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March 21, 2016

It’s Not Just About Weight–Body Composition Matters

Written by: Christina Dauer, MPH, RD, LDN, CDE

If I had a nickel for each time I heard someone say “muscle weighs more than fat”, I’d be off on a Caribbean cruise right now! Let’s bust some myths about the fat versus muscle debate and highlight the importance of improving and tracking body composition.

Myth # 1: Muscle weighs more than fat.

FALSE. Below is a model showing fat and muscle tissue. If you picked these up, they would each weigh five pounds.  Five pounds is five pounds, whether it is 5 pounds of muscle or fat. The difference is that muscle tissue is denser than fat tissue and thus it takes up less space in the body for the same pounds. This is one reason why clothes fit better and you lose inches as you lose body fat. You look leaner and thinner overall because muscle takes up less space in the body than fat tissue.

Myth #2: Muscle burns fat.

FALSE. Muscle can use both glucose, or sugar and fat for energy. What is true – is that muscle tissue is more metabolically active than fat tissue!  This means if you have a higher percentage muscle mass then you will have a higher metabolic rate and will be capable of burning more calories daily than someone with a lower muscle mass and higher percentage body fat, who is your same height, weight, age and gender. When you cut calories and start exercising to lose weight, you will start to burn body fat for energy.  In some cases, your body may also break down some muscle tissue for energy as well. The more muscle mass you lose, the lower your metabolic rate will be, meaning you will need to eat fewer calories to continue to produce weight loss. You can help preserve your muscle mass and metabolic rate by adding regular strength training as part of your exercise routine and by eating at a healthy calorie level for weight loss, and including adequate amounts of protein for the maintenance of muscle mass.

Myth #3: Fat turns into muscle (or more often heard, “my muscle has turned into fat”).

FALSE. Muscle and fat are two different tissue types and they cannot convert back and forth between each other. Fat is made up of adipose tissue, while muscle is made of proteins. It’s a common misconception that fat tissue is converted to muscle when you start exercising and changing eating habits.  In reality, you are simultaneously burning fat as fuel, especially through cardio workouts, while preserving or increasing your muscle mass through resistance training. One way to monitor these changes is to check body composition at regular intervals throughout the weight loss process.

What is “body composition”?

Body composition is a measure of what your body weight consists of—how much of it is fat, lean weight (muscle and bone) and water.

Why is tracking body composition important?

Tracking your body composition helps you maintain or build healthy proportions of muscle and fat. Keeping these ratios in a healthy range can produce significant health benefits such as reduced risk for chronic illnesses (i.e. cardiovascular disease and diabetes). Nothing is wrong with “weight watching”, but watching your weight is just a starting point. Monitoring body composition, as well as the weight on the scale, can ensure that you are decreasing your percentage of body fat and increasing your percentage of lean muscle tissue.  In addition, it will ensure that you are not losing valuable, metabolically active, muscle tissue through eating too few calories or losing weight too fast.

How do you track body composition?

Historically, health professionals have relied on the use of skinfold calipers to provide a measure of body fat. However, this method is highly prone to human error. Now, healthcare professionals use a more consistently accurate method called “bio-electrical impedance analysis (BIA)”. Fat and muscle tissue produce different levels of resistance to an electrical current flowing through them. BIA passes a safe electrical signal through the body, which measures the resistance levels as the signal travels. This provides an accurate estimate of the percent of weight that is fat versus lean tissue (muscle and bone) and water. Healthcare professionals such as registered dietitians often offer BIA testing as part of a weight management program.

Why is strength training so important for health and improving body composition?

Strength training is an important, but often disregarded part of a healthy physical activity regimen. Many think only of cardio workouts to help produce weight loss and manage chronic disease. For those with diabetes, studies have shown that regular strength training increases activity of GLUT 4 receptors in the muscle tissue.  These receptors help move glucose from the blood inside the cell, even without the help of insulin. So, people with diabetes who add strength training to their routine can improve their blood sugar management as a result. For those losing weight, strength training can help to preserve metabolically active muscle mass while they lose body fat. For everyone, strength training helps build muscle strength and stamina, which can make all of your workouts, including cardio workouts, more productive.  Many studies have shown that regular weight training exercise can help strengthen your bones and even may help build new bone. Strong bone density is important for prevention of osteoporosis and fall-related fractures.

So, how much strength training should you do?

Two to three strength training sessions a week lasting 20 to 30 minutes are sufficient for most people. This could include using free weights, weight machines, resistance bands or exercises that use your own body weight as the resistance such as lunges, squats or pushups. Be sure to check with your doctor first before starting any new exercise routine.


Am J Cardiol. 2016 Feb 2. pii: S0002-9149(16)30155-2. doi: 10.1016/j.amjcard.2016.01.033. Relation of Muscle Mass and Fat Mass to Cardiovascular Disease Mortality. Srikanthan P1Horwich TB2Tseng CH3.

Measuring and Evaluating Body Composition, American College of Sports Medicine

Wyatt Holly R, et al. Resting Energy expenditure in reduced-obese subjects in the National Weight Control Registry. Am J. Clin. Nutr June 1999 vol 69 no 6 1189-1193

Holten, Mads K. et al. Strength Training Increases Insulin Mediated Glucose uptake GLUT4 content, and insulin signaling in skeletal muscle in patients with Type 2 diabetes. Diabetes. February 2004 vol. 53, no 2 294-305.

Layne JE, Nelson ME. The effects of progressive resistance training on bone density: a review. Med Sci Sports Exerc. 1999 Jan;31(1):25-30.

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