Comparison of the Atkins, Ornish, Weight Watchers, and Zone Diets for Weight Loss and Heart Disease Risk Reduction: A Randomized Trial Melody Lee, MD UCSF Family and Community Medicine Journal Club January 21, 2005 Introduction: Context Obesity has become an epidemic Introduction: Context
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Melody Lee, MD
UCSF Family and Community Medicine
January 21, 2005
Assess the effectiveness of four popular diets for weight loss and cardiac risk factors, and to assess self-reported adherence rates to each diet
Q: Can I apply it to my clinic population?
A: Probably. The participants in this study are not medically dissimilar to patients in our clinics and the study is realistic. However, participants who called likely more motivated than typical patient. Study did not report SES, language, ethnicity, etc.
Q: Are the likely benefits worth the potential harms and cost?
A: Probably. Obesity has been shown to increase morbidity and mortality and even modest weight loss has benefit. No obvious harm in the short term. Long term has not been studied. Also, does being on a diet decrease quality of life?
Q: Were all the clinically important outcomes considered?
A: Possibly. Besides weight loss and cardiac risk factors which have been shown to decrease morbidity and mortality, investigators could have examined quality of life. Mortality was beyond the scope of this study.
Q: Was the assignment of participants to intervention random?
A: Yes, a computer generated a diet to each small group and at only one of 4 meeting times
Q: Was follow up complete?
A: No. This study drop out rate was large at 42% (consistent with dropout rates in other diet studies). Data was analyzed with the assumption was that those who discontinued would be back to baseline and missing data was substituted with baseline. This is a very conservative measure. Results were consistent when missing data was excluded entirely from the analysis
Q: Were patients analyzed in the groups to which they were randomized?
A: Yes, this study followed the intention to treat principle
Q: Were participants, clinicians and personnel blinded to the intervention?
A: No, participants and providers knew which diet they were assigned by the first meeting, which could have affected outcomes depending on expectations, biases. (those optimistic about the diet they’ve been assigned may do better) Only the lab personnel was blinded, the person least likely to affect outcome.
Q: Were the groups similar at the start of the trial?
A: Yes: demographically, as well as by baseline weight, caloric intake and cardiac risk factors
Q: Were the groups treated equally apart from their intervention?
A: Maybe. Investigators standardized their recommendation for daily MVI, 60 minutes of exercise/ week, and avoiding commercial support. However they did give each participant the corresponding literature and cookbooks, which are different from one another. Also, there was no mention of standardized small group meeting content or structure
Q: How large and precise was the treatment effect?
A: Results were only modest in weight loss and improvement in cardiac risk factors, but statistically significant.