When we live with a dog or any other domestic animal, we have to know that there are a series of foods that should not be eaten, since otherwise their health could be in danger. But we must also know that there are some myths that are just that, myths, that do not correspond well with reality.
So if you're wondering why dogs can't eat tomato, the answer is that they can eat. Simply, do not abuse.
Tomato is not bad for dogs. If one day we have leftover macaroni or spaghetti, for example, we can give it to them without problem, even if it has salt. For one day a week nothing is going to happen to him. However, what we should never do is give them tomatoes every day, much less give them green. Likewise, we do not have to feed the leaves or the stem either.
In the event that we have a vegetable garden or that we are growing tomatoes in pots, we have to watch our friend so that he does not eat them, mostly out of precaution. Anyway, I insist, to make him feel bad he would have to eat huge amounts of leaves and tomatoes, and no one would think of giving his dog a kilo of tomato for example, and less every day.
With respect to human tomato sauce and ketchup, by carrying salt and sugar, yes you have to be more alert. But for that we can simply make a sauce with natural tomatoes and not add salt or sugar.
In case you have eaten more, the dog may have diarrhea, tiredness, stomach pain, and muscle weakness. For him to improve, we will have to take him to the vet urgently.
Thus, we can give you ripe tomatoes (better if they are natural) from time to time, but never green.