Prevention magazine is the country's most authoritative, trustworthy, and innovative source for practical health, nutrition, and fitness information. Now, its editors bring you a weight-loss plan that's specifically designed to target your number-one trouble spot: BELLY FAT.     For women over 40, belly fat is incredibly stealth and incredibly stubborn. It's also the most deadly, contributing to a higher risk of heart disease, diabetes, and chronic illness than any other type of fat on your body. Finally, science has helped uncover a key dietary weapon in the fight against belly fat. Monounsaturated fatty acids, or MUFAs, help dieters lose more weight--in their bellies specifically--and keep it off longer.     Flat Belly Diet! will lead you step by step, day by day, meal by meal toward a flatter belly...and a longer, healthier life.