Does calorie counting work?

When intake is truly controlled, yes, and that is the foundation every other study on this site rests on. The harder question is whether people can measure their own intake well enough to use it. In a supervised two-year study, a planned 25 percent calorie cut came out at 11.9 percent. When people were asked to report their own intake, under-reporting ran 15 to 47 percent, depending on the method.

Why am I not losing weight when I log everything?

The research has a specific and unflattering answer, and it is not metabolism. Ten people who said they ate under 1,200 calories a day and could not lose weight had their energy burn measured directly. It came out within 5 percent of expected, and their actual food intake was 47 percent higher than they reported. Across five pooled studies, average under-reporting was 28 percent by questionnaire and 15 percent by a single recall, and body mass index predicted how big the error was.

Do the macros matter or just the calories?

For weight, mostly just the calories. POUNDS LOST gave 811 people four lower calorie diets ranging from 20 to 40 percent fat and 15 to 25 percent protein for two years, and found no real difference between any of them. For what the weight is made of, protein matters. When people ate 40 percent less, 2.4 g/kg a day led to a 1.2 kg lean mass gain, against 0.1 kg at 1.2 g/kg a day.

Is tracking bad for your mental health?

It depends on who is doing it, and the evidence cuts both ways. In 105 people diagnosed with an eating disorder, 73 percent of app users felt it fed their disorder. In adults who were not obese, on a supervised two-year calorie cutting study, mood, general health, sleep time and sex life scores all got better rather than worse. Those are different people in different situations, and both findings are real.

Is an app enough on its own?

No, in the one head-to-head test. 212 patients at family doctors' offices were given a free tracking app or not, and the six-month difference in weight was 0.30 kg, which is nothing. Log-ins fell sharply after the first month. Where tracking goes with results, it is inside programs with structure and support, and how often people log tracks with the result more than how long they spend.

Macronutrient-defined11 studies in people cited

Calorie counting and flexible dieting

Written by Aaron CuhaReviewed Sep 2026

Also called: IIFYM, If It Fits Your Macros, Flexible dieting, Tracking, Energy restriction

The one diet where the calorie question flips, because this diet is what every other study uses as its control. The math holds when someone supervises. The measuring does not. A planned 25 percent calorie cut came out at 11.9 percent over two years, and people asked to report what they ate under-reported by 47 percent.

What it actually is

A method rather than a food list. Set a calorie target, weigh and log what you eat, and adjust based on the scale. Flexible dieting and IIFYM (If It Fits Your Macros) add targets for protein, fat and carbs, and on purpose refuse to ban any food within those targets. That is a deliberate contrast with rule-based diets. The difference has its own research behind it, because flexible and rigid self-control around food were measured as different things long before IIFYM had a name.

How its fans say it works

Energy balance. The body's energy stores change with the difference between calories eaten and calories burned. So a steady calorie deficit produces weight loss no matter what the food is. Stated fairly, this is the least exotic claim on this site and also the best supported, because every hospital feeding study used to test every other diet here is itself built on it. The second claim, which flexible dieting actually rests on, is about behaviour. It says that having no banned foods reduces the loss of control that ends diets, so the same deficit lasts longer.

What happened when calories were controlled

Best kind of study available: calories matched

Both groups ate the same number of calories, so a difference comes from what was in the diet, not how much people ate.

Constantly, and that is the point. When intake is truly fixed, the result is predictable, and it is the foundation the rest of this site is built on. For anyone doing this without supervision, the finding that matters is the size of two gaps: between the cut you plan and the cut you achieve, and between what you eat and what you report. Both have been measured.

