Meta Analysis of Nutritional Studies on Vegetarians

In 1954, Hardinge and Stare13 compared the nutritional status of strict vegetarians (vegans) and lacto-ovo vegetarians with non-vegetarians of southern California. No differences in height were reported, but vegetarians and especially vegans weighed about 10 kg less than the non-vegetarian counterparts. Since the publication of this landmark research, scores of similar small studies have been conducted comparing vegetarians from many countries with their non-vegetarian counterparts.14 Evidence from these small-sample-size studies of vegetarians indicates that BMI values are either similar to or lower than non-vegetarians. On these types of studies, however, differences between vegetarian and non-vegetarians were most likely minimized due to the selection criteria for study participants (i.e., matching on anthropometrics, ineligibility of obese people).

Table 5.1 shows the result of a meta-analysis we have conducted using the data from 36 studies on females and 24 studies on males reported in

Table 5.1

Vegetarian Non-Vegetarian

Number of Weighted Number of Weighted Number of Studies Mean (SE) Subjects Mean (SE) Subjects P-Value

Males

Appendices D and E of The Dietician's Guide to Vegetarian Diets by Messina and Messina.14 While anthropometric parameters were not often the main outcome variables of the studies, in most cases, this information was recorded and reported. Weighted mean height, weight, and BMI for males and females were calculated using the number of participants in each study. Results, which were similar for males and females, showed no significant difference in height between vegetarians and non-vegetarians. However, vegetarians had significantly lower weight and BMI scores. Overall, male vegetarians compared more favorably with male non-vegetarians than female vegetarians did with their non-vegetarian counterparts. The mean weight for male vegetarians was 7.6 kg less than non-vegetarians, while for females the difference was 3.3 kg. Vegetarians — both males and females — on average, had a two point lower BMI score than non-vegetarians.

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