While scaling back on specific macronutrients, like carbs or fat, may be key to successful weight loss, eliminating them completely won't do you any favors. The body needs some carbohydrates for energy, and small amounts of healthy fat to aid the absorption of disease-fighting antioxidants. If you're going the gluten-free, dairy-free, or vegetarian/vegan route, you've got to make up for the nutrients found in foods like whole-grain bread, low-fat milk or lean protein elsewhere in your diet. The smartest thing you can attempt to avoid altogether; sugar, says Mangieri.