POUNDS LOST put 811 overweight adults on four lower calorie diets ranging from 20 to 40 percent fat, 15 to 25 percent protein and 35 to 65 percent carbs, with two years of group and one-on-one sessions. At six months every group had lost about 6 kg, or 7 percent of starting weight, and weight started coming back after twelve months. At two years the differences between groups were 3.0 against 3.6 kg by protein, 3.3 against 3.3 kg by fat, and 2.9 against 3.4 kg by carbs, and none was a real difference. Fullness, hunger, satisfaction with the diet and session attendance were similar on all four diets. Attendance was strongly linked to weight loss, at 0.2 kg per session attended.
CALERIE 2 is the best long test of deliberate calorie cutting in people who were not obese. 218 adults aged 21 to 50, with a BMI of 22.0 to 27.9, were assigned two to one to a 25 percent calorie cut or to eating as they liked, for two years, across three clinics. The planned cut was 25 percent. The cut people actually achieved was 11.9 percent, from 2,467 to 2,170 calories a day, against 0.8 percent in the comparison group. That gap, in a supervised study across several clinics with every support available, is the single most useful number on this page.
The same study also answers whether it works. People kept off an average of 7.5 kg, against a 0.1 kg gain in the comparison group, and 71 percent of the loss was fat. LDL, the ratio of total to HDL cholesterol, both blood pressure numbers, CRP (an inflammation marker), insulin sensitivity and a metabolic syndrome score all clearly improved against the comparison group at two years. A check found these gains held even after accounting for the weight change itself.
Freedman 2014 pooled five large studies that checked people's reported intake against objective lab measures. On average, people under-reported their calories by 28 percent on a food questionnaire and 15 percent on a single 24-hour recall. The match between reported and true intake was weak: 0.21 by questionnaire and 0.26 by single recall, rising to 0.31 when three recalls were averaged, where one would be a perfect match. Body mass index was among the strongest predictors of under-reporting. That means the error is biggest in exactly the people most likely to be counting.
Lichtman 1992 measured the reporting problem directly, in ten people who said they could not lose weight while eating under 1,200 calories a day. Their total energy burned and their resting burn came out within 5 percent of the expected values, and the energy used to digest food and to exercise did not differ from other people. That ruled out a slow metabolism. Over 14 days, they under-reported what they ate by 47 percent and over-reported how active they were by 51 percent. It was ten people, and the effect has since been found again at population scale.

What happened when people just ate it

Here the question becomes what happens when people are asked to track, rather than being given their food, and the answer is that the tool alone does very little. Laing 2014 put 212 overweight patients at family doctors' offices on usual care, with or without being set up on a free calorie tracking app. Weight change at six months was tiny and did not differ between groups. The gap was 0.30 kg, with a likely range from 1.50 kg one way to 0.95 kg the other, and there was no difference in blood pressure. The app group did use a personal calorie goal on 2.0 more days a week, a clear result. Most users were very satisfied, and log-ins dropped sharply after the first month. Among people who do keep logging, how often they log tracks with results. Harvey 2019 followed 142 people through a 24-week online program. Time spent tracking fell from 23.2 minutes a day in month one to 14.6 in month six. Among the 65.5 percent still logging at month six, time spent did not differ by weight loss, but the number of daily log-ins did: 2.4 against 1.6 for those who lost at least 5 percent, and 2.7 against 1.7 for those who lost at least 10 percent, both clear results. That is a link seen inside a study, not a head-to-head test, so it cannot tell whether logging causes success or success causes logging. The older review of 22 studies found a steady link between tracking and weight loss, but rated the evidence weak because of flaws in how the studies were run, and noted that in all but two studies the people were mostly white and female. And the study that put four popular diets head to head found weight lost was linked to how well people said they stuck to their diet (a correlation of 0.60, a clear result), and hardly at all to which diet they were on (0.07, not a real link).

