Most brands of tomato paste don't contain any (you can see the Leggos brand on their website don't contain any added sugar).  That being said it contains of course tomatoes.  Leggos is about 6.2g sugar per 100g.  This is basically because it's concentrated so your getting more natural sugar in one hit.  That all being said, I guess it would depend on the dish your using it for.  We use the pizza sauce ones commonly (or sometimes reduce a tin of tomatoes without added sugar), one packet contains about 3.7g of sugar in total, spread that over 8 slices of pizza.  I can't imagine eating a whole wack of tomato paste.  However I don't really use it overal that much, pizza is the only time we use tomato paste.