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.e. 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 (e.g. Lactococcus, Terrisporobacter, and Butyribacter) significantly differed between the SPC diets and the CAS diet regardless of isoflavone level and time, whereas the abundance of other genera (e.g. Lachnospiraceae ND3007 and Akkermansia) 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.