For the first two meals (Friday night and Shabbos morning), one should definitely eat bread. This can be challah, bagels, matzah, etc.
However, the purpose of this mitzvah is to enhance one’s oneg shabbos, not to cause pain or discomfort. Therefore, if one doesn’t feel like eating, he doesn’t have to force the bread down his throat.
In that case, to have kiddush b’makom seuda, he should eat a kezayis of mezonos (cake, etc.) or at the very least, drink an additional revi’is of wine after making/ hearing Kiddush.
From Rabbi Eli Mansour’s Web site: