SEIF 4
It is forbidden to eat before Kiddush. This comes from a Machlokes in the Gemara which asks that if someone eats before Kiddush, is he still allowed to make Kiddush or is he now prohibited from performing it. From here it appears that both sides agree that eating is forbidden, the Machlokos revolves around whether one who transgresses this prohibition is still allowed to say Kiddush or not. There is another Gemara which seems to imply that "Shabbos establishes itself" with a prohibition to eat before Kiddush.