• The purpose was to determine independent and combined effects of treatment preference and a standard behavioral treatment program with a calorie- and fat-restricted ovolactovegetarian diet (LOV-D) compared with a calorie and fat-restricted standard omnivorous weight loss diet (STD-D) on weight, serum lipids, insulin resistance and macronutrient intake in overweight and obese adults
• To examine whether the above outcomes differed among those who adhered to the vegetarian diet compared to those who did not.

• Age between 18 and 55 years
• Body mass index (BMI) of 27kg/m² to 43kg/m²
• Willingness to be randomly assigned to one of two treatment preference conditions and one of two dietary conditions
• Successful completion of a five-day food diary
• Willingness and ability to provide informed consent
• No current medical condition requiring physician supervision of diet or physical activity
• No physical limitation restricting exercise ability
• Not pregnant or planning to become pregnant during 18 months of study
• No current treatment with a medication that might affect weight
• Alcohol intake not exceeding four drinks per day
• No participation in a weight-loss program or use of a weight-loss medication within six months before study enrollment
• Reported consumption of meat, poultry or fish in the past month.

• Participants were ineligible if they did not meet the inclusion criteria above
• Participants were disqualified if they selected an equal preference for two dietary options
• Fasting plasma glucose concentration was used to screen for exclusion criterion of diabetes.

Recruitment 

Mode of recruitment included mass mailings from purchased lists; a database of persons seeking weight-loss treatment; and telephone announcements to staff, students and faculty at the University of Pittsburgh and University of Pittsburgh Medical Center. 

Design

• Randomized clinical trial
• Two-times-two factorial experimental design was used, which resulted in four group assignments:
  • Preference: Yes + LOV-D
  • Preference: Yes + STD-D
  • Preference: No + LOV-D
  • Preference: No + STD-D.  

Blinding Used

• Staff entering dietary intake data were blinded to the treatment group and assessment period
• Personnel taking the blood samples were blinded to treatment group.

Intervention

• Dietary intervention: For participants weighing less than 90.5kg at baseline a diet of 1,200kcal per day was prescribed for women and 1,500kcal per day for men. For those weighing more than 90.5kg at baseline, a diet of 1,500kcal per day for women and 1,800kcal per day for men was prescribed. Participants were also encouraged to reduce fat intake to 25% of total energy.
• Physical Activity: Participants were encouraged to engage in at least 50 minutes of physical activity per week with gradual increases to at least 150 minutes per week by week six of the study and thereafter
• Group sessions: Which focused on modifying eating and physical activity behaviors, as well as food tastings and skill-building exercises, were undertaken as follows: Weekly for the first six months; biweekly session for months seven through nine; and monthly for months 10 through 12. Sessions were held separately for the two dietary treatment groups.
• Diaries: For dietary and physical activities were completed and by participants and submitted at treatment sessions. 

Statistical Analysis

• ANOVA, Kruskal-Wallis test, chi-square analyses, Fisher's Exact tests were used to compare preference groups and diet groups with participants' characteristics and response variables at baseline
• Exploratory data analysis methods
• Full factorial with PROC mixed models used to express change from to baseline for variables such as TG, cholesterol and weight
• Wilcoxon signed-rank test was used for change in physical activity over time
• Sobel test used to examine the potential mediation effects of physical activity on biochemical outcomes.

Timing of Measurements

Baseline and at six-, 12- and 18-month intervals.

Dependent Variables

• Anthropometrics: BMI (weight in kilograms; measured at baseline and repeated every six months until the final 18-month visit). Weight was obtained after an overnight fast in light clothing, without shoes. Equipment used was the Tanita bioelectrical impedance scale. Height was measured using a wall-mounted stadiometer.
• Biochemical measurements: Total cholesterol, HDL, LDL, TG, serum glucose and insulin concentrations were measured from blood drawn after a 12-hour overnight fast. Glucose concentrations were measured using hexokinase-glucose-6-phosphate dehydrogenase enzymatic assay; insulin measured by radioimmunoassay kit; total, cholesterol, HDL-cholesterol and triacylglycerols were measured enzymatically on an Abbott Super System auto analyzer; LDL-cholesterol was estimated using Friedewald equation for participants with TG concentrations less than 400mg per dL, but automated spectrophotometric assay was used for participants whose TG concentrations were more than 400mg per dL 
• HOMR-IR  was calculated as fasting insulin concentration.

Independent Variables

• Diet: Two calorie- and fat-restricted dietary options based on preference. Group one was the standard diet (STD-D) and group two the ovolactovegetarian diet (LOV-D). Each option had two groups (Yes and No). Diets were collected via food records and analyzed using a nutrition data system software.
• Energy expenditure during physical activity for periods of seven days were measured using Paffenbarger Activity Questionnaire from self-reported data.