Protein, and whether it muddies the result

This is where IIFYM has an argument that plain calorie counting does not, and it is a borrowed one. Setting a protein floor inside a calorie target is the difference between just losing weight and choosing what the weight is made of. The studies that show this are in the protein section and the high protein page, not here. The short version: when people ate 40 percent less, 2.4 g/kg a day led to a 1.2 kg lean mass gain, against 0.1 kg at 1.2 g/kg a day. And over six months of ordinary calorie cutting, 0.8 g/kg a day was enough to lose the weight, but not enough to protect lean mass or the energy burned at rest. No study has tested whether tracking macros yourself, rather than being given the food, delivers that benefit.

The measured intakes behind the protein figures are on the protein page.

What reliably moves

Measure	Direction	From
Body weight	Down, in line with the calorie cut people actually achieve	7.5 kg over two years at an achieved 11.9 percent cut in adults who were not obese. About 6 kg at six months and 4 kg at two years across four lower calorie diets in overweight adults, with no difference between diet mixes.
Planned against achieved calorie cut	A gap of roughly half	25 percent planned, 11.9 percent achieved, over two years, in a supervised study across several clinics. Anyone setting a calorie cut at home should expect the same kind of shortfall.
Reported against actual intake	Under-reported, by a lot	47 percent in ten people measured directly. 28 percent by food questionnaire and 15 percent by a single 24-hour recall, across five pooled studies. Body mass index predicts how big the error is.
Heart and metabolic risk factors	Down across the board	LDL, the ratio of total to HDL cholesterol, both blood pressure numbers, CRP, insulin sensitivity and a metabolic syndrome score all improved at two years, and the gains held after accounting for the weight change.
Mood, quality of life, sleep and sex life	Better or unchanged, which is not what most people expect	In the same two-year study, cutting calories improved depression scores (by 0.76 points on a standard depression questionnaire), reduced tension, raised general health by 6.45 points on a standard health survey, and improved sex drive and relationship scores at 24 months, plus sleep time at 12 months. Effect sizes ran from 0.32 to 0.75. These are self-report questionnaires in adults who were not obese and chose to join a two-year calorie cutting study, which is a selected group.
Sticking with logging	Down over time, steeply	Tracking time fell from 23.2 to 14.6 minutes a day between months one and six, and a third of people had stopped logging entirely. App log-ins fell sharply after the first month in the family doctor study.
Weight regain	Starts around twelve months	In an 811-person two-year study, every group lost about 6 kg by six months and began regaining after twelve, finishing around 3 to 4 kg down. Session attendance predicted the result, at 0.2 kg per session.

Long term, and serious health events

Two years is the limit, and two studies define it. CALERIE 2 shows that a steady, moderate calorie cut in adults who are not obese brings lasting weight loss and broad gains in heart risk factors, at about half the cut that was planned, with quality of life scores that got better rather than worse. POUNDS LOST shows that when 811 people get four different lower calorie diets with two years of professional support, what is in the diet does not matter and showing up does. Neither study counted heart attacks, strokes, broken bones or deaths, and no study of calorie counting done on your own has run beyond two years. The regain curve is the honest headline. Weight loss peaks around six months, regain starts after twelve, and what is left at two years is roughly half of what was lost.

