Definition of Lean Body

The definition of a lean body is often subjective and judged by the beholder. However, there are concrete numerical ranges for body composition, or fat-to-lean mass, that are optimal for health. Guidelines for what constitute optimal lean body mass are based on relative levels of fat, and as such will differ between groups of people such as men and women. They also differ based on age and health status.

General Recommendations

According to guidelines from the National Institutes of Health, women should have a body fat of 20 to 21 percent, meaning that the rest of their body composition will be lean tissue — organs, muscle, bone — and water. A woman with more than 30 percent body fat is considered obese. The recommended body fat for men is 13 to 16 percent, with 25 percent or higher classified as obese.

Measuring Lean Tissue

Muscle Mass & BMI

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Lean tissue can be measured with a variety of devices, which range in technique, accuracy, cost and ease of use. Scales that use bioelectric impedence analysis (BIA), a small electric current that measures fat and lean tissue, can be purchased for home use. Calipers can also be purchased, but should be used by a trained professional. Advanced techniques which are more accurate and costly include underwater weighing and dual energy X-ray absorptiometry (DEXA), a scan that can measure muscle, fat and bone density.

Benefits of a Lean Body

Having enough lean body mass to fall under the recommended fat levels reduces the risks for health problems such as high blood pressure, high cholesterol and diabetes, according to the American Heart Association. The Centers for Disease Control recommend changes to diet and increased exercise as a means to increase lean body mass.

Lean Body Misconceptions

What Is Normal Body Fat?

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The definition of a lean body is not necessarily a body devoid of fat. Certain groups of people, such as athletes and trained bodybuilders, will have very low body-fat levels and high lean-tissue mass, but this is not ideal for everyone. Some fat is essential for vital bodily functions such as energy storage and organ insulation, and most Americans fall at or above the recommended fat ranges.