Lol, yes in general it is best to avoid anything over 5g per 100g sugar, but you have to use some common sense on this. The sugar in tomatoes is a natural sugar and so breaks down very differently to refined sugars. You are very unlikely to dump on moderate amounts of natural sugars. That said, things like fresh orange juice is full of natural sugars and does cause dumping in most people if you have more than say half a normal size glass.
With tomato purée, you aren't going to be sat down eating the whole tube, it will be cooked into a big batch of mince, so the actual volume of purée you eat in a portion of bolognaise is small. Consequently the amount of sugar per portion is small too.
You can follow your dieticians advice but it means you are likely to experience dumping on a fair few occasions while you find what is ok for you and what isn't. Dumping is a horrid thing so most people try to avoid it by watching the food contents. Also, you may find that you dont dump or atleast not very easily and that can open the door to making bad food choices.
Sent from my iPhone using Forum Runner