Fig. 1
![Fig. 1](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs12937-020-00592-2/MediaObjects/12937_2020_592_Fig1_HTML.png)
Flow diagram of study screening and selection process. The search of database and other sources identified 905 potentially relevant studies after duplicate exclusion. In addition, 897 studies were excluded after further evaluations. Finally, 8 studies were selected for this meta-analysis