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Body Composition Provides Predictive Mortality Risk


Relation of Body Fat Mass and Fat-Free Mass to Total Mortality – 7 Studies

The American Journal of Clinical Nutrition

Published: 12 January 2021




Fat mass and fat-free mass may play independent roles in mortality risk but available studies on body composition have yielded inconsistent results.


The aim was to determine the relations of body fat mass and fat-free mass to risk of mortality.


In pooled data from 7 prospective cohorts encompassing 16,155 individuals aged 20 to 93 y (median, 44 y), we used Cox regression and restricted cubic splines to estimate HRs and 95% CIs for the relation of body composition, measured by bioelectrical impedance analysis, to total mortality. We adjusted for age, study, sex, ethnicity, history of diabetes mellitus, education, smoking, physical activity, and alcohol consumption.Results

During a median follow-up period of 14 y (range, 3–21 y), 1347 deaths were identified. After mutual adjustment for fat mass and fat-free mass, fat mass showed a J-shaped association with mortality (overall P value < 0.001; P for nonlinearity = 0.003). Using a fat mass index of 7.3 kg/m2 as the reference, a high fat mass index of 13.0 kg/m2 was associated with an HR of 1.56 (95% CI: 1.30, 1.87). In contrast, fat-free mass showed an inverse association with mortality (overall P value < 0.001; P for nonlinearity = 0.001). Compared with a low fat-free mass index of 16.1 kg/m2, a high fat-free mass of 21.9 kg/m2 was associated with an HR of 0.70 (95% CI: 0.56, 0.87).Conclusions


Fat mass and fat-free mass show opposing associations with mortality. Excess fat mass is related to increased mortality risk, whereas fat-free mass protects against risk of mortality. These findings suggest that body composition provides important prognostic information on an individual’s mortality risk not provided by traditional proxies of adiposity such as BMI.

The American Journal of Clinical Nutrition

Published: 12 January 2021


Body composition is the proportion of fat and non-fat mass in your body. A healthy body composition is one that includes a lower percentage of body fat and a higher percentage of non-fat mass, which includes muscle, bones, and organs.

Knowing your body composition can help you assess your health and fitness level. Often, you will measure your body composition at the start of a weight-loss or fitness program and then check it periodically to monitor your progress.

What Is Body Composition?

Your body is composed of two types of mass, body fat, and non-fat mass.1 Here’s some key difference between the two:

  • Body fat: This can be found in muscle tissue, under the skin (subcutaneous fat), or around organs (visceral fat). Some fat is necessary for overall health. “Essential fat” helps protect internal organs, stores fuel for energy, and regulates important body hormones. But you may also have excess storage of fat and non-essential body fat.
  • Non-fat mass: This includes bone, water, muscle, organs, and tissues. It may also be called lean tissue. Non-fat mass tissues are metabolically active, meaning they burn calories for energy, while body fat does not.

Body fat percentage is a measurement of body composition telling how much of the weight of your body is fat. The percentage of your body that is not fat is fat-free mass. There are normal ranges for body fat, which differ for men and women.

Weighing yourself on a regular bathroom scale does not assess your body composition. A regular scale cannot tell how much of your total weight is comprised of water, fat, or muscle. To know whether your body composition is healthy, you should get an estimate of your body fat percentage. You can do so by taking simple measurements and entering them into a body fat percentage calculator.

Healthy Body Composition

The American Council on Exercise (ACE) gives the following ranges of values for different populations.

ACE Body Fat Percent Norms for Men and Women
Description Women Men
Essential Fat 10% to 13% 2% to 5%
Athletes 14% to 20% 6% to 13%
Fitness 21% to 24% 14% to 17%
Acceptable 25% to 31% 18% to 24%
Obese Over 32% Over 25%

Athletes tend to have lower body fat, which may be beneficial for performance in sports such as running and cycling. But having an extremely low body fat percent is a health problem. For example, the female athlete triad increases the risk of injury and health issues. It includes eating disordersamenorrhea, and decreased bone mass with an increased risk of stress fractures and osteoporosis.

If you are overweight or obese, you have an excessive amount of body fat and a high body fat percentage.

If your body fat percentage is too high, you can improve your body composition by gaining lean body mass through building muscle and bones and by losing excess body fat.

How to Measure Body Composition

There are several ways to get an estimate of your body fat percentage at home, at the gym, or from your doctor.

Bioelectrical Impedance

Bioelectrical impedance can be measured by handheld units and by BIA body fat scales that you step onto like a regular scale. These tools pass a small electrical current through your body.1 Fat, water, and lean tissue impede the current differently to give the reading.

Many scales are sold for home use and no special training is required. Some scales, like the Fitbit Aria 2, even sync with your fitness tracker so that you can see how changes to your daily activity and diet affect your weight.

Skinfold Measurements

Taking skinfold measurements is a method often used by fitness trainers or as part of a weight loss program. Calipers take measurements at different parts of your body and then a calculation helps translate them into a body fat percentage.


A DEXA scan, or dual-energy x-ray absorptiometry scan, is performed in a medical setting and can also be used to check for bone density.1

Hydrostatic Weighing

Hydrostatic weighing is a method that requires you to be fully submerged in water. This gold standard for body fat measurement involves being dunked in a water tank. It’s harder to find a clinic or gym that offers this service.

Factors Affecting Body Composition

Your body composition can also be influenced by factors you can’t control:

  • Age: People lose muscle mass as they age2 if they don’t maintain it with sufficient weight training. This results in a slower metabolism.
  • Genes: These play a role in whether you are naturally lean or have a tendency to retain fat, including where you store it.
  • Hormones: These can influence water retention and body composition.
  • Sex: Women have more body fat than men as nature’s way of preparing for pregnancy and nursing.

Should You Change Your Body Composition?

If your body fat percentage is too high, you may want to try to decrease it to improve your health, athletic performance, and well-being. You may also be able to lower your risk of disease. If your body fat percent is below the level of essential fat, you may also want to make changes to bring it, as that will reduce your health risks as well.

To change your body composition for better health and fitness, aim to increase muscle mass and decrease excess fat mass. You can change your diet, start an exercise program.

To learn more, contact us today at RenewFX Health