A winning diet is one that almost anybody can follow over the long haul. After all, no matter how good a diet is in theory, if you can't stick to it, it can't help you lose weight and keep it off. Or rein in your blood pressure. Or lower your cholesterol, manage diabetes, or provide any of the other benefits a healthy diet can bring.
It's no wonder, then, that serious studies of diet programs like the popular Jenny Craig always look at what experts call "retention" or "adherence"—that is, a plan's success in keeping dieters on board over the weeks, months, and years. High retention rates are enthusiastically promoted by diet programs and merit the attention of consumers. In a recent ranking of seven popular diet programs by Consumer Reports, Jenny Craig wound up at the top. "What gave it the edge," the editors wrote, was a "remarkable level of adherence." That assessment was based on a study in the Journal of the American Medical Association showing that 92 percent of 331 women on the Jenny Craig program had stuck it out for the entire 24-month study period.
That's an impressive figure, but it doesn't necessarily mean what you'd think. The odds of a two-year relationship with Jenny Craig for the average dieter are likely to be a lot lower.
For one thing, the women in the JAMA study (which Jenny Craig funded) paid no enrollment fee and nothing for two years' worth of prepackaged, Jenny Craig-branded meals, plus weekly counseling and other support. Critics, including a New York Times columnist, pounced on Consumer Reports for not mentioning that. The women would have had to shell out $6,600 if they had joined up on their own, a point noted by the researchers in their study. Granted, they would have paid for food regardless, but not nearly as much; a hefty kind of out-of-pocket expense could cause otherwise diligent dieters to lose their way.
Then there's the question of whether 92 percent of the women actually adhered to their Jenny Craig regimen. At the end of the study, in-person clinic visits showed that about 60 percent of the women had shed and kept off at least 5 percent of their initial weight, a common benchmark in diet trials. Sixty percent is considered quite high. Was it because they faithfully followed Jenny Craig? Or partly because of the diet program and partly for other reasons, like added exercise? As for the 40 percent who didn't meet the mark, was Jenny Craig part of the problem? Did they just fall off the wagon? Based on the JAMA study's data, we can't know.
But this was not a study that can be used to compare Jenny to other diets anyway. It was never intended to be a real-world trial. It was designed to find out whether an ideally implemented diet program could promote weight loss, keep the weight off, and help dieters change their behavior. In an E-mail, lead researcher Cheryl Rock, a professor of family and preventive medicine at the University of California, San Diego School of Medicine (and a former member of Jenny Craig's scientific advisory board), explained that such a study is like a drug trial: "The main question is, does it work?" So the study was built around a best-case scenario of motivated dieters, free food, and plenty of feedback, reminders, and other help.
So what would your odds be if you started the Jenny Craig diet today? Consider this: A different study, conducted about 10 years ago and also funded by Jenny Craig, tracked more than 60,000 dieters who enrolled in the program during one 12-month period. It found that half of them dropped out of Jenny Craig within 10 weeks and only 6.6 percent were still in the program after a year.
Anyone in search of a good diet needs good information. Fortunately, rich, reliable info about Jenny Craig and numerous other popular diets is on the way. On June 7, U.S. News will debut its ranking of Best Diets, an editorial project six months in the making. In the fashion of Best Colleges, Best Hospitals, and other U.S. News rankings and ratings, Best Diets will closely examine 20 diets and diet programs from Atkins to Zone. Detailed profiles of each diet will present a complete picture of how the diet works, evidence supporting (or refuting) its claims, and more.
A team of U.S. News editors has been working with a panel of distinguished diet and nutrition experts, who have been scoring the diets according to how they compare on weight loss, heart healthfulness, diabetes prevention and management, and other factors.
Our preliminary findings suggest that while Jenny Craig has a lot going for it, it's not the clear winner. At least half a dozen other diets, in the eyes of our expert panelists, are at least as enticing. One of those diets may turn out to be the Best Diet for you.
Avery Comarow is Health Rankings Editor at U.S. News. He was Washington Editor of Consumer Reports from 1979 to 1982.