Initial N

• 200 participants attended baseline assessment; nine were ineligible, 15 were discarded. A total of 176 were assigned to four groups.
• 86.93% females; N=153 and N=23 males.

Attrition (Final N)

N=132; 75% of participants completed the 18-month assessment.

Age

Mean age, 43.3±9.0 years to 44.9±8.5 years.

Ethnicity

70.5% white; no other ethnic categories were reported.

Other Relevant Demographics

• Employment: 93.18%
• Marital status: 63.06% married or lived with a partner.

Anthropometrics

• Baseline weights: 67.62kg to 136.28kg
• Mean BMI: 34.02±4.09.

Location

University of Pittsburgh and Pittsburgh Medical Center, Pittsburgh, Pennsylvania, US.

Diet Adherence

• Two levels of adherence to the ovolactovegetarian diet (LOV-D) were used: 100% adherence or less than 100% adherence
• At six, 12 and 18 months, 61%, 53% and 36% reported complete adherence (100%) to the LOV-D, respectively
• A significant main effect for adherence was found for total cholesterol (P=0.04) and HOMA-IR (P<0.01) at six months, but no significance for those variables were seen at 12 and 18 months
• Participants who adhered to the LOV-D had lower intake of energy (P<0.01), total fats (P<0.01) and monounsaturated fats (P<0.01) at six months than individuals who reported intakes of meat, poultry or fish. The differences for total fats were marginal at 18 months (P=0.05), but remained significant for monounsaturated fats at 18 months (P=0.02).

Other Findings

• Average amount of energy expenditure reported at baseline (median reported)
  • Preference Yes+STD-D: 1,556.00kcal
  • Preference Yes+LOV-D: 1,344.00kcal
  • Preference No+STD-D: 1,432.50kcal
  • Preference No+LOV-D: 954.00kcal.
• At 18 months, the self-reported energy expenditure increased
  • Preference Yes+STD-D, 2,214.50kcal
  • Preference Yes+LOV-D, 1,904.00kcal
  • Preference No+STD-D, 2,222.50kcal
  • Preference No+LOV-D, 2,323.00kcal
  • No significant differences across groups (P=0.52).
• Physical activity was found to have a direct effect on weight change (P=0.01)
• Physical activity had a total effect (P<0.01) on total cholesterol values (controlling for weight change). Observations were made at zero to 12 months.
• Physical activity had a direct effect on total cholesterol (P=0.02). Observations were made at zero to 12 months.
• Physical activity had a total and direct effect (P<0.01) on HOMA-IR at six months only
• The effect of physical activity on LDL:HDL cholesterol and TG was mediated through weight loss.

• Findings did not show that adopting a LOV-D results in significantly improved biochemical measures or dietary patterns than does STD-D, maybe due to the fact that the LOV-D group did not strictly adhere the prescribed diet overtime
• All participants reduced their total energy and fat consumption and increased physical activity
• Based on previously reported data, the data suggest the LOV-D led to substantial short-term cardiovascular health benefits. (Data was not included in this article.)
• Compliance to LOV-D was a challenge over time, which declined to 36% by the 18th month; therefore, findings suggest that strategies are needed to improve long-term adherence to the LOV-D plan so as to achieve the true effects of the intervention and clinical outcomes
• Study results refute the notion that allowing participants to choose treatment results in favorable outcomes
• Providing a study participant his or her preferred choice of treatment does not necessarily lead to improved adherence or improved outcomes
• Limitations include declining compliance to the LOV-D diet over time, thereby limiting the authors' ability to detect differences between the dietary groups; three-day food record may not represent dietary intake throughout the study; under-reporting of energy and fat intakes may be common; underrepresentation of men is also a limitation
• Neither a LOV-D nor treatment preference, individually or in combination, resulted in significant effects on total cholesterol, LDL:HDL cholesterol, HOMA-IR, or energy and macronutrient consumption in the study population
• Results should be interpreted with consideration of the declining adherence in abstaining from meat, poultry and fish in the LOV-D group by the 18-month assessment
• Overall, participants benefited from their participation with improvements in dietary and physical activity measures that were reflected in improved body weight.

• Strengths: Randomized clinical trial; accounted for dropouts by using intention to treat analyses
• Concerns: Sample sizes, especially for the vegetarian group, declined to the point where it affected effect size and consequently generalizability
• Other relevant data such as changes in BMI over time and waist circumferences were mentioned but data were not shown
• Other macronutrients data such as protein and carbohydrate were not provided as part of the analysis. This is crucial in interpreting the results of weight loss. It is difficult, therefore, to say what proportion of the diet was carbohydrate or protein or the source of protein for the LOV-D groups.
• Study's outcome will be greatly improved if diet prescription was more tightly controlled; a three-day diet record, in my mind, may affect reported outcomes.