"Daily weighing keeps me honest"

Here's where the research really is on your side, up to a point, and it's worth being straight about it. Regular self-weighing has a good record in weight-loss studies. Yaguang Zheng and colleagues reviewed 17 longitudinal studies of adults seeking treatment for their weight and found that regular self-weighing, daily or weekly, was associated with more weight loss and not with depression or anxiety. Rena Wing and colleagues, in a trial of 314 people who had each lost about nineteen kilos, built a maintenance programme around daily weighing and found that after eighteen months about seventy-two per cent of the control group had regained two kilos or more, against forty-six per cent of those who'd had the programme face to face. Daily weighing went up in the programme groups and was associated with less regain. Carly Pacanowski and David Levitsky gave 162 overweight adults a scale and a graph of their weight and found the daily weighers lost a modest amount more over a year, and held it.

So the honest version of the claim is true. Weighing, used as information inside an effort to change something, helps. But look at who these people were and what they were doing. They'd chosen a programme. They were reading the number as a data point on a chart, with lessons and feedback around it, and the studies measured whether the chart went down over months. Claire Madigan and colleagues, in a meta-analysis of randomised trials, found that the one study of self-weighing on its own, with nothing around it, showed no evidence of effect. Adding weighing to a programme helped. And it made no difference whether people were told to weigh daily or weekly.

Now look at what you're doing. You're reading one number, in the second after it settles, as a mark. There's no chart. There's a swing. The honesty in those trials wasn't in the scale, it was in what people did with the reading, which was to plot it and act on the line. That's the part you've dropped, and it's the part that did the work.

I'd put it this way, and it's my interpretation. The scale can't be honest or dishonest. It reports a force. Honesty is in the response, and a response to noise, however sincere, isn't honesty. It's a reflex with a number attached.