It’s all about the digestion. Our body digests roasted bread easier than fresh bread.
As we know, bread is a representative of starchy food. Most of the time it is made from refined wheat flour with a high starch content. When you toast or roast your bread, you break down the long chains of starch molecules to their smaller parts, dextrins. Dextrins give your roasted bread a nice brown colour and a characteristic taste. They are partially soluble in water, what makes roasted bread easier to digest compared to fresh bread with its long-chained insoluble starch molecules. And the easier your body can digest food, the more energy you have after your meal!