While no commercial weight loss plan can deliver the exaggerated results a few promise, some — in particular Weight Watchers and Jenny Craig — have proven at least somewhat effective in helping people take weight off and keep it off, a research review has found.

Doctors at Johns Hopkins University surveyed existing scientific literature to find studies involving 11 commercial weight loss programs, looking to see which of those studies had good data supporting their findings.

Surprisingly, they found that most of the studies did not actually track how much weight people lost on the various weight loss regimens such as Jenny Craig, Weight Watchers, Slim-Fast, Nutrisystem and others.

Of the 4,212 studies, only 45 were conducted under the under the "gold standard" scientific method of randomly assigning people to a weight loss program or not, and then tracking their weight changes over time, the researchers say in the Annals of Internal Medicine.

"The majority [of programs] still have no rigorous trials done," says Johns Hopkins assistant professor of medicine Kimberly Gudzune.

Trials that were performed had significant shortcomings, including insufficient duration or follow-up, high dropout rate of participants and poor adherence to the diet programs being studied, the researchers say.

Of the programs featured in the studies, only Weight Watchers and Jenny Craig managed to show even modest weight losses after one year, they found, with people on Weight Watchers losing 3 percent of their starting weight and Jenny Craig users losing almost 5 percent.

Still, Gudzune acknowledges, such 3 percent to 5 percent weight loss is considered under most weight management guidelines to be an important first step toward a long-term healthy weight figure.

"Even that small amount of weight loss can help to lower blood sugar, improve cholesterol profiles, help to lower blood pressure and ultimately prevent things like diabetes," she says.

Programs at Weight Watchers and Jenny Craig include some form of coaching, behavioral counseling or social support, all considered vital for long-term success in losing weight, an editorial accompanying the published study said.

Addressing that, editorial author Christina Wee wrote that the study "highlights something that researchers in the behavioral weight management field have known for decades: Structure and intensity of contact are highly correlated with program success."

However, she noted, the weight loss potential of even the most successful commercial programs "is modest and likely below patients' expectations."