I've never heard of any bioavailability problems with either DIM or I3C and I've researching them for years.
Sorry I don't just say things without backing stuff up, I can help you research if you like. I wrote a long article recently about anti-estrogens, and often get students to do studies on them after my lectures.
"Despite the fact that DIM is stable under acidic conditions (Grose and Bjeldanes, 1992), the administration of DIM to female Sprague-Dawley rats by the i.p. route resulted in greater induction of the cytochromes P450 responsible for estradiol 2-hydroxylation as compared with the oral route (Jellinck et al., 1993). Attempting to augment DIM bioavailability, a patented formulation of DIM has been developed [BioResponse-DIM (BR-DIM); Indolplex] that utilizes solubility-enhancing microencapsulation technology.
crystalline DIM was found to exhibit low apparent oral bioavailability, as would be expected from its low aqueous and lipid solubility.
It also needs to be active for longer periods to work as it breaks down very quickly as shown above, in 1 hour it declines in its effects.
Oral route shows less affect on estrogen than i.p
The bio response formula that initiate greatest results was a topical application with the following.
DIM, 3,3′-diindolylmethane; DMSO, dimethyl sulfoxide
Because it lacks bioavailability researchers have been looking for ways to improve it in oral form, so heres from another study.
"DIM formulations on the basis of pegylated vitamin E are known in prior art (U.S. Pat. No. 6,416,793 published on Jul. 9, 2002). TPGS-based compositions, though, have helped achieve a very insignificant (not more than 50% to 100%) increase in biological availability of DIM, its analogues, and derivatives, for which reason the therapeutic potential of these compounds cannot be used to capacity. Besides, the preparation has to be spray-dried in a very power-intensive process that raises its production costs.
The closest prior art of the present invention described in international application WO 2009032699 (published on Mar. 12, 2009) relates to pharmaceutical compositions based on an anti-proliferative combination of DIM, polyunsaturated fatty acids (PUFAs), and folic acid. These compositions are disadvantageous because they are not stable enough, the principal component precipitating as tiny crystals in storage. Moreover, most people being short of omega-3 fatty acids, derived PUFAs may only have exaggerated effects. According to recent findings, addition of folic acid is undesirable for small children having inflammatory diseases of the autoimmune type
Indole which as I said is a great product, has much higher oral bioavailability.