Back and armpit fat might cause bumps or bulges over a strapless dress or bikini strap, but they don't pose a significant health risk. Unlike deep-abdominal fat, which increases inflammation and ups your risk of disease, a small amount of fat in your back and armpit area won't put you on on track to cardiovascular disease. You can still get rid of it and minimize its appearance, however, with diet, exercise and styling tweaks.
Cut Calories to Lose Body Fat
First things first -- spot reduction is a myth. That means you can't decide to lose body fat from your back and armpit without affecting other areas of your body -- you'll lose fat all over, proportional to where it's stored. If your back and armpits are your "trouble areas" and carry excess fat even when you're thin, they'll likely be the last places to lose fat.
However, you can still minimize fat in this area by lowering your overall body fat percentage. Once you've figured out how many calories you need to maintain your weight -- a nutrition professional or online calculator can help you -- reduce your calorie intake by 500 to 1,000 calories each day. If you're already relatively thin, and will therefore lose fat more slowly than someone with more weight to lose, aim for a 500-calorie deficit, which will allow you to drop a pound a week.
Choose a calorie deficit that still allows you to get enough calories to avoid falling into a semi-starvation state. For women, that's 1,200 calories a day; for men, it's 1,800. Fill your diet with nutritious foods that provide fiber, protein, vitamins and minerals -- whole grains, nuts and seeds, beans, veggies, lean protein, fruit and low-fat dairy -- to meet your nutritional needs.
Toning Your Back, Armpits and Sides
Firm up your back and armpits with strength training. While most strength exercises won't help you actually burn fat, they will tone the underlying muscle so you look more fit, especially when you burn the overlying fat. Perform planks -- which strengthen your back muscles and abdominals -- as well as squats and deadlifts to tone your back muscles and improve your posture. And perform lat pulldowns -- or assisted pullups -- to tone your latissimus dorsi, the muscles that wrap around your back and into your armpit area. Working the back of your shoulders can also tone up your posterior shoulder-armpit-back area. Use rear flyes and inverted rows to tone your posterior shoulder muscles and back.
Accelerate Fat Loss with Cardio
Being active helps you torch more calories and melt away body fat faster than cutting calories through diet alone. For example, a 125-pound person will burn 420 working at moderate intensity for an hour on the stationary bike -- enough to burn 1,260 extra calories each week, one-third of a pound of fat, if you work out three times weekly.
Consider adding swimming, stationary rowing or boxing classes to your cardio routine. In addition to burning lots of calories for weight loss -- a 125-pound person would burn 600, 420 and 540 calories per hour, respectively -- these cardio exercises challenge your abdominals, arms and back, so you'll be toning these muscles as you burn calories.
Consider Your Clothing
In some cases, the appearance of an armpit or back fat bulge on women might not even come from excess body fat -- it might be caused by your clothing. An ill-fitting bra, in particular, can cause the appearance of back fat. If you're wearing too large a band, for example, it can ride up and create a bump that looks like back fat, bra stylist Madeline Lucas tells Divine Caroline. Too-small cups might also create the illusion of armpit fat. If your cups aren't large enough to contain all your breast tissue, it can bulge out at your armpits and create the illusion of extra fat. See a stylist for a professional fitting, so you can minimize armpit fat by wearing a bra that fits properly.