Sources

Study in people2019
2 years of calorie restriction and cardiometabolic risk (CALERIE): exploratory outcomes of a multicentre, phase 2, randomised controlled trial
Lancet Diabetes and Endocrinology
218 healthy adults who were not obese were asked to cut calories by 25 percent or eat as usual for two years. They actually cut 11.9 percent. They lost 7.5 kg, 71 percent of it fat, while the other group stayed about the same. Cholesterol, blood pressure, a sign of inflammation, insulin response and other heart risk markers all improved, even after allowing for the weight loss.
218 healthy non-obese adults randomised 2:1 to 25 percent calorie restriction or ad libitum for two years. Achieved restriction 11.9 percent against a prescribed 25. Weight minus 7.5 kg against plus 0.1, 71 percent fat mass. LDL, total to HDL ratio, blood pressure, C-reactive protein, insulin sensitivity and metabolic syndrome score all improved, robust to adjustment for weight change.
Study in people2016
Effect of Calorie Restriction on Mood, Quality of Life, Sleep, and Sexual Function in Healthy Nonobese Adults: The CALERIE 2 Randomized Clinical Trial
JAMA Internal Medicine
218 healthy adults cut calories for two years. They had better mood scores, less tension and better general health. At 24 months their sex drive and relationships were better, and at 12 months they slept longer. The authors found some good effects on quality of life and no bad ones.
218 adults, two years. Calorie restriction improved depression scores (BDI-II between-group difference minus 0.76), reduced tension, improved general health by 6.45 points and improved sexual drive and relationship at 24 months, and sleep duration at 12 months. Effect sizes 0.32 to 0.75. Conclusion: some positive effects and no negative effects on health-related quality of life.
Study in people1992
Discrepancy between self-reported and actual caloric intake and exercise in obese subjects
New England Journal of Medicine
Ten people with obesity said they could not lose weight on under 1,200 calories a day. Tests showed their metabolism was normal, within 5 percent of what was expected. In fact they under-reported their food by 47 percent and over-reported their exercise by 51 percent.
Ten people reporting diet resistance at under 1,200 kcal/day. Total energy expenditure and resting metabolic rate within 5 percent of predicted, thermic effects normal. Food intake under-reported by 47 plus or minus 16 percent and physical activity over-reported by 51 plus or minus 75 percent.
Review of studies2014
Pooled results from 5 validation studies of dietary self-report instruments using recovery biomarkers for energy and protein intake
American Journal of Epidemiology
Five large studies checked what people said they ate against lab tests of what they really took in. Food questionnaires missed calories by 28 percent on average, and a single one day food recall missed by 15 percent. What people reported matched the truth poorly. People with a higher body mass index under-reported more.
Five large validation studies against recovery biomarkers. Average under-reporting of energy 28 percent by food frequency questionnaire and 15 percent by a single 24-hour recall. Correlations of reported with true energy 0.21 and 0.26, rising to 0.31 across three recalls. Body mass index strongly predicted under-reporting.
Study in people2009
Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates
New England Journal of Medicine
811 overweight adults tried one of four lower calorie diets with different mixes of protein, fat and carbs, for two years, with group and one on one sessions. They lost about 6 kg by six months and started to regain after twelve. The mix of protein, fat and carbs made no real difference at two years. People who came to more sessions lost more, about 0.2 kg per session.
POUNDS LOST. 811 overweight adults, four reduced-calorie diets, two years of group and individual sessions. About 6 kg lost at six months with regain after twelve. Two-year differences by protein, fat and carbohydrate all p above 0.20. Session attendance strongly associated with loss at 0.2 kg per session.
Study in people2014
Effectiveness of a smartphone application for weight loss compared with usual care in overweight primary care patients: a randomized, controlled trial
Annals of Internal Medicine
212 patients of family doctors got usual care, with or without a free calorie tracking phone app. After six months, weight was no different between the groups, and neither was blood pressure. App users worked to a calorie goal on 2.0 more days a week, but logins fell sharply after the first month.
