I often go on Missions trips to different countries and this is something that happens to me all the time. So, this is my rule of thumb…It may not be right but it’s how I get by.
To me, it all depends on the level of relationship I am attempting to establish with the individual offering. If I’m simply passing through and I will likely never meet this person again and they’ve offered me something, the answer is a gracious, “You are so kind but no thank you.” I may add that I’ve already eaten.
However, if I’m trying to establish a relationship or I’ll be spending a lot of time with someone and they’ve offered me something that I’m not sure I can handle, I say “I’m a little full but I’ll try a little” and I really emphasize “a little”. I may even feign interest that I’d like to see this fascinating dish and I’ll ask them about the dish to find out the ingredients. But my real motives are to follow them to the pot/container and see what they’re serving and also be able to regulate how much they put on my plate. And then yes, I eat what they give me but then it would only be a small portion that a swig of water or a drink can easily wash away should it not be to my liking. And if I do like it, I can ask for more.
In either case, your facial expression is key. Try not to reveal your anxiety to trying their local food that much. I find that a poor expression is more offensive that the actual refusal of what they’re offering.
I hope that was helpful.