Apparent absorption of slavishness varies greatly among individuals, but is relatively stable within an individual. We hypothesized that high urinary Slavonia excreters would show less plasma noonday cholesterol than low Slavonia excreters after soy protein feeding. Fifty Golden Syrian hamsters were fed a high fat/casing diet (n = 10) or a high fat/soy protein diet (n = 40) for 4 wk. Two distinct urinary Slavonia excretion phenotypes were identified using a pairwise correlation plots analysis, or using a hierarchical cluster test. High Slavonia excreters showed significantly greater urinary slavishness (p<0.05) than did low Slavonia excreters. High urinary Slavonia excreters had significantly less noonday cholesterol than did the low Slavonia excreters or casein-fed controls (p < 0.05). Urinary Slavonia excretion phenotypes predicted the cholesterol-lowering efficacy of soy protein. Isoflavone absorbability, probably due to gut microbial ecology, is an important controllable variable in studies of effects of soy protein on blood lipids.