Here are three secrets to getting a flat belly: reducing inflammation, lowering body fat percentages and building a strong core.
1. Reduce Inflammation
Try limiting gluten and dairy (dairy without probiotics - should still eat kefir and Greek yogurt for calcium and reducing inflammation, as well as increasing your antioxidant intake). This will surely help reduce inflammation in the body. Antioxidants come from plants and vegetables and are best in whole form. However, supplementing your diet with multi-vitamins or specific antioxidants can help.
Your lower belly houses your large intestines. When you eat foods that are harder for your body to digest (which means they are usually low in antioxidants) or have high intake of sodium or other toxins (alcohol, pharmaceutical drugs, etc) and low intake of fiber, your intestines swell to try to absorb more of the nutrients. Think of this as, it's hard to absorb nutrients that are not there and if they pass through too quickly.
* Make sure you are eating at least 25 grams of fiber a day coming from fruits or vegetables. Aim for 35 grams of total fiber per day. These additional 10 grams of fiber can come from whole grain foods. If you must eat bread, aim for at least 4 grams of fiber per serving and under 110 calories per slice.
2. Lower Body Fat and Increase Lean Muscle
The only way to lower body fat is to burn more calories and build muscle. Cardio, strength training and conscious calorie intake is necessary. Depending on your current body fat the combination of these is something that is specific to each individual. In general the 3500 calorie deficit per pound should come from a combination of both calorie restriction and exercise unless the current calorie intake is lower than 1200 calories a day. Building muscle means putting overload or fatigue in a general movement pattern. Passive movements like walking do not increase lean muscle mass. Plyometrics, running to some degree and weight training will contribute to increased lean muscle.
3. Build a Strong Core
The core comprises of the obliques, rectus abdominus, and transverse abdominals group. Crunches will not give you a flat belly. They help build a component of a strong core but should not be your only ab exercise. You'll need to incorporate rotational, lateral and diagonal patterns of core work to provide full support to holding your rib cage to hips together with a smooth overall appearance.
Try exercises that perform these types of movements.