212 primary care patients randomised to usual care with or without a free calorie tracking app. Between-group weight difference at six months minus 0.30 kg (95% CI minus 1.50 to 0.95, p = 0.63) and no difference in systolic pressure. App use produced 2.0 more days a week of using a calorie goal, and log-ins fell sharply after month one.
Study in people2019
Log Often, Lose More: Electronic Dietary Self-Monitoring for Weight Loss
Obesity
142 people did a 24 week online weight loss program. Time spent logging food fell from 23.2 minutes a day in month one to 14.6 in month six, and 65.5 percent were still logging. People who logged in more often were more likely to lose 5 or 10 percent of their weight. This is a link inside one study, not proof that logging caused the loss.
142 participants in a 24-week online programme. Self-monitoring time fell from 23.2 minutes a day in month one to 14.6 in month six, with 65.5 percent still logging. Among those, log-ins per day were 2.4 against 1.6 for at least 5 percent loss and 2.7 against 1.7 for at least 10 percent, both p < 0.001. Association within a trial, not a randomised comparison.
Review of studies2011
Self-monitoring in weight loss: a systematic review of the literature
Journal of the American Dietetic Association
A review of 22 studies on tracking food, exercise or weight. Tracking went with more weight loss again and again. But the authors rated the evidence weak because the studies had flaws. In all but two studies, most people were white women.
22 studies of dietary, exercise and weight self-monitoring. A significant association with weight loss was consistently found and the level of evidence was rated weak because of methodological limitations. In all but two studies the samples were predominantly white and female.
Study in people2005
Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial
JAMA
160 adults tried Atkins, Ornish, Weight Watchers or Zone for one year. They lost 2.1 to 3.3 kg, and only 50 to 65 percent finished. How much people lost tracked how well they said they stuck to the diet, not which diet they were on.
160 adults, four popular diets, one year. Weight loss 2.1 to 3.3 kg with completion rates of 50 to 65 percent. Amount of weight lost was associated with self-reported adherence (r = 0.60, p < 0.001) and not with diet type (r = 0.07, p = 0.40).
Study in people1999
Flexible vs. Rigid dieting strategies: relationship with adverse behavioral outcomes
Appetite
A one time survey of 223 adults. Flexible dieting went with less overeating, lower body weight, and less depression and anxiety. Counting calories and strict dieting went with overeating alone and higher body weight. It shows links, not cause and effect.
223 community adults. The strongest canonical correlation (r = 0.65) linked flexible dieting with absence of overeating, lower body mass and lower depression and anxiety. The second (r = 0.59) linked calorie counting and conscious dieting with overeating while alone and higher body mass. Cross-sectional.
Study in people1999
Validation of the flexible and rigid control dimensions of dietary restraint
International Journal of Eating Disorders
Three studies, including 54,517 people in a weight program and 1,838 people from the general public. Rigid control of eating went with more loss of control, higher BMI and more frequent and severe binges. Flexible control went with the opposite, and with a better chance of losing weight over a year.
Three studies including 54,517 weight programme participants and a 1,838-person population sample. Rigid control was associated with higher disinhibition, higher BMI and more frequent and severe binge episodes; flexible control with the opposite and with a higher probability of successful weight reduction over a year.
Study in people2017
My Fitness Pal calorie tracker usage in the eating disorders
Eating Behaviors
105 people with an eating disorder were surveyed. About 75 percent used the MyFitnessPal app, and 73 percent of those felt it fed their eating disorder. The worse their symptoms, the more they felt that way. It is a one time survey of how people saw it.
105 people diagnosed with an eating disorder. About 75 percent used the app, and 73 percent of those users perceived it as contributing to their eating disorder, with that perception correlated with symptom severity. Cross-sectional and self-perceived.
Study in people2012
Effect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial
JAMA
Cited here for the calorie side. In a hospital ward, people overfed by 954 calories a day gained about the same body fat on 5, 15 or 25 percent protein. The authors concluded that the calories alone explain the fat gain.
Cited here for the energy side. In an inpatient metabolic unit, a 954 kcal/day surplus produced similar body fat gain at 5, 15 and 25 percent protein, and the authors concluded that calories alone account for the increase in fat.

