Pub Med, EMBASE and Up To Date databases were searched through September 22, 2014, and investigators extracted data regarding study characteristics and assessed study quality among selected randomized clinical trials.Population size, demographic (i.e., gender and age) and anthropometric (i.e., body mass index) characteristics, types of interventions, follow-up periods, and trial quality (Jadad score) were recorded.As part of efforts to reduce obesity and associated morbidity, various diets for weight reduction have been proposed.Vegetarian dietary patterns have been reported to be associated with decreased risk of type 2 diabetes, coronary heart disease, and all-cause mortality.To explore study quality, we used the Jadad score, which takes into consideration the randomization appropriateness, blinded outcome assessment, and complete description of loss to follow-up.We then examined each component of the Jadad score as our study-level factor to see whether it affected the heterogeneity of the results.
We contacted three original authors to clarify data.
We calculated weighted mean differences for identical outcome measures in the vegetarian and non-vegetarian diet groups.
We assessed heterogeneity of treatment effects in the included studies using the I-squared statistic and the chi-square test of the q statistic.
For the studies that enrolled both genders, the proportion of male subjects ranged from 13 to 52 %. Six studies recruited overweight or obese patients, five studies enrolled people with type 2 diabetes, and one study included patients with rheumatoid arthritis.
Vegan and lacto-ovo-vegetarian diets were chosen as intervention diets in eight and four studies, respectively.