The National Sleep Foundation, along with a multi-disciplinary expert panel, found that adults require seven to nine hours of sleep to properly rest and reset the body. Getting anything less than six and a half hours of sleep regularly will cause the body to release more of the stress hormone cortisol—which signals the body to store new fat cells. Less sleep also leads to increased appetite levels. And both of those results lead to weight gain, according to one University of Chicago study.

Stress is a fact of modern life, but we know it's pretty bad for your body. A Yale University study found the more your body secretes cortisol, the more likely you are to store fat in your midsection. Which means that you and your buddy could be eating the same and training the same, but if he's managing his stress and you're not, you'll put on weight while he won't. And that sucks. So make a little time each day for self-care, be it some relaxing reading, journaling or meditation.

For every meal and snack, you want a combination of complex carbohydrates with protein and fat. That means instead of a bag of chips from the vending machine, plan ahead with a combinations like greek yogurt with a banana, whole grain crackers with string cheese or an apple with a little peanut butter. The protein and fat not only provide quality fuel but they slow down digestion and keep your blood sugar from spiking. In the morning, instead of plain oatmeal made with water, make it with milk for added protein. Then stir in a tablespoon or two of nuts and fruit for healthy fats and fiber.

It's not about sit-ups. It's about training and toning your whole body because more muscle mass equals a faster firing metabolism—and that's what melts away the belly fat. The simple formula when it comes to fat loss is this: if you eat fewer calories than you burn, you'll lose weight. Let's do the math. A pound of fat equals 3,500 calories. Burning just 100 calories each day for 365 days is roughly 36,500 calories—equivalent to 10 pounds of pure fat lost in a year. You could double your weight loss to 20 pounds by burning 100 calories each day and trimming an additional 100 calories from your diet.

Those satisfying but otherwise empty carbohydrates and starches like white breads, pasta and potatoes? They digest quickly, causing an uptick in blood sugar and insulin levels. Since insulin is a storage hormone, it likes to store excess blood sugar as fat—visceral belly fat specifically. So cutting these refined carbohydrates should be the cornerstone of your nutrition plan when you're looking to lean up. A Harvard study of more than 60,000 dieters found that those who cut back on bread, pasta and starches lost more weight than those who simply cut back on fat and calories.

This is the hardest to do, of course, especially in this world of ready-made meals, sugar-packed drinks and seemingly healthy foods such as fruits and protein bars which can have a surprisingly high amount of sugar. Those high-sugar foods, not surprisingly, spike your blood sugar which causes a flood of insulin. And, as we said, more insulin leads to packing on belly fat.