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What Is Fat-Free Body Mass?

author image Janet Renee, MS, RD
Janet Renee is a clinical dietitian with a special interest in weight management, sports dietetics, medical nutrition therapy and diet trends. She earned her Master of Science in nutrition from the University of Chicago and has contributed to health and wellness magazines, including Prevention, Self, Shape and Cooking Light.
What Is Fat-Free Body Mass?
Physical activity plays a pivotal role in maintaining and building lean mass. Photo Credit Blend Images - JGI/Jamie Grill/Brand X Pictures/Getty Images

Fat-free mass, also known as lean body mass, refers to all of your body components except fat. It includes your body's water, bone, organs and muscle content. However, when it comes to weight management and body composition, fat-free mass refers primarily to muscle mass. Because most Americans are considered overweight or obese, increasing lean mass and reducing body fat plays a pivotal role in improving your health and well being.

Fat-Free Lean Body Mass and Weight Management

Your body consists of over 600 muscles, all serving as a vital reservoir for amino acids, which your tissue and organs require for survival. Muscle mass is dense and requires more energy to maintain than fat, making it a preferential component of your body composition, since muscle mass burns more calories than fat mass. Therefore, the higher your muscle mass, the higher your metabolism -- the amount of calories burned each day. Maintaining a healthy amount of lean mass contributes to weight management and helps to keep your body functioning well overall.

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Healthy Ratio of Lean Mass

The composition of your weight is just as important as how much you weigh, and a vital part of maintaining optimal health is having a balanced ratio of lean mass to fat. Be aware that some fat is essential to your health. The minimum amount of fat needed to remain healthy is around 3 percent for men and 12 percent for women, according to the American College of Sports Medicine. Non-essential fat is anything above this estimated amount and serves as extra fat stored primarily in your fat cells and the tissue directly beneath your skin, known as subcutaneous fat.

It's acceptable to have some non-essential fat, but too much can cause or contribute to health problems. A healthy body fat percentage ranges from 10 to 22 percent for men and 20 to 32 percent for women, according to ACSM. This means a healthy percentage of lean mass is 78 to 90 percent for men and 68 to 80 percent for women.

You'll get the most accurate assessment of your body fat levels if you consult a professional. They use underwater weighing, X-ray-based measuring or skin calipers to figure your body fat percentage and whether you're within a healthy range.

Maintain Lean Mass with Dietary Protein

It's important to get enough amino acids from protein sources in your diet, especially if you're following a reduced-calorie meal plan to lose weight. Without enough amino acids coming from food, your body is forced to break down muscle mass as a source of amino acids. This can cause you to lose a significant amount of muscle mass during weight loss, especially if you follow a starvation or fad diet to drop weight quickly. Getting enough protein helps maintain the lean mass you have and encourages your body to preferentially break down fat for energy, thus minimizing the amount of lean mass you lose and increasing the amount of fat burn.

The general protein intake recommendation is 0.8 grams per kilogram of body weight, which means an 180-pound person needs close to 65 grams of protein each day. However, this may vary depending on your situation. For example, if you're on a restricted-calorie diet, you need more protein to encourage your body to utilize fat instead of lean mass for energy. A study published in the British Journal of Nutrition in August 2012 found that bumping up to 1.2 grams of protein per kilogram of body weight is more beneficial when you're cutting calories to promote weight loss.

Make sure to get protein from lean sources like eggs, yogurt, tofu, chicken, turkey, nuts, seeds, fish and seafood, sirloin and other lean cuts of beef.

Physical Activity Builds and Maintains Lean Mass

In addition to dietary protein, physical activity plays a pivotal role in maintaining and building lean mass. When you don't get enough physical activity, the body is more likely to break down muscle for energy. The old saying that if "you don't use it, you lose it," rings true when it comes to muscle mass. In addition to helping control your weight, physical activity has a number of other health benefits such as helping to lower blood pressure, improving mood, and reducing the risk of chronic diseases such as diabetes and heart disease.

In general, a good health and fitness plan includes 150 to 250 minutes of moderate exercise each week, according to the American College of Sports Medicine. For optimal weight loss benefits, more than 250 minutes per week is necessary. If you're not used to exercising regularly, start slowly and build up gradually to help reduce the risk of injury and help your body adjust.

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