To evaluate the impact of the interaction between diet type as part of the standard behavior therapy and treatment preference on weight loss at eighteen months.

• 18 to 55 years of age
• Body mass index (BMI) between 27 and 43
• Willingness to be randomized to one of two treatment groups: Standard behavior therapy or standard behavior therapy with ovolactovegetarian education
• Successfully complete a five-day food diary.

• Serious illness or unstable condition for which physician supervision of diet and exercise prescription was needed
• Cardiovascular or orthopedic condition that would require physician clearance before participation
• Limited exercise capabilities
• Pregnant or intending on becoming pregnant in the next 18 months
• Current treatment for psychological disorder
• Reported alcohol consumption of greater than four drinks per day
• Concurrent or previous participation in a weight loss treatment program or used weight loss medication
• Reported no regular intake of meat, fish and fowl
• History of serious binge eating problems
• Did not at least moderately prefer one of the dietary treatments (standard behavior therapy or standard behavior therapy with ovolactovegetarian component) over the other.

Recruitment

• Contacting individuals seeking weight loss treatment and listed in the University of Pittsburgh's Obesity Nutrition Research Center database
• Placing an audio advertisement on the University and Medical Center's Audix announcement systems
• Mailing recruitment cards to individuals on purchased address lists.

Design

Initial subjects were screened for eligibility by phone. If the subject met criteria, he or she received a screening packet in the mail. Once the packet was completed the subject was invited to an information session and baseline assessment in which subjects were given a five-day food diary to complete. Upon return of the diary and meeting all the inclusion criteria, the subjects were randomized into the study. 

Diet

During randomization, subjects were initially randomized to treatment preference "yes" or "no" with a three-to-two probability. After this, the subjects were randomized again into either the standard behavior treatment or standard behavior treatment with ovolactovegetarian component. All subjects were instructed to restrict consumption of calories (1,200 to 1,500 for women and 1,500 to 1,800 for men) and fat (25% of total calories). Subjects in the ovolactovegetarian group were asked to record the number of meat meals eaten every day. 

Behavioral Therapy

Subjects received 32 treatment sessions of standard cognitive behavioral therapy for weight management over a period of 12 months, including: Self-monitoring eating and exercise behaviors, goal setting, cognitive restructuring, stimulus control, demonstrations and skill development. The sessions were identical except for information on the two dietary plans. 

Physical Activity

It was recommended to the subjects to increase physical activity to 150 minutes per day. [Note: Article later states physical activity recommendation of 150 minutes per week.]

Subjects were instructed to record their daily food intake and physical activity in minutes and these diaries were used as indicators of adherence to the intervention protocol along with attendance at the treatment sessions.

Laboratory and Physical Assessments

Laboratory assessments included lipid profile, serum glucose and insulin measurement (taken at baseline, six, 12 and 18 months). Physical measurements included height, weight, waist circumference and blood pressure. Subjects were weighed before each treatment session.

Intervention

Standard behavior therapy with an ovolactovegetarian diet.

Statistical Analysis

Only data from baseline to six months is included in the article. To assess differences between the dietary treatment groups and between standard behavior therapy with ovolactovegetarian component groups, chi squared tests were performed for categorical data. For continuous variables, T-tests were used for normally distributed variables and Mann-Whitney tests were used when the variables were not normally distributed.

Timing of Measurements

Outcome variables were measured at baseline and at six, 12 and 18 months. Treatment sessions were held weekly for the first six months, then every two weeks for months seven to nine and monthly for months 10 to 12. At 12 months, subjects entered the maintenance phase until the 18-month assessment appointment. 

Dependent Variables

• Anthropometric measurements (weight, waist circumference, blood pressure)
• Blood serum values (total cholesterol, HDL, LDL, triglycerides, serum glucose and insulin). 

Independent Variables

• Standard Behavior Treatment
• Standard Behavior Treatment in conjunction with ovolactovegetarian diet.

• Initial N: 200 at randomization
• Attrition (final N): 182 (91%)
• Age: Average age, 44.1±8.6 years
• Ethnicity: Mainly Caucasian, though sample had 29.7% minority representation
• Other relevant demographics: Only 12.6% of subjects were men
• Anthropometrics: Baseline weight average 94.86kg±14.58kg
• Location: Pittsburgh, Pennsylvania.

• All subjects who preferred ovolactovegetarian diet were assigned to that group
• Only fifty percent of those who chose the standard behavior treatment were randomly selected for inclusion
• Guiding the participants in adopting the ovolactovegetarian diet took many forms, including slow elimination of meat over the first six weeks of the study.  

Changes from Baseline to Six Months

For the entire sample, significant changes were observed at six months in all measures except LDL-C and glucose. Comparing diet groups:

• Vegetarian diet subjects had significantly lower protein intake (P<0.001) and significantly higher carbohydrate intake (P=0.013) compared to the omnivore diet
• LDL-C levels were significantly different between diet groups at six months (see table below).  

Baseline and Change Measurements and Comparisons of Change Scores by Diet Group after Six Months

Sex (male) and marital status were the only demographic characteristics significant with compliance in the standard behavior treatment with ovolactovegetarian component.

Baseline and Change Measurements and Comparisons of Change Scores of the Ovolactovegetarian Participants by Adherence Group after Six Months

Subjects in both diet groups benefited from the first six months of the behavioral intervention in that they reduced their weight by greater than 7%, which results in clinically significant improvements. Subjects who were adherent to the ovolactovegetarian diet experienced significant improvements in several physical and biological outcome measures.