How often should you weigh yourself? What the studies measure

There is no proven ideal frequency. If you want to lose weight, weighing once a week within a plan appears to work about as well as daily: trials that asked for daily weighing did no significantly better than trials that asked for less frequent weighing. The two rhythms have not yet been tested head to head.

If you want to keep weight off after losing it, the evidence comes mainly from (near-)daily weighing. The studies also suggest that what you do with the number and who keeps an eye on it matter at least as much as the number of weigh-ins. And if this morning's number decides what you eat today, you are better off weighing less often.

The man in the image is the physician Santorio Santorio. He weighed himself, his food and his excretions and published a book about it in 1614. Below you will find what has been measured four centuries later, how much your weight fluctuates in an ordinary week and who paid for the research.

Daily or weekly: what the randomised trials say

The best summary comes from a meta-analysis that admitted only randomised trials. Fifteen trials compared a weight loss programme in which participants weighed themselves with minimal or no support. The difference was 3.4 kilos more weight loss, with a confidence interval of 2.6 to 4.2 kilos.

The researchers split those trials up. Seven asked for daily weighing, eight for less frequent weighing, such as weekly. In the trials that asked for less than daily weighing, the difference from the control group was 3.3 kilos. Between the two groups they found no significant difference. Two caveats. This is a comparison between studies. Whether participants actually weighed that often was not measured in those trials.

Weighing without further support is a different story. In the only trial the meta-analysis found on the question, 183 adults with obesity received a scale, a record card to work out their weekly average and a target. After three months they had lost 0.5 kilos more than the control group. That difference was not statistically significant. The confidence interval was too wide to rule out a worthwhile effect.

The programmes with clear results added lessons, feedback and someone keeping an eye on the numbers to the weighing.

Source: Madigan et al.¹ 2015, International Journal of Behavioral Nutrition and Physical Activity · Madigan et al. 2014, International Journal of Behavioral Nutrition and Physical Activity

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Why the strongest results still come with daily weighing

Read the large American trials and daily weighing keeps turning up. In a study of 91 adults with overweight, participants received a scale that transmitted every measurement, a graph of their progress and tailored feedback every week. After six months they had lost an average of 6.55 per cent of their weight. In the control group it was 0.35 per cent.

In 314 people who had already lost an average of 19.3 kilos, a programme revolved around daily weighing and adjusting. After eighteen months, 72.4 per cent of the control group had regained at least 2.3 kilos. Among those who followed the programme face to face, it was 45.7 per cent.

In 599 young adults, two programmes revolved around frequent weighing to prevent weight gain. Averaged over all measurements across three years, the control group sat 0.26 kilos above its starting weight. The most intensive programme group sat 2.37 kilos below it. At two years it was +0.54 versus -1.50 kilos.

In each of those studies, weighing was one part of a package with lessons, feedback and support. They show that daily weighing works well within a system. How much of the effect comes from the weighing itself, they cannot tell you.

Source: Steinberg et al.³ 2013, Obesity · Wing et al.⁵ 2006, New England Journal of Medicine · Wing et al. 2016, JAMA Internal Medicine

Why one measurement tells you little

Your weight follows a weekly rhythm. In 368 Australian adults who weighed themselves for a year, weight fluctuated by about 0.3 per cent every week, an average of 252 grams. Monday and Tuesday were the heaviest days, Friday the lightest.

A European study with 1421 participants found the same pattern: 0.35 per cent fluctuation within the week, up at the weekend and down again on weekdays. Around Christmas weight rose by an average of 1.35 per cent, measured from the lowest point in the month before to the highest in the month after. That rise had not fully disappeared in the months that followed.

These are average patterns of a whole group. They show what the weekly rhythm looks like. How much your own scale jumps from day to day is not what they measure.

If you weigh yourself on Monday and compare it with Friday, you see a rise that belongs to the weekly rhythm. So always compare the same day with the same day. Better still: set one weekly average against the previous one.

Source: Maher et al.¹¹ 2023, JAMA Network Open · Turicchi et al.¹⁰ 2020, PLoS ONE

Regular and near-daily

One study followed 74 adults for nine months after an online weight loss programme, with a scale that recorded every measurement. What went with less regain was the number of weeks in which they weighed on at least six days. Consistency on fewer days a week and the total number of weighing days were not related to it.

