Search results and overview of included studies
Our search led to 462 relevant studies. After duplicates removing, a
wide range of screening of the titles and abstracts, the careful
assessment was performed on 454 related articles. Of these, 23 articles
remained after considering the inclusion and exclusion criteria for the
eligibility. Eventually, 18 articles, including, 14 effect sizes for
adiponectin and 14 effect sizes for leptin, which studied a total of
1042 and 1073 participants respectively and aged 28.9 – 69 years, were
identified in the current systematic review and meta-analysis. One study34 just reported
baseline data in the article paper and we did not receive raw data for
after trial data from the authors. This listed number is inclusive of
people who were dropouts in some studies. Figure 1 represents
the selection process and reasons for excluding the studies. The data inTable 1 illustrates the main characteristics of the articles in
our systematic review and meta-analysis.
In brief, the studies were published between 2009 and 2019. The duration
of these RCTs ranged between 4 weeks to 24 months. The total number of
participants who completed the studies in inclusion criteria was 511
participants in the intervention and 531 in the placebo groups for
adiponectin and 544 participants in the intervention and 529 in the
placebo groups for leptin. Soy protein have been used in a variety of
forms in these studies like soy-based meal replacement18-20,25,26,35,36,
soy powder or formula15-17,21,22,24,27,37and capsule supplement19,23,38.
However most of studies have been used soy powder or formula. The dose
of soy protein supplementation was 6 to 50 g/day among these studies.
Three studies used a randomized crossover design18,24,27,
two of them was also single blind18,27and the other study had the design of double-blind24. Among 18 studies 9
studies were conducted in n the United States15,18-21,24,25,27,36.
The effect of soy protein on both adiponectin and leptin concentration
was examined in 10 studies; and 4 studies only reported adiponectin17,18,25,38and 4 studies only reported leptin35-37,39.
Overall, 18 effect sizes were extracted from these studies for
adiponectin and leptin concentration.