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Healthy Weight Center

Why Am I Losing Body Fat But Not Weight?

03/12/2009

Question:

Is it possible to have lost 10% of your body fat without having lost 10% of your weight?

Answer:

When you lose weight, you are losing some body fat and some lean body mass (muscle mass).  The goal of a healthy weight loss regimen is to lose body fat, while preserving lean body mass.  Lean body mass is more metabolically active (i.e., burns more calories), so it's advantageous to retain as much as possible while you lose weight.  Someone with more lean body mass can consume more calories and maintain their weight than someone with the same body weight, but less lean mass.

The type of diet, degree of caloric restriction, type of exercise, and rate of weight loss can influence the proportion of weight lost as lean body mass.  The best way to achieve a healthy body composition and weight may be to moderately restrict calories, while including lean protein foods, such as poultry, fish, low-fat dairy products, beans, and legumes in your diet.  You want to avoid extreme calorie restriction and quick weight loss, since you will be more likely to lose lean body mass in this situation.  

Don't forget to include exercise in your weight loss regimen.  Strength training with weight lifting or resistance exercises is important to retain or even build muscle mass while you are losing weight.  You should combine this type of exercise with aerobic exercise, which helps to burn calories and lose body fat. 

To answer your question, you could lose body fat without losing much weight if you were gaining lean body mass at the same time.  Remember though that body fat measurements vary depending on the method used.  The most accurate techniques for measuring body fat are the hydrostatic method (underwater weighing) and dual energy x-ray absorptiometry (DXA scans).  Since both methods involve very expensive equipment and trained personnel, they are not accessible to most persons.  In reality it is not necessary to measure the percentage of body fat lost.  The important outcome of a healthy diet and exercise regimen is achieving a weight that is associated with overall health (increased energy, recommended blood pressure, normal blood lipid and glucose levels, etc.).  If you adopt healthy diet and exercise habits, you are likely to lose body fat, retain muscle mass, and achieve a healthy weight.

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Response by:

Bonnie J Brehm, PhD, RD Bonnie J Brehm, PhD, RD
Professor of Nursing
College of Nursing
University of Cincinnati