Evidence-based dieting

Here at EBL, we’ve written a lot about the health problems associated with obesity in the U.S. The good news is that an estimated 45 million Americans go on diets each year to lose excess weight. But many weight-loss programs are never evaluated in scientific studies, leading participants to spend time, energy and money on programs that are not evidence-based.

This month, researchers at John Hopkins University published a new systematic review that summarizes all of the data available on commercial weight-loss programs. They reviewed thousands of weight-loss studies, but only found 45 that were scientifically rigorous and reliable.  These studies provided data on 11 different commercial weight loss programs.

After evaluating the data, researchers found two programs that were proven to be moderately effective: Weight Watchers and Jenny Craig.  After being on the diets for 12 months, Jenny Craig participants logged nearly 5 percent greater weight loss than the control group, who received counseling. And Weight Watchers participants logged more than 2 percent greater weight loss compared to the control group. Researchers hypothesize that these programs are successful because they involve a high-level of structure and regular in-person contact. (Jenny Craig requires participants to eat prepared meals, while Weight Watchers uses home-cooking.)

Very-low-calorie programs including Health Management Resources, Medifast, and OPTIFAST resulted in at least 4.0 percent greater short-term weight loss than counseling, but these programs were found to be less effective after six months. The Nutrisystem program resulted in nearly 4 percent greater weight loss after 3 months, but longer-term data were not available for this program.

The take-home message here is disappointing. Despite a decades-long obesity epidemic, there is little evidence on how diet and exercise programs help over the long-term. Even though Weight Watchers and Jenny Craig are proven to be effective over the course of a year, it’s important to understand how participants in these programs fare over five or ten years.

For now, the authors of the review recommend trying one of those two programs to lose weight. But their work makes the clear case that researchers need to focus on measuring these programs over time.