"This time it's the right diet"

Every fresh start comes with a story about the last one. The shakes were unrealistic. The fasting didn't suit you. The points were fiddly and the app was annoying. This time it's the sensible one, low sugar, or no bread after lunch, or a plate method, and the sensible one will hold because the problem was the plan.

Look at the envelope again. The rules on it are all different. The endings are all the same. If the rules were the problem, changing them would change the ending, and it hasn't, across a dozen or more tries. What that suggests is that the problem isn't which rules. It's rules. A diet, whatever it forbids, is a set of things you're not allowed, and the research in chapter 3 is about what not-allowed does to people who diet, regardless of what's on the list.

There's a review that looked at where diets end up. Traci Mann and colleagues, in 2007, went through the long-term studies of calorie-restricting diets to see whether dieting works as a treatment for obesity. Their conclusion was that it doesn't. Across the studies, between a third and two-thirds of dieters ended up weighing more than they had before the diet, and the authors argued that the true figure is probably worse, because the studies had methodological problems that all pushed in the direction of making diets look better. People who'd regained dropped out and weren't counted. Weights were self-reported. Follow-ups were short. The review also found no consistent evidence that dieting improved health, whatever happened to weight.

That's a review with a position, written by researchers who set out to answer a policy question, and I'd read it as such. But the direction of the finding is not in dispute among people who study this. Most diets, followed for long enough, end with the weight back and often with more. Not because the dieters chose the wrong one. Because that's what diets do, across all the rules that were tried.

So when the new plan says it's different, ask what it forbids. If it forbids anything, it's a diet, and it's on the envelope already under another name.