guggulsterones are promiscuous steroid receptor ligands. they are antagonistic of the androgen receptor, strongly agonistic of the progesterone receptor and weakly agonistic of the estrogen receptor.
there is no evidence they have any impact on thyroid as claimed and their impact on cholesterol has been discredited, with recent studies showing a mild increase in cholesterol.
IMHO they are too be avoided for fat loss and bodybuilding purposes.