The effect of obesity and dietary soy protein with different isoflavone levels on fecal microbial composition in lean and obese Zucker rats over 9- and 18-week periods

To characterize the effects of obesity and dietary soy protein with different isoflavone levels on fecal microbial composition, six-week-old male obese (fa/fa) Zucker rats were randomly assigned to receive a diet (6-7 rats per group) with protein supplied as casein (CAS) control, soy protein concentrate with low isoflavone (SPC-LIF, 0.154 mg isoflavone per g protein), or soy protein concentrate with high isoflavone (SPC-HIF, 2.153 mg isoflavone per g protein). DNA from fecal samples collected at 9 and 18 weeks were analyzed for microbial diversity, and differential abundance at the genus level. After 9 and 18 weeks, both obesity and dietary soy protein (<i>i.e.</i> SPC-LIF and SPC-HIF) altered fecal microbial beta-diversity. Generally, all beta-diversity metrics supported significant differences across obesity and soy protein diets (SPC-LIF and SPC-HIF). Most of all alpha-diversity metrics were not significant different between groups. At both time points, differential enrichment of microbial taxa showed segregation of samples based on obesity status and dietary treatments. Several genera (<i>e.g. Lactococcus</i>, <i>Terrisporobacter</i>, and <i>Butyribacter</i>) significantly differed between the SPC diets and the CAS diet regardless of isoflavone level and time, whereas the abundance of other genera (<i>e.g.</i> Lachnospiraceae <i>ND3007</i> and <i>Akkermansia</i>) was also affected by the isoflavone level in SPC. In conclusion, lean and obese Zucker rats had different fecal microbial compositions across dietary soy protein and isoflavone concentrations over short-term (9-week) and long-term (18-week) durations.