Daidzein and genistein are abundant in soy-rich foods, whose supplementation has been proposed to have beneficial effects on several diseases, including diabetes mellitus and obesity. 17β-estradiol (E2) enhances the expression of the Slc2a4 gene and GLUT4 protein in adipose tissue, increasing glucose consumption and contributing to glycemic control. We investigated, in 3T3-L1 adipocytes, the effect of low and high doses of daidzein and genistein on Slc2a4/GLUT4 expression and the participation of estrogen receptors 1/2 (ESR1/ESR2) in the regulations observed. Differentiated adipocytes were cultivated, for 24 h, in the presence of 17β-estradiol (E2, 10 nM), daidzein (10 nM–150 μM) and genistein (10 nM–50 μM), with or without ESR1 or ESR2 antagonists. Daidzein/genistein at a low dose (10 nM) increased Slc2a4/GLUT4 expression (50%, p < 0.05), an effect abrogated by an ESR1 antagonist, mimicking the effect of E2. However, maximal doses of daidzein and genistein reduced, in a ESR1-mediated mechanism, the expression of mRNA (by 47% and 60%, p < 0.001) and the protein (by 29% and 36%, p < 0.01), respectively, for daidzein and genistein, as compared to E2. In conclusion, in adipocytes, daidzein and genistein have a biphasic ESR1-mediated effect: while low concentrations increase the expression of Slc2a4/GLUT4, high concentrations decrease it, the former predisposing to an adipogenic effect, the latter to a diabetogenic condition.