This is an observational study. So it may work the other way round: people who are doing well step onto the scale more readily. For the period after weight loss, it still points the same way as the large trials: almost every day and without long gaps.

In the study with 91 participants, the smart scale recorded an average of 4.0 weighing days a week in the three months after the programme, against 6.1 during it. The authors note part of this may be a measurement issue.

The lesson I take from it: choose a rhythm you can keep up in a busy week too. An average only means something if the measurements behind it are regular.

Source: Brockmann et al.⁷ 2020, Obesity · Steinberg et al.³ 2013, Obesity

Someone who keeps an eye on it

The same meta-analysis holds the number I find most interesting. In fourteen trials, participants knew that a coach or researcher could see their measurements. There the difference with the control group reached 3.6 kilos. In the two trials without that oversight it was 2.3 kilos (p = 0.03).

In two trials participants even knew that the coach would contact them if they did not weigh themselves. There the differences rose to 5.6 and 8.8 kilos.

One caveat: this is a comparison between studies that also differ on other points. The authors themselves call this analysis observational.

It does match what I hear in my coaching. A client told me, before the plan was even properly running: 'Just knowing you're watching, I'm already doing more.'

Source: Madigan et al.¹ 2015, International Journal of Behavioral Nutrition and Physical Activity

Does weighing yourself every day make you unhappy?

In adults trying to lose weight, the research does not point that way. In the trial with 91 participants, 47 of whom were told to weigh daily, the researchers saw no increase in depressive symptoms or binge eating. People with a history of eating disorders were excluded. Dissatisfaction with their own body fell. Deliberate restriction of what they ate increased.

A meta-analysis of 29 tests with 10,775 participants found no link between self-weighing and mood, body image or disordered eating. Only psychological functioning, such as self-esteem, showed a small negative association (r = -0.08). The authors saw more negative outcomes in younger participants, in people of normal weight, in those who lost little and in those who weighed themselves outside a supported programme.

Teenagers are a different matter. In an American study of 2516 young people, frequent weighing in girls predicted more binge eating and unhealthy weight control five years later. In boys the researchers did not see that link.

And then there is the sentence I regularly hear in conversations: 'When I see it go up, I really eat less that day.' At that point the scale decides what goes on your plate. If you recognise yourself in that or have an eating disorder behind you, weigh yourself less often or hand the weighing over to someone else for a while.

Source: Steinberg et al.³ 2014, American Journal of Preventive Medicine · Benn et al.⁸ 2016, Health Psychology Review · Neumark-Sztainer et al.⁹ 2006, Journal of Adolescent Health

Who paid for the research

As a historian I always look at who settled the bill. Little stands out here, apart from one declaration of interest.

The American trials I cite were funded by the National Institutes of Health, one of them topped up with a university award. The two British studies on self-weighing received British public money, the meta-analysis on the psychological effects money from the European Research Council. No scale manufacturer is listed as a funder.

The declaration of interest: one of the authors of the three-year study in young adults sat on the scientific advisory board of a large commercial weight loss company. The same author also co-wrote three other studies above, published before joining that board.

And then a detail that made me smile. The meta-analysis notes that widely used British weight loss programmes at the time advised their participants against weighing themselves at home. According to the same authors, participants in such group programmes often name the weekly weigh-in in front of the group leader as the part that keeps them most on track.

Source: Wing et al.⁵ 2016, JAMA Internal Medicine · Benn et al.⁸ 2016, Health Psychology Review · Madigan et al.¹ 2015, International Journal of Behavioral Nutrition and Physical Activity

How to approach it in practice

If you weigh yourself daily, always do it at the same moment: in the morning, after using the toilet, before eating or drinking and on the same scale. Look at the seven-day average and compare it with the week before.

If you weigh yourself once a week, choose a fixed day and stick to it. Because of the weekly rhythm, setting a Monday against a Friday is an unfair comparison. If the number decides your mood or your plate, move to once a week or less.

If you train with weights, the scale tells only part of the story. Muscle grows slowly and your waist measurement or your strength numbers often say more about your progress.

In my coaching I work with two to three fasted measurements a week and I go by the trend over weeks. That is a practical choice. For keeping weight off after losing it, the research leans towards near-daily weighing. What the studies show: weighing works within a plan. With someone who watches the line with you, it possibly works even better.

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