The Facts With Decreasing "% of Body Fat"

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-

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).

(By Natalie Digate Muth )
Natalie Digate Muth, MD, MPH, RD