Breasts are made up mostly of adipose tissue, and the amount of fat you have on your body affects the size of your boobs. When you lose overall body fat, you lose weight in your breasts, reducing the size of your boobs. While spot training does not exist, you can enhance the appearance of a larger breast size while losing weight by training your pectoral muscles.
Increase the size of your pectoral muscles, the muscles underlying your breast tissue, with heavy weights and low-repetition strength training. The greater the weight, the better chance you have of building larger chest muscles. This is more beneficial to maintaining a greater chest size than lifting lighter weights with more reps. The latter promotes toning and weight loss.
Use classic push-ups to build your chest, shoulders and arm muscles. Lie face down with all of your weight shifted on your hands and toes. Slowly bend your arms and dip as low as you comfortably can, and then push-up to the starting position. If you are a beginner, do modified push-ups where your knees are bent, resting on the floor instead of straight. Aim for four sets of 20 reps, three days a week.
Pay attention to the type of foods you eat. This can have an effect on your weight loss efforts. You want a well-rounded diet that has plenty of protein and complex carbohydrates. If you cut down too much on carbs, this can encourage a greater fat and water loss, which may encourage loss of your boobs. For overall weight loss, avoid sweets, alcohol, sodas and other empty calories. Eat smaller, more frequent meals. These helps your metabolism stay revved through the day instead of two to three larger meals with a longer time frame between each.
Engage in cardio to get rid of fat. The type of cardio you choose may affect boob size. Activities, such as elliptical training, rowing and cross country skiing, work the upper and lower body while burning calories. These can help strengthen your pectoral muscles, making them appear larger. Aim for at least 30 to 45 minutes of cardio five days a week.