Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
Scientific American Frontiers Logo
TV Schedule
Alan Alda
For Educators
Previous Shows
Future Shows
Special Features

Losing It

. Web Feature .
Do Diets Work? 3 pages: | 1 | 2 | 3 |

by Julie Moynihan and Maggie Villiger

Photo of healthy foodJanuary 13, 2004 — Roughly 8 out of 10 dieters fail to keep the weight off for any extended period of time. At least, that's what dozens of health and fitness web sites want you to believe. But where does this dismal statistic come from? Are there any legitimate studies to support this claim? After some digging, we were able to come up with two scientific papers that lend support to this figure. But, it wasn't easy.
- - - - - - - - - - - -

There are literally hundreds of papers written about diets, but the trick is figuring out which studies are good and which are bad. For example, some studies are funded by groups or organizations that have a say in how the results are published. While most studies are not this shady, they do suffer from other shortcomings. Many studies are simply too small or don't stick with the subjects long enough to determine whether their diet plan was successful or not.


Diets don't fail — people do...There is a real need for dietary, behavioral, emotional, spiritual, and environmental components to obesity treatment.


Despite these obvious flaws, two papers appear to offer some insight into the question: Do diets work? The first paper, published in 2000, is a systematic review of the best studies ever written on the topic of dieting and obesity. The second paper, published one year later, examines all of the available information and comes up with a norm, or average, for all dieters. Since these studies focus on different aspects of successful weight management, it is difficult to compare their results. They both seem to say, however, that successful dieting is possible -- if only in a small percentage of people.

Sketchy Statistics

According to Danish researchers Ayyad and Andersen, the only way to figure out if diets truly work is to systematically review all of the long-term studies that have been published on the topic. In 2000, they took on the daunting task of reviewing nearly 900 scientific articles that had been published in the last 30 years. Much to their dismay, they found that only 17 of the studies were reliable enough to be included in their comprehensive review. Since Ayyad and Andersen only looked at studies that followed dieters for more than three years, one-third of the studies were thrown out simply because they failed to track the dieters' progress for an adequate period of time.
- - - - - - - - - - - -
3 pages: | 1 | 2 | 3 |

return to show page


Counting DownDebunking the Low-Fat, No-Fat MythLosing Weight the Surgical WayHeavy Hormones?Weighing In Teaching guide Email scientists Watch online Web links & more Contact Search Homepage