Gluten-free foods in a processed form may contain A LOT of calories. In addition to having more calories than non-gluten free items, most are still unrefined meaning that the grains are not enriched with iron, B vitamins, etc. And people who are eating gluten free for the right reasons (celiac, gluten intolerance) may need all the nutrients they can get to heal.
Better ways to eat gluten free are to stick to whole, natural foods. Like any fruit in its natural state, any vegetable in its natural state, nuts and seeds with or without salt (but check ingredients when smoked or in a processed trail mix item), and whole grains like quinoa, white or brown rice, amaranth, buckwheat, corn, millet, teff, etc. Protein sources like chicken, pork, beef, and seafood can be cooked from scratch so that you avoid gluten sources in marinades, rubs, etc.
Living without gluten does not have to mean living with bigger clothes!