Ok, I pulled the paper from the original literature and took a look. All weights and height for BMI calculation are self-reported, and the paper does acknowledge that this is a potential weakness of the study, with reference to studies that show women under-report weight, and men over-report height. Participants were asked their height, their maximum weight, their weight one year ago, and their weight today.
The 10% weight loss is based on highest weight and the 5% weight regain is based on weight one year ago. Once again, this is quite clear in the original paper, but not necessarily in the WebMD article that quotes it (referenced above). People who lost 10% of their maximum weight were included in the study, and the cutoff between weight regain and weight maintenance was defined as a gain of 5% of last year's weight.
The sample is relatively large (1310), and at least makes an attempt to be representative of the population of the US at large (or at least the "civilian, non-institutionalized" population), as opposed to self-reported weight maintenance success stories (like our beloved National Weight Control Registry) or graduates of one particular weight loss program or another.
Factors associated with weight regain the authors found include:
- Mexican American ethnicity
- greater percentage of maximum weight lost
- fewer years since reaching maximum weight
- attempting to control weight
- greater daily screen time (non-work computer + TV)
- not meeting physical activity recommendations
The authors also make no claims of causality with these associations, and in fact point out that it is possible that the attempt at weight control is a result
of the regain, and not the cause, as there was absolutely no attempt to figure out which came first. They also note that their data was not sufficient to analyze the nutritional side of weight regain.
One point I found interesting is that there was no difference in regain patterns in those who met the "improved health" exercise guidelines of 30 min a day of moderate activity, 5 times a week, and those who met the "sustaining weight loss" guidelines of moderate activity 5 or more times a week, greater than 60 minutes a day.
Other factors considered where no statistically significant effects on weight regain were found:
- Education level
- BMI one year ago
- Smoking status
- Average weekly restaurant food consumption
The paper has a lot of discussion of relative risks of regain for each of these associations and the statistical confidence intervals, that I won't go into here. Note that this paper is about as far as it gets from my own area of expertise, but I didn't find any egregious errors or extravagant claims and was generally impressed with the quality of the study. I think it points out a number of areas to look in more deeply.
Again, what I consider to be the biggest eye opener of the study, almost 2/3 of the people who have lost 10% of their maximum weight, are maintaining most of that weight loss a year later. This is fantastic news! Note that this isn't people maintaining a goal weight, or never gaining an ounce for the rest of their lives, but from a health perspective these numbers are very significant. I am encouraged.