourne between 70% and 76% of the loss came back within about three years, at either speed.2 The rate of loss is not where regain is decided. What happens after the loss is, and that is the subject of maintenance calories and the regain.

What a 15% deficit comes to

The app I build has one pace. On a weight-loss goal MyPlate sets your target at 85% of its maintenance estimate, a 15% deficit, and you cannot type in a bigger one. There is no "aggressive" setting and no goal date.

Take a 38-year-old woman, 168 cm and 82 kg, who trains two or three times a week. Her BMI is 29.1. The app puts her maintenance at 2,354 calories and her weight-loss target at 2,001, a deficit of 353 a day. That sits inside the 300 to 500 the NHLBI guidelines give for her BMI band, which they expect to take off about half a pound to a pound a week.1

A percentage scales with the person. A 50-year-old woman who rarely exercises, 60 kg and 160 cm, gets a deficit of 246. A 30-year-old man of 120 kg and 190 cm who trains four to six times a week gets 580. The first is below the band the guidelines describe, because she is below the BMI they were written for. The second is a little above the 300 to 500 for his BMI of 33.2. Neither comes near the 500-calorie diets in the trials, because no target the app shows ever goes below 1,200 calories for women or 1,500 for men. The NIH/NHLBI guidelines describe low calorie diets of 1,000 to 1,200 calories for women and 1,200 to 1,500 for men,1 and the app takes the top of each range, because nobody is supervising an app.

Two limits I would rather name than have you find. Logging a weigh-in in MyPlate does not recompute the target. The plan is only rewritten when you change your goal or activity level, so as you get lighter the target stays 85% of the maintenance you had at setup, and the real deficit shrinks. And the app does not warn you about pace. It charts the weights you log, and judging the rate is left to you.

How to choose a pace you can count calories at

Since the trials do not crown a winner on regain, the pace is mostly a question of what you can sustain and what is safe. This is the order I would decide it in.

Start with the ceiling. If your weekly average is falling by more than about 1.5 kg a week after the first fortnight, slow down. That is where the gallstone risk climbs,10 and a calorie counter on its own cannot watch for it. Below that line, the guideline bands are a sensible default: 300 to 500 calories a day under maintenance for most people with overweight, more only with a BMI over 35.1

Then pick the deficit you can hold on a bad week, not a good one. The Melbourne finding that 81% of fast losers reached their target against 50% of slow ones came with a hospital team behind it.2 Nobody has measured how a hard cut goes for someone doing it alone.

Then protect the muscle the direct way. A review of muscle loss during dieting found that higher protein intake and exercise, resistance training in particular, both help preserve muscle mass, while noting that protein should be adequate rather than excessive.6 That is better evidence than anything above offers for slowing down.

Finally, judge the rate on four-week averages, not the first fortnight. Plan the maintenance phase before you need it, because in Melbourne most of the loss came back at either speed. And if watching the scale or logging food is making you anxious, stop and talk to a doctor or a registered dietitian. The pace is not worth that.

Common questions

Is slow weight loss better for keeping it off?

Not on the best evidence available. In a randomised trial of 200 adults with obesity, people who lost about 15% of their weight over 12 weeks or over 36 weeks regained the same share, about 71% among those who finished, by almost three years later.2 A smaller trial found the same for regain.3 The fast arms were run by research teams, one of them on 500 calories a day, so this says nothing in favour of crash dieting on your own.

How fast should I lose weight when counting calories?

For most people with overweight, the NIH/NHLBI guidelines suggest a deficit of 300 to 500 calories a day, which they expect to take off about half a pound to a pound a week, with 500 to 1,000 a day reserved for a BMI over 35.1 Whatever you choose, keep the average under about 1.5 kg a week, where the risk of gallstones rises sharply,10 and do not go below 1,200 calories a day as a woman or 1,500 as a man without medical supervision.

Does losing weight fast make you lose muscle?

The studies disagree. One trial found 8.8% of the weight lost on a 500-calorie diet was fat-free mass, against 1.3% on 1,250 calories.3 A meta-analysis of gradual against rapid loss found no significant difference in fat-free mass, though gradual loss took off about 1 kg more fat.4 A review of muscle loss during dieting found adequate protein and exercise, resistance training in particular, help preserve muscle mass.6

Is a big drop in the first week a bad sign?

