The health benefits of soy foods are attributed to the high-quality
protein and the bioactive compounds such as
isoflavones. We previously reported that feeding obese (fa/fa) Zucker rats
soy protein concentrates (SPCs) with low
isoflavone (LIF) and high
isoflavone (HIF) for 9 weeks significantly reduced
liver steatosis compared to a
casein control (C) diet. The current study extended the dietary treatments to 18 weeks to investigate the long-term effect of LIF and HIF SPC diets. 6-week-old male lean (L, n = 21) and obese (O, n = 21) Zucker rats were fed a
casein C diet, LIF and HIF SPC diets for 18 weeks and
body weight (BW) was recorded twice weekly. Rats were killed after 18 weeks to measure
liver steatosis and serum
aspartate aminotransferase and
alanine aminotransferase. Obese rats had significantly greater final BW, liver weight, liver weight as the percentage of BW, and steatosis score compared to lean rats in all three dietary groups. The obese high-
isoflavones (OHIF) group had significantly higher BW compared to obese control (OC) group (P < .0001) and obese low-
isoflavones (OLIF) group (P = .01). OC group had significantly greater liver weight, liver weight as the percentage of BW, and
liver steatosis score compared to OLIF (P = .0077, P < .0001 and P < .0001, respectively) and OHIF (P = .0094, P < .0001, and P < .0001, respectively) groups. Taken together, long-term feeding of SPC diets protected against
liver steatosis regardless of
isoflavone levels.