I was able to find this: https://www.sciencedirect.com/science/article/abs/pii/S0006295215003822#:~:text=The%20present%20results%20demonstrated%20that,taste%20s

I was able to find this: https://www.sciencedirect.com/science/article/abs/pii/S0006295215003822#:~:text=The%20present%20results%20demonstrated%20that,taste%20substance%20obtain%20hypoglycemic%20effect https://www.sciencedirect.com/science/article/abs/pii/S00062.... Apparently most of the effect is due to activation of the "bitter taste reception pathways" in the gut. So even though it has very low bioavailibility, it can still stimulate GLP-1 secretion just simply due to its incredible bitterness