To lose belly fat you need to lose overall body fat, since spot reduction is not possible, notes the American Council on Exercise. This can be challenging when you are trying to gain muscle mass weight at the same time. To effectively gain muscle mass and lose weight you need to eat a diet with little to no processed, refined, sugary or saturated fats, says author Tosca Reno, "The Eat Clean Diet." Also, choosing higher calorie, nutrient-dense foods will help refuel your muscles for growth without fat weight gain, according to acefitness.org.
Eat five to six meals a day to increase your metabolism and keep your energy high. Space your meals out every two to three hours. Eat a higher carbohydrate meal two hours before your weight lifting session and a higher protein meal one hour after.
Eat monounsaturated fatty acids, MUFA's, daily to lose belly fat, according to the March 2007, "Journal of Diabetes Care." Add one serving of a MUFA such as 1/4 cup avocado, 10 nuts, 1/2 cup seeds, 1/4 cup 65 percent dark chocolate with no added sugars, 10 olives or 1 tbsp. of olive or flaxseed oil to every meal.
Eat lean proteins with every meal to help refuel your muscles for growth. Choose proteins such as egg-whites, lean beef, chicken, fish, turkey over higher fat proteins. Eat 1.4 to 1.8 grams per kilogram of body weight daily to increase muscle mass, notes Eat Right.
Choose only complex carbohydrates such as brown and wild rice, whole grain cereal, pasta and bread, steel-cut oatmeal and fresh fruits and vegetables. Avoid high calorie, low nutrient carbs such as pastries, cookies, candy, pies, bagels, white bread, rice and pasta. Eat a balance of complex carbs throughout the day with the highest percentage at your first meal of the day to drop body fat, according to the June 2008, "Science Daily."
Drink water throughout the day to stay properly hydrated, 13 cups for men and 9 cups for women, recommends mayoclinic.com. Avoid juices, sodas, diet sodas, caffeinated drinks and alcoholic drinks which are high in calories and sodium and can cause water retention, according to acefitness.org.