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

Abstract

Background: With obesity rampant, methods to achieve sustained weight loss remain elusive. Objective: To compare the long-term weight-loss efficacy of 2 cal and fat-restricted diets, standard (omnivorous) versus lactoovo-vegetarian, and to determine the effect of a chosen diet versus an assigned diet. Design, subjects: 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-ovovegetarian 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. Measurements: Percentage change in body weight, body mass index, waist circumference, low-and high-density lipoprotein, glucose, insulin and macronutrient intake. Results: The program was completed by 132 (75%) of the participants. At 18 months, mean percentage weight loss was greater (P ¼ 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. Conclusions: 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.

Vegetarian Diets and Weight Reduction: a Meta-Analysis of Randomized Controlled Trials

“…The design of nonvegetarian diets varied across studies and included low-fat, anti-diabetes, lipid-lowering, and weight reduction recipes. Of the six studies that applied energy restriction, five applied the restriction to both the intervention and control arms, 8,[10][11][12]16 while one study designated 1 week of energy restriction solely to the intervention arm. 23 Among the remaining six studies without energy restriction in the intervention arms, one adopted energy restriction in their control groups who were overweight.…”

“…The means and standard deviations of weight change were obtained from all studies. For articles that did not report standard deviations, 10,17,19 we imputed a change-from-baseline standard deviation using a correlation coefficient of 0.96 estimated from trials 9,11,12,14,16 with available data based on Cochrane's formula. 21 For three studies 9,11,15 with repeated measurements during the follow-up periods, we collected results at the 1-year time point.…”

“…6 The two major types of vegetarian diets are the lacto-ovovegetarian diet, in which meats are avoided but consumption of milk and eggs is allowed, and the vegan diet, in which all products originating from animals are avoided. Thus far, the results of randomized clinical trials [7][8][9][10][11][12][13][14][15][16][17][18][19] investigating the affect of vegetarian diets on weight reduction have been inconclusive, which could be due to the diverse populations, small sample sizes, different intervention durations, and poor adherence. As there have been no studies with large sample sizes, we performed a meta-analysis of randomized clinical trials conducted to date in order to compare the effect of vegetarian diets with that of non-vegetarian diets on weight reduction in the general population.…”

Effect of Allowing Choice of Diet on Weight Loss

“…In the Paving the Road to Everlasting Food and Exercise Routine (PREFER) study, 176 participants with at least a moderate preference for either an LFD or a lacto-ovo-vegetarian (LOV) diet were randomized to a choice or no choice condition (36). Participants in the choice condition lost less weight (−3.9% and −5.3% for chosen LFD and LOV diet, respectively), than those assigned a diet (−8.0% and −7.9% for assigned LFD and LOV diet, respectively; p=0.02 for study arm by time interaction).…”

“…23 (12) 13 (7) 21 (10) 15 (8) 36 weeks 24 (13) 12 (4) 22 (10) 15 (9) 48 weeks 25 (14) 12 (5) 21 (10) 17 (12) Saturated fat, % daily kcal Baseline 66 (30) 63 (26) 88 (60) 12 weeks 62 (33) 43 (22) 67 (34) 61 (34) 24 weeks 59 (34) 46 (23) 53 (27) 51 (27) 36 weeks 62 (36) 44 (15) 55 (25) 54 (28) 48 weeks 61 (34) 43 (20) 53 (27) 55 (31) Protein, % daily kcal Estimated mean weight trajectories in kg over 48 weeks for the Choice and Comparator arms from linear mixed models. Table 1 Baseline participant characteristics (11) 54 (11) 55 (10) 49 (13) 55 (10) 57 (10) 47 ( 109 (21) 109 (22) 108 (16) 108 (19) 107 (19) 112 (22) Body mass index, kg/m 2 36 (6) 36 (6) 36 (7) 35 (4) 36 (5) 36 (5) 37 ( 46 …”