Friday, 6 July 2012

The National Weight Control Registry: the gold standard in bullcrap (Part 2)

 Last time we looked at the origins of the NWCR and the somewhat underwhelming evidence that weight can be successfully lost and maintained without descending into some seriously disordered ‘health’ behaviours. This time, we’re going to look at what happened to those people after they’d been in the registry for a couple of years.

In a paper published in 2003, six years after the first, the ranks of ‘successful dieters’ had swelled to an astounding 3234. This in a country of 77 million dieters. But we have to work with what we’ve got, so let’s go with that for now. Of the 3200 people who had been in the database for at least two years, only 2400 completed their 2-year assessment. Obviously, we don’t know why the other 800+ registrants did not participate, but at least some of them are likely to have gained weight and been too embarrassed to respond. We do know that they tended to be younger than those who stayed in, weighed more at the time they entered the registry, and had reported greater weight loss. So, not to put too fine a point on it, they were fatter to start with, had lost loads of weight, and then disappeared. Hmmm.

But that still leaves 2400 ‘successful dieters’, you say – so that just proves that it can be done. Well, one year after joining the registry, 1483 of them (66% - or two-thirds) weighed more than they did when they joined. By the end of the second year, that figure had risen to 1630 (72%). In other words, the longer you wait after your starting point, the more people gain weight. This is consistent with what’s been shown in other studies. One of the most comprehensive reviews of long-term dieting success rates reported that in one study, 23% of individuals monitored for less than 2 years had rebounded to more than their baseline weight. The figure for those monitored for over 2 years was 83%. Analysis of studies with longer follow-ups showed that the weight regain doesn't really level off either, even at 5 years.

Getting back to the NWCR, at 2 years from entry into the registry, only 465 people had not regained any weight from their starting point. The researchers point out that this is around 21% - higher than found in typical weight loss trials. But even ignoring the fact that this is 465 of 3234 eligible registrants (or around 14%, not 21%), we’re still talking in the low hundreds – not exactly earth-shattering evidence for dieting success. And we don't yet know what happened over the next few years.

To be fair, the researchers did analyse recovery from weight regain between year one and year two, and this is what they found. Of the 1500-odd people who regained weight between entering the registry and their one-year follow-up, only around 150 of them had lost the weight again by the end of the second year. Unsurprisingly, the more weight they’d regained, the less likely they were to have ‘recovered’. It’s true that the largest proportion of regainers (456 people) was made up of people who had gained less that 3% from their 'successful' weight. Even so, only 80 of them had managed to lose the weight again the following year. Of the 284 people who gained back between 3 and 5% above their entry weight, only 41 of them managed to lose it again by year two. A gain of over 5% of joining weight occurred in about a quarter of the respondents (575 people – this is a rough estimation of the actual numbers – between the graphs and the text, around 120 people magically disappeared). Consider the following an approximation only – don’t try and make the numbers add up – it’s an exercise in futility. So as a rough guide, of the 575 or 627 or whatever people who gained back 5% or more, only 74 of them managed to lose half of it back by year 2, and only 27 people had returned to their starting weight. Twenty-seven. There’s no information what means these rebounders used to get their weight back down to that all-important lower number, especially given that their original maintenance strategies weren’t exactly paragons of healthy behaviour. Probably best not to think about it.

So just to sum up, in a country where over 70 million people are trying to lose weight, a nationwide multimedia campaign has managed to attract around 3000 people who have lost at least 30 pounds from their lifetime maximum weight and kept it off for at least a year, and of these, 72% are regaining weight – with most failing to lose it again.

Having said that, two years is a relatively short time in the grand scheme of things, and the gains weren’t HUGE: the average was only about 8 lbs, although again, there was wide variation. Although other studies have consistently shown weight regain increases with time, these are the SUCCESSFUL weight losers we’re talking about. Maybe they managed to turn it around further down the line? I mean, this paper was published nearly 10 years ago; maybe some longer-term results have been published since then that give greater cause for optimism? Don’t hold your breath, either on the publication of long-term data or the improved maintenance rate. We’re still waiting on that one. But do tune in next time for the final episode of how to make massively disappointing results look like really exciting news.