Try a brand that is called Organo coffee, reason why coffee messes with your gut is because of the mold, and processing chemical in the coffee, some have heavy metals, and fermaldahide. I had problems too, and heart burn and switched and now I can have black coffee with out problems.
check it our
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I went down that rabbit hole a few years ago after hearing about mycotoxins from mold. I watched a JRE podcast where the guy talked about it. Most of the studies I found that said mycotoxins were a prob were observational studies which are not very strict and do not take into consideration many factors. On the flip, randomized clinical studies I looked at found mycotoxins from mold in everything from coffee to fruit juice ect. BUT...it was at such a low level it posed no problem for 99.9% of people. Those folk very susceptible to them or that had severe health probs that were exacerbated by anything were at risk but for the majority our body can handle a wee bit of toxins.
We do it every day. When you go outside in a crowded you breathe in high amounts of all sorts of petroleum toxins. After a rain you breathe in massive quantities of spores from fungus and mold.
I say this not to be argumentative but it really kind of freaked me out. In randomized controlled studies coffee has been shown to be very good for you. 15% lower risk of cancer and heart disease, helps with high blood sugar (minimally). Lower risk of dementia and Alzheimer's, and a potent anti inflammatory.
I too had probs with heartburn. Oddly dark roast coffee has less irritating acids than medium or blonde roast from what I read and I can drink it black with no probs. Milk helps and my mom uses a tiny bit of baking soda which does somewhat change the flavor or texture or something to me.
Now back to original topic.
I tried the cacao coffee. I wanted one without sugar or added fat as I like black coffee. I also like bitter. It was not pleasant for me. I mixed it half and half with coffee and that was pretty good. My wife loved it with whole milk and stevia, but that just tasted like a dark hot chocolate.
Also tried the mushroom coffee, I liked it. Not as much as coffee but it was good and shrooms are good for you i think. But I am cheap and it is about 2-3X $ as much as regular coffee.
Sorry for the long post. I love coffee, I look forward to it every day, so I geek out a wee bit.