What people report

These are things people say about their own eating. Nobody checked them, so they are not evidence. They are here because they tell you what to expect and what to watch for, which the studies do not. They cannot tell you whether anything works.

A sharp early shock at how much higher the logged total is than the guess. This is reported almost universally in the first week, and it fits the measured under-reporting.
Freedom rather than restriction is the most common positive report from flexible dieting in particular, because no food is off the list.
No effect at all, reported often by people who logged for weeks without losing weight. The data on reporting accuracy would put that down to logging errors, not metabolism.
Obsessive checking, anxiety about eating food that has not been weighed, and turning down social meals. This is reported often enough that the flexible dieting community itself treats it as the main way this approach goes wrong.
Giving up within four to eight weeks, the single most common result reported. It matches the study data showing log-ins falling sharply after month one.
Relying on database entries that are wrong, especially ones added by other users, described as a constant and unfixable source of error.
Relief at stopping, reported by long-term trackers who switched to habit-based eating and kept the weight off. No study has tested this.

Sources: r/loseit, r/1200isplenty and r/flexibledieting, coaching write-ups, and the data on sticking with it inside the studies, which is the more useful half: tracking time falling from 23.2 to 14.6 minutes a day over six months, and a third of people logging nothing at all by month six. Otherwise unchecked self-report.

Who this is wrong for

Anyone with an eating disorder now or in the past. Among 105 people diagnosed with an eating disorder, about 75 percent used a calorie tracking app, and 73 percent of those users felt it fed their disorder. The worse their symptoms, the more they felt this. That is a one-time survey of people's own views, and it is the most direct evidence there is on this question.
Anyone whose self-control around food is rigid rather than flexible. In a study across 54,517 weight program members and a separate group of 1,838 people from the general population, rigid control went with more loss of control around food, higher BMI, and more frequent and more severe binges. Flexible control went with the opposite, and with a better chance of losing weight over a year. This shows a link, not cause and effect. It fits a separate community study where calorie counting and deliberate dieting grouped together with overeating alone.
Anyone who will treat a logged number as a measurement rather than an estimate. The gap between reported and actual intake is 15 to 47 percent, depending on the method, and it is biggest in people with a higher BMI.
Children and teenagers. No study of this practice exists in them, and the eating disorder signal is the relevant risk.
Anyone who is pregnant or breastfeeding. Cutting calories on purpose is a medical decision there, not a do-it-yourself one.
Anyone using it as the whole plan. At family doctors' offices, handing people a tracking app and nothing else made a weight difference of 0.30 kg at six months, which is nothing.

Questions

Does calorie counting work?: When intake is truly controlled, yes, and that is the foundation every other study on this site rests on. The harder question is whether people can measure their own intake well enough to use it. In a supervised two-year study, a planned 25 percent calorie cut came out at 11.9 percent. When people were asked to report their own intake, under-reporting ran 15 to 47 percent, depending on the method.
Why am I not losing weight when I log everything?: The research has a specific and unflattering answer, and it is not metabolism. Ten people who said they ate under 1,200 calories a day and could not lose weight had their energy burn measured directly. It came out within 5 percent of expected, and their actual food intake was 47 percent higher than they reported. Across five pooled studies, average under-reporting was 28 percent by questionnaire and 15 percent by a single recall, and body mass index predicted how big the error was.
Do the macros matter or just the calories?: For weight, mostly just the calories. POUNDS LOST gave 811 people four lower calorie diets ranging from 20 to 40 percent fat and 15 to 25 percent protein for two years, and found no real difference between any of them. For what the weight is made of, protein matters. When people ate 40 percent less, 2.4 g/kg a day led to a 1.2 kg lean mass gain, against 0.1 kg at 1.2 g/kg a day.
Is tracking bad for your mental health?: It depends on who is doing it, and the evidence cuts both ways. In 105 people diagnosed with an eating disorder, 73 percent of app users felt it fed their disorder. In adults who were not obese, on a supervised two-year calorie cutting study, mood, general health, sleep time and sex life scores all got better rather than worse. Those are different people in different situations, and both findings are real.
Is an app enough on its own?: No, in the one head-to-head test. 212 patients at family doctors' offices were given a free tracking app or not, and the six-month difference in weight was 0.30 kg, which is nothing. Log-ins fell sharply after the first month. Where tracking goes with results, it is inside programs with structure and support, and how often people log tracks with the result more than how long they spend.