The starch and other carbohydrates in bread are converted to glucose, which, according to Davids book, is not addictive or metabolism destroying.
Cutting down on total carbohydrates does seem to be necessary for some people to lose weight though, and has been associated with lower risk of heart disease in some recent studies.
And the gluten (which is actually the protein component) in wheat is implicated in various digestive and autoimmune problems, which is why gluten free products etc are becoming more common.