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.
2. Go to sleep earlier: A study in BMC Public Health found that people who racked up insufficient sleep on the reg were more likely to have a higher BMI. Meanwhile, researchers from the University of Chicago found that sleep loss causes decreased glucose tolerance and insulin sensitivity (those processes that cause your body to shuttle nutrients into fat cells instead of muscle cells) as well as elevated levels of ghrelin—the hunger hormone—and cortisol, the stress hormone that encourages your body to store fat. What’s more, the less you sleep, the less testosterone your body is able to produce. In short, skimping on sleep messes with all the hormones that help extra fat off your body—so hit the hay already. Shoot for at least 7 hours a night, more if you’re training hard because your body needs more time to repair and rest.
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.