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Stanford Report, May 28, 2003

Scientific study investigates ‘fad’ diets; volunteers needed


While millions of overweight Americans have turned to popular diets such as the Atkins, Zone and Ornish regimens, questions about long-term health and the diets’ effectiveness remain unanswered.

There have been conflicting reports as to which diets work best and why, particularly on the issue of carbohydrate intake. And while critics of low-carbohydrate, high-protein plans warn that they could lead to long-term kidney damage and heart disease, proponents say no evidence supports such claims.

Scant research has addressed these questions in a scientifically rigorous way – until now.

The Stanford Center for Research in Disease Prevention is conducting a first-of-its-kind study comparing four popular diet plans head-to-head over 12 months. The study, which is seeking participants among moderately overweight pre-menopausal women in the Bay Area, will track the average weight loss for each of four groups assigned to one of the diets and will evaluate the impact on cholesterol, body fat and other health measures.

Most prior studies have lasted only three to six months, and none have compared several diets across the full spectrum of carbohydrate intake. Unlike other diet studies, which focus solely on weight loss, the Stanford study also will consider a crucial, practical issue: how easy or difficult it was for participants to stick to their diet and why.

"So many people have been asking questions about these diets for years. We think it’s time to give them some answers," said Christopher Gardner, PhD, assistant professor of medicine, who is leading the study. Gardner said the study’s objectives are timely and relevant given that "we have an epidemic of obesity that’s still on the rise, and the ideas of our best and brightest people haven’t been able to change that."

Participants will be randomly assigned to one of four diets for a year: the Atkins diet, which emphasizes unrestricted fat and protein and very low carbohydrate intake; the Zone diet, which prescribes a 40/30/30 balance of carbohydrate, fat and protein, respectively; the Ornish diet, a vegetarian regimen emphasizing high carbohydrate and very low fat intake; and a traditional weight-loss program that emphasizes exercise and social support along with consuming fewer calories and adhering to the U.S. Department of Agriculture’s Food Guide Pyramid.

All participants will take eight weeks of free classes covering their assigned diet plan. The classes, which are taught by a nutritionist and include reading and homework, will help participants understand and follow their diet. After the eight weeks, participants will receive periodic phone calls from the study staff to find out how they’re doing.

Significantly, after the eight weeks of classes, the study staff won’t provide any more assistance to participants who may be having trouble following the diets. Instead, the staff will closely document the proportion of participants still following their diets and, for those who aren’t, what their challenges may have been.

Participants will also make four clinic visits during which their weight, blood pressure and body fat percentage will be measured, and blood samples will be taken to monitor levels of cholesterol, glucose and insulin. Finally, participants will complete questionnaires asking about their experiences and perceptions of their diet.

While a perfect diet study would feature only participants who always follow their diet religiously, Gardner said his research team understands that participants will sometimes stray while others will abandon their diet plan altogether. Knowing this, Gardner said the researchers will seek as much information as possible about the reasons for the participants’ difficulties.
"We’re very interested in that information because it could be enormously helpful for people trying to decide which diet to go on," he said.

Gardner’s research staff has already seen some interesting results from the first group of participants, who have now finished the first phase of the study. He said the most "amazing" result is that after the eight weeks of classes, all but five of the original 74 participants were still participating and trying to follow their diets with few complaints.
Many participants reported weight loss, greater physical and emotional energy, increased physical activity and positive lifestyle changes. Also significant, Gardner said, is the number of people who were happy with their assigned diet even though they initially expressed objections to it. "Several people have said, ‘I would never have picked this diet for myself, but I can see it’s working for me and I like it.’ "

Pre-menopausal women ages 25 to 50 who are 15 to 75 pounds overweight but generally healthy are eligible. Participants must attend one evening class per week for eight weeks on the Stanford campus and make four clinic visits over the year. Call 725-5018 or visit


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