JTA Mom--this is my understanding of the situation. Kombucha does mobilize toxins, in everyone. The key is how heavy a burden of toxic load someone is carrying, and that's a lot trickier to figure out than you'd expect. In some people
we can go 20 years merrily on our downhill slide before it becomes obvious.
Amalgam fillings are a classic cause
of detoxification problems, but they don't affect everyone equally. Not everyone with amalgams will have problems like I have, or like my kids have (due to me, they don't have amalgams) but given how compromised my health was, I felt pretty normal for a long time. The downhill slide is usually slow, so the risk for a pregnant or breastfeeding mom is that she thinks she's typical, grabs a bottle of kombucha at Whole Foods and drinks it, and then has headaches, weird mood issues, maybe vomiting if it's really bad, _while_ pregnant or nursing, and now a huge amount of toxins are circulating and getting to the kiddo.
Detoxification is a balance between what is mobilized and what we can excrete. Kombucha mobilizes more than it excretes, but in a fairly healthy person, their innate detoxification pathways are reasonably functional and although their circulating toxins may well be higher for a while, they'll feel fine and their bodies will excrete whatever was mobilized and they'll end up healthier. In a very toxic person, a LOT is mobilized and their detox pathways are, by definition, deeply compromised due to the stresses that have been on their bodies building up for years. Things like headaches, body aches, nausea and maybe vomiting are some short-term symptoms of this, but longer term issues like mood problems or an increase in digestive problems are also possible.
As for figuring out whether it would benefit an individual, that takes some detective work. I personally don't think the risk is worth the benefit for any pregnant or nursing woman, but I have two kids who got too many toxins from me, and the work (and worry) to correct that situation is significant.
I don't think that just having amalgams is enough to say no kombucha ever. My poor ability to excrete heavy metals is not average, I am particularly poor. My husband, for example, is pretty darn good, and I'd say most people are somewhere in the middle.
After that, the more health issues a person has, the more uncertainties they have about what's going on with them, the more caution they should use. I've heard of people who were concerned starting with 1 tablespoon per day for several weeks, keeping a close eye on mood issues (creeping depression or anxiety, not wanting to leave home, stuff like that). But risk tolerance and having a few ideas in your toolbox in case you start feeling bad are factors here.
But clearly most of the folks in TF, for example, that just start the stuff, they feel fine drinking an entire bottle. It's just, IMO, that the spectrum of toxicity is so wide in our society, and yet the symptoms can be subtle. That's where the warnings come from.