April 2019 Issue
Overweight/Obesity: What Does the NWCR Tell Us About Weight Loss?
By Carrie Dennett, MPH, RDN, CD
Vol. 21, No. 4, P. 12
It’s been 25 years since the founding of the National Weight Control Registry (NWCR), billed as the largest prospective investigation of long-term successful weight loss maintenance.1 To date, more than 10,000 adults have enrolled, with about 4,000 active participants at any one time. The registry’s findings are both lauded as a how-to for losing weight permanently and criticized for glorifying what may be disordered eating behaviors.
The NWCR demographics have shifted little since the registry’s early days, says J. Graham Thomas, PhD, an associate research professor in the Weight Control & Diabetes Research Center at Brown University in Providence, Rhode Island. The average participant is in his or her mid to late 40s, and nearly one-half lost weight on their own, while the rest enlisted help from a doctor, nutritionist, or commercial weight loss program.2 Almost all participants report they restricted their food intake and increased physical activity to lose weight.1,2
Although participants have lost an average of 66 lbs and maintained the loss for an average of 5.5 years, to enroll, they need to have lost 30 lbs and maintained that loss for a year.1 While this timeline is consistent with criteria set by the Institute of Medicine,2 some experts believe it’s controversial.
“A year is definitely not enough time to determine ‘success,’ because while it’s not uncommon for people to maintain weight loss for about a year, that’s exactly the time when most people start regaining weight,” says New York–based Christy Harrison, MPH, RD, CDN, host of the Food Psych podcast. “By three to five years, the overwhelming majority of people who’ve intentionally lost weight have regained all of it—and in up to two-thirds of cases, they’ve regained more than they lost.”3
A 2005 critique of the NWCR noted that 72% of the people enrolled in the registry were regaining weight steadily,4 although most participants who stayed actively enrolled still maintained a loss of at least 10% from maximum weight.5
Another criticism of the NWCR is the fact it’s based on self-report. The registry’s annual surveys include a food frequency questionnaire asking participants to estimate average weekly intake of a long list of foods—challenging for occasionally consumed foods, such as seasonal produce. The survey also asks participants their current weight, but not whether they had gained and lost over the previous year. If people stop responding to the questionnaires, their enrollment doesn’t end.
Of the common behavioral traits observed among participants, some do match up with current clinical research, and a few have raised concerns among eating disorder experts.
• Diet composition. Most participants eat a low-calorie, low-fat diet and have reported an average daily intake of 1,381 kcals. However, NWCR researchers estimate that actual calorie intake is likely closer to 1,800 kcals,2 although the low-fat part is still true. A few years after low-carb diets became popular, the researchers conducted an analysis to determine whether the predominant dietary pattern had changed. It hadn’t. “Certainly, the majority are following low fat, although there’s a very vocal minority that has used other methods, including low carb, and have had success,” Thomas says. This is consistent with data from recent randomized controlled trials showing that, on average, low-fat and low-carb diets have equal effects on weight.6
• Meal frequency. Most participants eat four to five times per day, and it’s a commonly accepted idea that eating several small meals per day aids in weight loss or maintenance, theoretically because of better appetite control, stable blood sugar levels, and increased postmeal thermogenesis. However, a 2015 meta-analysis of 15 studies initially found some support for an association between frequency of meals and reductions in body fat and improvements in body composition, but then discovered that the positive findings were the result of one small, short randomized controlled trial, calling the association into question.7
• Early risers. Nearly 8 in 10 participants eat breakfast every day, but while many observational studies show an association between breakfast eating and either weight loss or simply lower BMI, clinical studies haven’t found a causal connection8,9—and a 2016 study found that NWCR participants were more likely to be “morning types” and report better sleep quality and duration than control participants currently enrolled in a weight loss intervention.10 “I think increasingly we’ll find there’s a lot of reciprocal patterns,” Thomas says. “Having an early start to the day is connected to eating breakfast, which could help, and getting to the end of your day and feeling good about your choices could motivate you to continue your healthful choices and help you get to bed earlier.”
