The internal and external obliques, which I like to call "nature's girdle," are located at the sides of the rectus abdominis. They are the muscles you use when you bend sideways at the spine or twist at the waist. They also contract to compress the abdomen, so you should work them just as hard as you work the rectus abdominis. Adding a twist to crunches works, as well as dumbbell side bends, but be careful not to use any jerky motions, especially if you've had back problems.
There’s a reason everyone harps on about protein: Not only does it help keep you full, but it’s also responsible for repairing the tiny tears caused by strength training in your muscles. This helps them grow bigger and stronger, nudging out body fat in the process. As a general rule of thumb, aim to get at least 70 grams of protein throughout the day, says Dr. Cheskin.