No. Part of it is water stored with glycogen, so it will not continue at that rate, but faster early loss is linked with better results, not worse. Women who lost 0.68 kg a week or more in their first month were 10.9 kg lighter at 18 months, against 3.7 kg for the slowest group, with no significant difference in regain.7 That reflects who sticks with the plan rather than proof that cutting harder works.

Can a food tracker for weight loss tell me if I am losing too fast?

Only if you look at the trend yourself. A calorie counter app records what you eat and, if you log it, what you weigh. Most will not warn you about the rate. Work out your four-week average change and divide by four. If it is above about 1.5 kg a week after the first fortnight, eat more and consider talking to a doctor.10

Pick the pace you can hold

The idea that slow weight loss stays off and fast weight loss comes back did not survive a randomised test. In the trials, speed changed a little about what was lost, perhaps a kilo of fat and a hundred calories of resting burn. It did not change how much came back. What has numbers behind it is a ceiling of about 1.5 kg a week, a floor of 1,200 or 1,500 calories, and the finding that, in Melbourne, most of the loss came back whichever route people took.

So choose a deficit you can keep through an ordinary month, watch your weekly average rather than the morning number, and spend the effort you were going to spend on the pace on the maintenance phase instead. That is the phase where, in the trials, most of the weight came back.

Sources

Every figure above traces to one of these. If you find a number that doesn't match the source it claims, tell me and I'll correct it.

  1. National Heart, Lung, and Blood Institute, NIH (1998). Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. NIH Publication 98-4083. Read the guidelines →
  2. Purcell K, Sumithran P, Prendergast LA, et al. (2014). The effect of rate of weight loss on long-term weight management: a randomised controlled trial. Lancet Diabetes & Endocrinology, 2(12):954-962. Read on PubMed →
  3. Vink RG, Roumans NJ, Arkenbosch LA, Mariman EC, van Baak MA (2016). The effect of rate of weight loss on long-term weight regain in adults with overweight and obesity. Obesity, 24(2):321-327. Read on PubMed →
  4. Ashtary-Larky D, Bagheri R, Abbasnezhad A, et al. (2020). Effects of gradual weight loss v. rapid weight loss on body composition and RMR: a systematic review and meta-analysis. British Journal of Nutrition, 124(11):1121-1132. Read on PubMed →
  5. Turicchi J, O'Driscoll R, Finlayson G, et al. (2019). Associations between the rate, amount, and composition of weight loss as predictors of spontaneous weight regain in adults achieving clinically significant weight loss: a systematic review and meta-regression. Obesity Reviews, 20(7):935-946. Read on PubMed →
  6. Cava E, Yeat NC, Mittendorfer B (2017). Preserving healthy muscle during weight loss. Advances in Nutrition, 8(3):511-519. Read on PubMed →
  7. Nackers LM, Ross KM, Perri MG (2010). The association between rate of initial weight loss and long-term success in obesity treatment: does slow and steady win the race? International Journal of Behavioral Medicine, 17(3):161-167. Read on PubMed →
  8. Unick JL, Neiberg RH, Hogan PE, et al. (2015). Weight change in the first 2 months of a lifestyle intervention predicts weight changes 8 years later. Obesity, 23(7):1353-1356. Read on PubMed →
  9. Astrup A, Rössner S (2000). Lessons from obesity management programmes: greater initial weight loss improves long-term maintenance. Obesity Reviews, 1(1):17-19. Read on PubMed →
  10. Weinsier RL, Wilson LJ, Lee J (1995). Medically safe rate of weight loss for the treatment of obesity: a guideline based on risk of gallstone formation. American Journal of Medicine, 98(2):115-117. Read on PubMed →
  11. Johansson K, Sundström J, Marcus C, Hemmingsson E, Neovius M (2014). Risk of symptomatic gallstones and cholecystectomy after a very-low-calorie diet or low-calorie diet in a commercial weight loss program: 1-year matched cohort study. International Journal of Obesity, 38(2):279-284. Read on PubMed →

The formulas and limits behind MyPlate's own numbers, with their citations, are on the health sources page.