You shouldn't eat too many eggs, milk and cheese if you have stomach problems. It's not good for your organism.
It's one of those errors I have heard more than once but, for some reason, I just couldn't remember the correct word. It then took a bus journey this morning to finally realise what the word was. And goodness knows why I didn't think of it before.
In the Polish language, organism is spelt organizm, and the word on its own has the same meaning as in English: a small living animal or plant, usually too small to see under a microscope. So if we literally interpret the sentence, it suggests that the listener has been giving their very, very tiny pet too many dairy products.
The problem is that when it becomes part of the longer noun phrase organizm czlowieka, this then means the human body.
The word that our speaker is looking for, and best fits the context of the example, is most likely to be metabolism, the meaning being the way that the chemical processes in your body cause food to be used in an efficient way - usually to break it down and absorb its nutrients. And I believe the word is similar to Polish.
If, of course, the context was different, such as Eating too much is not good for your body, then this would make sense.