Do weight loss and adherence cluster within behavioral treatment groups?
Funding agencies: This study was supported by the Department of Health and Human Services through the following cooperative agreements from the National Institutes of Health: DK57136, DK57149, DK56990, DK57177, DK57171, DK57151, DK57182, DK57131, DK57002, DK57078, DK57154, DK57178, DK57219, DK57008, DK57135, and DK56992. The following federal agencies have contributed support: National Institute of Diabetes and Digestive and Kidney Diseases; National Heart, Lung, and Blood Institute; National Institute of Nursing Research; National Center on Minority Health and Health Disparities; NIH Office of Research on Women's Health; and the Centers for Disease Control and Prevention. This research was supported in part by the Intramural Research Program of the National Institute of Diabetes and Digestive and Kidney Diseases. The Indian Health Service (I.H.S.) provided personnel, medical oversight, and use of facilities. The opinions expressed in this paper are those of the authors and do not necessarily reflect the views of the I.H.S. or other funding sources. Additional support was received from The Johns Hopkins Medical Institutions Bayview General Clinical Research Center (M01RR02719); the Massachusetts General Hospital Mallinckrodt General Clinical Research Center (M01RR01066); the University of Colorado Health Sciences Center General Clinical Research Center (M01RR00051) and Clinical Nutrition Research Unit (P30 DK48520); the University of Tennessee at Memphis General Clinical Research Center (M01RR0021140); the University of Pittsburgh General Clinical Research Center (M01RR000056 44) and NIH grant (DK 046204); the VA Puget Sound Health Care System Medical Research Service, Department of Veterans Affairs; and the Frederic C. Bartter General Clinical Research Center (M01RR01346). The following organizations have committed to make major contributions to Look AHEAD: Federal Express; Health Management Resources; Johnson & Johnson, LifeScan Inc.; Optifast-Novartis Nutrition; Roche Pharmaceuticals; Ross Product Division of Abbott Laboratories; Slim-Fast Foods Company; and Unilever.
Disclosure: The authors declared no conflict of interest.
Weight loss programs are often conducted in a group format, but it is unclear whether weight losses or adherence cluster within treatment group and whether characteristics of the group (e.g., size or homogeneity) affect outcomes. We examined these questions within Look AHEAD, a multicenter study of the effects of an intensive lifestyle intervention (ILI) in overweight/obese individuals with type 2 diabetes.
Weight losses and adherence (attendance, use of meal replacement products, and minutes of activity) were examined over one year of intervention in 2329 ILI participants in 209 treatment groups, which all received the same weight loss program.
Weight losses did not cluster among members of a treatment group (intra-class correlation [ICC] of 0.007), whereas measures of adherence had small/moderate clustering (ICCs of 0.05-0.11). The 209 groups varied in weight losses, with a mean of 8.64% (SD = 2.35%, interquartile range = 6.82%, 10.32%), but neither size nor baseline homogeneity of members affected the outcome.
Although these findings suggest that it may not be necessary to control for clustering in behavioral weight loss studies, they also indicate that merely treating individuals in groups is not sufficient to harness social influences on weight loss.