Prufrock, yes, you are right. Flavour is said to go into the breastmilk and I think there are experiments which show that babies tend to stay less or more on the breast when the mother has eaten certain foods (the only experiments I am aware of are ones which used vanilla or garlic, and I can't remember which way the babies chose!!).
I don't mean that nothing gets into the breastmilk - some things do, like alcohol, and medication, and nicotine, and there has been work to show that small amounts of dairy protein get into it, too....we are talking tiny amounts, by the way, which leave the gut and then go to the bloodstream and thence to the milk.
I think that flavour molecules are very small and may be able to pass through the adult gut and into the bloodstream. My biology knowledge is now running out
My point was that fruit and veg help us - as grown up people - with constipation and keep our bowels working. The main reason they do this is because of fibre (which stays in the gut) and fruit sugars (processed in the gut) and water (would not make the breastmilk waterier!). There is no logical reason why any of this would make the baby's bowels more 'active'.
However, as I said, some people truly experience differences in their baby's behaviour or functions, and they put it down to their own diet. They might be right. It's just that there is (so far - and we don't know everything yet!) no logical reason why this should be, in many (not all) cases!
It does irritate me when I hear that HVs or others tell a mother worried about her baby not gaining weight or raising some other issue that her diet needs changing - and this is suggested before the far more likely strategies (like feeding more often)