• Television and physical activity. Sixty-two percent of participants watch fewer than 10 hours of TV per week11 and 90% exercise about one hour per day on average—far higher than what’s usually recommended in weight loss programs, but consistent with research findings on the levels needed to aid weight loss and maintenance.12 Observational studies on TV viewing and body weight have found it difficult to uncouple TV habits from dietary habits, physical activity habits, and socioeconomic status, all of which can influence weight and health.
• Self-monitoring. A 2017 study found that NWCR participants were more likely than a control group (92.8% vs 71.3%) to track weight, diet, or exercise, and NWCR smartphone owners were 23.1 times more likely to use food, diet, or calorie-counting apps.13 Three-fourths of participants weigh themselves at least once per week. Many studies have found that regular self-weighing may help prevent weight gain or regain and may aid weight loss efforts. However, most trials that use self-weighing as part of the intervention exclude people who have an eating disorder or a history of one, so the potential psychological effects of self-weighing are unclear.14
• Dietary restraint. Participants tend to limit variety in their food choices and take corrective action for small amounts of weight gain. A 2005 NWCR survey found that allowing for flexibility in the diet may create more opportunity for loss of control.2 However, the dietary restraint and vigilance about body weight reported by NWCR participants has drawn comparison to eating disorder behaviors.4 Harrison points to a 2017 study that found what it called “remarkable parallels between the behavioral patterns of successful weight loss maintainers from the NWCR and individuals with chronic anorexia nervosa.” Although the authors of that study state they aren’t suggesting that the sustained weight loss of NWCR participants is pathological, it raises potential concerns.15
The NWCR annual survey does include a measurement of dietary restraint, and registry members have an average score similar to that of patients who recently completed an obesity treatment program—although not as high as eating-disordered patients.2 A 2012 NWCR study stated that “with the exception of high dietary restraint, participants in the NWCR do not show higher levels of psychological symptoms (ie, depression, general emotional distress, binge eating, and self-induced vomiting) than observed in the general population.”16 A 2018 NWCR study found that participants scored higher than a control group on a key measure of self-control—one that’s associated with higher education. It’s unclear whether it’s an inherent trait of successful weight loss maintainers or a learned behavior.17 Thomas says that a study on body image in NWCR participants is currently underway.
‘Weight Loss Secrets’ and Generalizability
About 96% of NWCR participants are white, 80% are women, and 55% have college degrees—of which 29% have graduate degrees1,5—which isn’t a nationally representative sample. A 2005 study coauthored by NWCR founders James O. Hill, PhD, of the University of Colorado in Denver and Rena Wing, PhD, of Brown Medical School, stated, “Because this is not a random sample of those who attempt weight loss, the results have limited generalizability to the entire population of overweight and obese individuals.”18
Despite these demographics, health care providers actively interpret their findings and the media as “proof” that lasting weight loss is possible—if you practice the behaviors of the NWCR participants. However, the NWCR is an observational study, not a clinical trial, and correlations don’t prove causation. If they did, the participant demographics could be used to argue that being white and educated leads to weight loss. And then there are the numbers.
“The NWCR reports that the number of people enrolled is ‘more than 10,000’—which is a tiny fraction of all dieters, less than 0.005%, by my calculations,” Harrison says. “So the NWCR participants are definitely the exception and not the rule when it comes to intentional weight loss.”
Thomas says the registry hasn’t uncovered any secrets. “Most of what we find tends to be quite predictable in a lot of ways. What’s more remarkable is that the individuals are able to do it consistently,” he says. “We’re not finding out that we’re eating this one surprising food. They eat a healthful diet, and they tend not to splurge, and they exercise regularly.”
Many of the common features of NWCR participants—breakfast eating, regular physical activity, limited TV viewing, good sleep habits—have value regardless of someone’s current or desired weight, according to health and nutrition experts. However, when working with patients who have weight concerns, it’s important to assess whether behaviors such as self-weighing and dietary restraint are supporting or detracting from their overall health and well-being.
— Carrie Dennett, MPH, RDN, CD, is the nutrition columnist for The Seattle Times, owner of Nutrition By Carrie, and author of Healthy for Your Life: A Holistic Guide to Optimal Wellness.
1. The National Weight Control Registry website. http://www.nwcr.ws/
2. Wing RR, Phelan S. Long-term weight loss maintenance. Am J Clin Nutr. 2005;82(1 Suppl):222S-225S.
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