The answer to how fast you can lose pectoral fat is the rate at which you can lose fat in general. You can't lose fat from one area of the body. Being a man may be an advantage, however. Higher testosterone levels make muscle building and fat loss a little easier for men than women.
The Pound-a-Week Plan
It takes a deficit of 3,500 calories to burn 1 pound of fat. The generally accepted rate for safe weight loss is 1 to 2 pounds per week. It appears that your upper body may give up fat faster than your belly, meaning the benefits of a nutritionally balanced diet that includes all the major food groups and cuts back on empty calories from fats and sugars, combined with calorie-burning cardio, such as jogging or working on cardio machines, may show in your pectoral area first.
Change the Balance
While you can't convert fat into muscle, lean tissue is more dense than fat and takes up less room. Building pec muscles with pushups, flyes and bench presses while shrinking fat cells through diet and cardio will make your pec area leaner and improve your overall fat-to-lean tissue ratio.
According to Medical News Today, gynecomastia, or "man boobs," is also characterized by enlarged areola and tenderness. This condition is affected by hormones and probably will not respond to diet and exercise. See your physician to rule out more serious conditions or if you find it embarrassing.