Soy is used as a filler in NEARLY ALL "low carb" processed food and in most "energy" bars. The ingredient to avoid is "soy protein isolate" which as far as I can tell is indigestible for humans. It definitely gives ME a stomach ache. I avoid this stuff and check for it in any powders that I might add to a smoothie. The cheapest and best protein additive for smoothies is whey---IF you are not allergic to milk.
I just ran across a succinct list of the reasons to avoid soy at the Weston A Price Foundation website. There are also links here to the research papers themselves, if you're interested. Bottom line: if you're going to eat soy, don't eat it with every meal, and avoid TVP at all times. That shit's toxic. DON'T consider it a meat substitute. If you don't eat meat, eat cheese and eggs to get the amino acids and fats you need.
I do still eat edamame, which is fresh green soybeans sucked from the hull, raw or lightly steamed. Not with every meal! But good sometimes with sushi.