With the New Year upon us, millions of people are thinking hard about their New Year’s resolutions, many of which will likely include ambitious nutrition and fitness goals. Given the increasing ease of measuring body composition and the known benefits of decreasing body fat percentage, it is no surprise that fitness professionals and consumers alike want to know how much body fat they should expect to lose.  Unlike the well-researched and accepted guideline that an individual should lose no more than 1-2 pounds per week, body fat percentage loss is not as well studied and no official guidelines have been published.  Still, most experts agree that a 1% loss per month is generally safe and doable.  However, it is important to recognize that most methods of measuring body fat (such as calipers, bioelectrical impedance analysis, etc) are prone to measurement error and detection of small changes in body fat percentage is just as likely due to this error as it is an actual change in body fat.Thus, it’s best to wait a couple of months to recheck body composition to see if you’ve made progress. Be sure to check out our body fat calculator.

How can I decrease my body fat?

Weight loss alone won’t necessarily lead to huge decreases in body fat since weight loss without exercise will lead to decreases in lean mass as well.  If you really want to decrease your body fat percentage you’ve got to eat better, do cardiovascular exercise AND remember to do resistance training to build up your lean mass, otherwise about 25% of every pound you lose will come from lean, calorie-burning muscle.  Assuming you do resistance training and all the weight you lose comes from fat, you can use the following handy formula to help you estimate approximately how much weight you’ll need to lose in order to achieve your ideal body fat percentage-

 **CAUTION: If you hate algebra, please disregard this formula and skip to next paragraph.

Desired body weight = Lean body weight/(1-desired body fat percentage)

Desired body weight = how much you will weigh when you achieve your desired body fat percentage.

Lean body weight = how many pounds of rock-hard, lean tissue you have right now (to know this you have to get your body composition measured.  Basically, what is not fat is lean).

Desired body fat percentage = your goal body fat percentage (in decimal form).

For example, Angela weighs 120lbs and has 25% body fat (30lbs fat, 90lbs lean).  Her goal is to have 20% body fat.  How much weight will she need to lose (assuming all of the weight loss comes from fat)?

Desired body weight = 90/(1-.20) = 113lbs

So she would need to lose 7lbs to achieve her goal (120-113=7).

What is my ideal body fat percentage?

Remember that ideal body fat percentage is different for men compared to women, as women require a higher body fat percentage in order to maintain menstruation and the ability to have children (see chart).  If you are curious to know what your body fat percentage is, check out the ACE website to find a fitness professional near you who can measure your body fat percentage, assess your official fitness, and get you on your way to a healthier, more fit you in 2010.

Natalie Digate Muth, MD, MPH, RD, is a registered dietitian and recent graduate of the UNC School of Medicine. She is an ACE-certified Personal Trainer and Group Fitness Instructor, and holds additional certifications with the American College of Sports Medicine and the National Strength and Conditioning Association. She has made several appearances as a nutrition expert on CW's San Diego 6, been quoted as a fitness expert in the New York Times and other newspapers and is an ACE Master Trainer and award-winning author. She is currently a pediatrics intern at UCLA Mattel Children’s Hospital.