Composition of the soy diets
To find out how soy isoflavones and androgen levels are related, the authors conducted two experiments. In the first experiment, rats in the treatment group were given soy flour with their normal chow. In the second experiment, rats in the treatment groups were given either a soy methanol extract or semipurified soy isoflavones.
The isoflavone content of the soy flour was 1.92 mg/g. The isoflavone contents of the soy methanol extract and semipurified soy isoflavones were 3.38 mg/g and 218 mg/g, respectively. In the first experiment, the rats in the treatment group received 442.7 g/kg soy flour in their diet. In the second experiment, they received 20 g/kg of soy extract or 2 g/kg of soy isoflavones in their diets.
Long story short, the according to the authors, the actual soy isoflavone intakes of the rats were as follows: 19 mg/day in the soy flour group, 0.9 mg/day in the soy extract group, and 3.3 mg/day in the soy isoflavone group. The control groups consumed zero soy isoflavones.