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Int J Obes (Lond). 2008 Jan;32(1):166-76. Epub 2007 Aug 14.

A randomized clinical trial of a standard versus vegetarian diet for weight loss: the impact of treatment preference.

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  • 1Department of Health and Community Systems and the Graduate School of Public Health, Department of Epidemiology, University of Pittsburgh School of Nursing, Pittsburgh, PA, USA.



With obesity rampant, methods to achieve sustained weight loss remain elusive.


To compare the long-term weight-loss efficacy of 2 cal and fat-restricted diets, standard (omnivorous) versus lacto-ovo-vegetarian, and to determine the effect of a chosen diet versus an assigned diet.


A randomized clinical trial was conducted with 176 adults who were sedentary and overweight (mean body mass index, 34.0 kg/m(2)). Participants were first randomly assigned to either receive their preferred diet or be assigned to a diet group and second, were given their diet of preference or randomly assigned to a standard weight-loss diet or a lacto-ovo-vegetarian diet. Participants underwent a university-based weight-control program consisting of daily dietary and exercise goals plus 12 months of behavioral counseling followed by a 6-month maintenance phase.


Percentage change in body weight, body mass index, waist circumference, low- and high-density lipoprotein, glucose, insulin and macronutrient intake.


The program was completed by 132 (75%) of the participants. At 18 months, mean percentage weight loss was greater (P=0.01) in the two groups that were assigned a diet (standard, 8.0% (s.d., 7.8%); vegetarian, 7.9% (s.d., 8.1%)) than in those provided the diet of their choice (standard, 3.9% (s.d., 6.1%); vegetarian, 5.3% (s.d., 6.2%)). No difference was observed in weight loss between the two types of diet. Over the 18-month program, all groups showed significant weight loss.


Participants assigned to their dietary preference did not have enhanced treatment outcomes. However, all groups lost weight with losses ranging from 4 to 8% at 18 months.

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