Get a flat belly by drinking smoothies. Most smoothie recipes are quick and simple to prepare, so they are ideal for an on-the-go breakfast or an after-work snack. Be sure to add foods that contain mono-unsaturated fatty acids to the smoothie to help belly fat melt off. Foods that contain mono-unsaturated fatty acids include avocados, flax seeds, and nut butters. Make a quick flat belly smoothie by blending together one cup of low-fat milk, a tablespoon of cocoa powder, two tablespoons of peanut butter and a sliced banana. Another option is to make a smoothie with a cup of frozen berries, one mashed avocado, and one cup mango juice.