Both fat and muscle contribute to your bodies total weight and both fat and muscle burn calories 24 hours per day. However, depending upon the authority you reference, muscle burns between 7-10 (average 6) calories per pound, every 24 hours and fat burns between 2-3 calories per pound every 24 hours.
Too much fat and not enough muscle?
The average male body has between 12-20% body fat mass and for females the range is 18-25%. It is estimated that average muscle mass for males is approximately 42% and for females is 36%. Males generally have a physiological advantage over females and can burn calories a lot faster than women simply due to the higher % of muscle mass. Ideally, during weigh loss you want to maintain muscle mass, whether you are a male or female.
However, if the muscle mass is reduced and out of proportion so is your bodies ability to burn calories. A loss of just 5% of body muscle mass in a 180 pound male … who started with a 42% muscle mass (approximately 76 pounds of muscle) … is approximately 3.8 pounds of muscle loss. This loss equates to a reduction of only 23 calories/day (3.8 X 6 calories per pound) being burned. However for someone trying to lose body fat, those additional 23 calories per day, over 1 year equates to approximately 2.3 pounds of body fat staying in place. If you are trying to lose weight, a reduction in fat not muscle should be the goal.
Outside of illness, one cause of muscle loss is rapid weight loss often seen in very low calorie “crash diets”. The Basal Metabolic Rate, (BMR) is the amount of calories the body needs at rest, … without performing any physical activity. The Mayo Clinic points out that your basal BMR accounts for about 60 to 75 percent of the calories you burn every day. A very lower caloric intake that is lower than the BMR, can result in a high percentage of muscle loss. Severe diets can result in a loss of 50% fat and 50% muscle weight. This impacts the BMR and can lower metabolism .
Another cause of muscle loss can be seen in individuals who are inactive. As we age we also lose muscle mass at an accelerated rate. This muscle loss combined with a lack of activity can result in a condition known as age-related sarcopenia or sarcopenia with aging. After age 30 the body loses approximately 3-5% of its muscle mass over the next decade, approx 8% is loss between age 40-50, 15% is loss each decade after 50 and 30% each decade after age 70. A loss of muscle mass equates to a lowering of metabolism.
What can be done to stop muscle loss?
Muscle loss during weight loss or from age-related sarcopenia can be mitigated by including strength exercises, regularly lifting weights or by including push-ups and other strength-oriented calisthenics, and by maintaining sufficient protein intake.
A minimum of 0.8 grams up to 1 gram of protein/ kg of body weight is commonly referenced in the literature and some sources recommend up to 1.2 grams of protein/ kg of body weight. But don’t wait until the dial on the scale tells you it’s time to lose weight or you develop a muscle mass deficiency.
According to Scottsdale, Arizona Registered Dietitian and Nutritionist Bonnie Roill, RDN CPT, CHC, The weight loss strategist™, a regular exercise routine that includes both cardiovascular and strength building exercises and a healthy balanced diet should be part of your daily healthy lifestyle routine. Consult a professional Registered Dietitian/Nutritionist for you nutrition needs and a professional Certified Personal Trainer for you exercise needs.
This information is not intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical/nutritional/fitness advice.
Sources: http://www.mayoclinic.com/health/metabolism/WT00006, http://www.cnn.com/2009/HEALTH/expert.q.a/06/05/building.muscle.nutrition.jampolis/, http://answers.webmd.com/search-results?ques=how%20many%20calories%20burned%20by%20muscle, Marieb, EN; Hoehn, Katja (2010). Human Anatomy & Physiology (8th ed.). San Francisco: Benjamin Cummings. p. 312. ISBN 978-0-8053-9569-3, http://en.wikipedia.org/wiki/Muscle, http://exercise.about.com/od/exerciseworkouts/f/muscle.htm, http://www.acefitness.org/fitnessqanda/fitnessqanda_display.aspx?itemid=358, Evaluation of specific metabolic rates of major organs and tissues: comparison between men and women, en.wikipedia.org/wiki/