Body composition interpretation: Contributions of the fat-free mass index and the body fat mass index

doi:10.1016/S0899-9007(03)00061-3

Nutrition

Volume 19, Issues 7–8, July–August 2003, Pages 597-604

https://doi.org/10.1016/S0899-9007(03)00061-3 Get rights and content

Abstract

Objective

Low and high body mass index (BMI) values have been shown to increase health risks and mortality and result in variations in fat-free mass (FFM) and body fat mass (BF). Currently, there are no published ranges for a fat-free mass index (FFMI; kg/m²), a body fat mass index (BFMI; kg/m²), and percentage of body fat (%BF). The purpose of this population study was to determine predicted FFMI and BFMI values in subjects with low, normal, overweight, and obese BMI.

Methods

FFM and BF were determined in 2986 healthy white men and 2649 white women, age 15 to 98 y, by a previously validated 50-kHz bioelectrical impedance analysis equation. FFMI, BFMI, and %BF were calculated.

Results

FFMI values were 16.7 to 19.8 kg/m² for men and 14.6 to 16.8 kg/m² for women within the normal BMI ranges. BFMI values were 1.8 to 5.2 kg/m² for men and 3.9 to 8.2 kg/m² for women within the normal BMI ranges. BFMI values were 8.3 and 11.8 kg/m² in men and women, respectively, for obese BMI (>30 kg/m²). Normal ranges for %BF were 13.4 to 21.7 and 24.6 to 33.2 for men and women, respectively.

Conclusion

BMI alone cannot provide information about the respective contribution of FFM or fat mass to body weight. This study presents FFMI and BFMI values that correspond to low, normal, overweight, and obese BMIs. FFMI and BFMI provide information about body compartments, regardless of height.

Introduction

Malnutrition and obesity have been shown to increase morbidity and mortality.1, 2 Epidemiologic studies have also shown that low and high body mass index (BMI) values increase morbidity and mortality.3, 4 Research also has indicated that body composition, more than BMI, is a primary determinant of health5 and a better predictor of mortality risk than BMI.6

Over half of the adults in the United States7 are overweight, and an increasing number of Europeans are becoming overweight. Obesity is normally defined by BMI. BMI values between 18.5 and 24.9 kg/m² are considered normal; individuals with BMI values from 25 to 29.9 kg/m² are considered overweight and those with values greater than 30 kg/m² are considered obese.8 Underweight subjects (BMI < 18.5) are also at nutritional risk.9 Thus, prevention of weight gain and low body mass are a public health priority.

Recent studies also have shown that weight and BMI alone are not adequate measurements of underlying changes in fat-free mass (FFM) and body fat mass (BF) during menopause,10 aging,11 and illness in general.12, 13

Little is known about what constitutes “normal” FFM and BF. “Healthy” body fat percentages (%BF) have been suggested to be in the ranges of 12 to 20 for men and 20 to 30 for women.14 Even though individuals with %BF above these cutoff values have an increased likelihood of being functionally obese, not everyone will be. Higher %BF values have been reported in apparently healthy populations.15, 16 We also found that hospitalized patients are more likely to have low FFM and low or excess BF,12, 17 suggesting increased health risks in patients.

Until now, it has been customary to use absolute FFM (kg) and %BF to evaluate nutrition status.18 Because FFM and BF change with height, weight, and age, it is difficult to determine whether individual subjects have low or high FFM or BF. The use of FFM in absolute terms complicates interpretation because FFM is closely related to height and decreases with age. The use of percentage of FFM does not adequately reflect nutrition status because FFM automatically decreases in proportion to %BF increases. The colinearity between the two parameters limits the interpretation of absolute FFM and relative changes of FFM. Variations of FFM and BF with age and height also make it difficult to establish desirable ranges.

Just as BMI is useful in evaluating the excess or deficit in body weight of individuals of different heights, the fat-free mass index (FFMI; kg/m²) and body fat mass index (BFMI; kg/m²) are potentially useful in evaluating body composition parameters by effectively eliminating differences in FFM and BF associated with height.19 Height-independent body composition parameters (FFMI and BFMI) allow height-independent interpretation of nutrition status, comparisons of results between studies, and the development of body composition percentile tables.

The use of FFMI and BFMI allows the tracking of the effects of illness, treatment, or aging in individuals and in groups because they can be interpreted as absolute values or by classifying individuals or groups of individuals as normal or abnormal (low and high). FFMI also permits one to determine whether lower FFM with age is due to shorter height in older subjects or to changes in body composition. FFMI and BFMI also identify individuals with excess muscle mass but without excess BF. These changes are of interest at the group or population level.

The purpose of this population study was to determine FFMI, BFMI, and %BF ranges in subjects with low, normal, overweight, and obese BMI. Our study presents FFMI and BFMI in 5629 healthy men and women across the age span, from 15 to 98 y. The ranges of FFMI and BFMI for a given BMI category can be used to evaluate whether FFM is low and BF is low or high in adults.

Section snippets

Subjects

Healthy adults (2982 men and 2647 women), age 18 to 98 y, were non-randomly recruited through advertisements in local newspapers with an offer of free bioelectrical impedance analyses (BIAs), at exhibitions at trade fairs and fun runs, among public administration staffs, and by invitations sent to leisure clubs for the elderly. The anthropometric and BIA data and the number of healthy subjects are shown in Table I. All subjects were ambulatory whites (Western European) without known pathologies

Results

Table I shows the anthropometric and body composition measurements of healthy men and women between 18 and 98 y. Height was highest in the youngest men and women and progressively decreased thereafter. Weight was progressively greater in older than in younger subjects. BMI (Table I) was progressively greater in older than in younger men and women.

Discussion

BMI does not separate body compartments into FFM and BF. Because research has indicated that body composition is a primary determinant of health,5 FFM and BF compartments should be determined as part of a health assessment. FFM and BF change with height, weight, and age. It is therefore difficult to determine whether individual subjects have low or high FFM or BF. FFMI and BFMI eliminate differences in FFM and BF due to height and offer the advantage of having one set of recommended ranges,

Conclusion

BMI alone cannot provide information about the respective contributions of FFM and FM to body weight. This study presented the FFMI, BFMI, and %BF values that correspond to low, normal, overweight, and obese BMIs. FFMI and BFMI can provide meaningful information about body compartments, regardless of height.

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^☆: We thank the Foundation Nutrition 2000Plus for its financial support.

View full text

Applied nutritional investigationBody composition interpretation: Contributions of the fat-free mass index and the body fat mass index☆

Abstract

Objective

Methods

Results

Conclusion

Introduction

Section snippets

Subjects

Results

Discussion

Conclusion

Am J Surg

Am J Clin Nutr

Am J Clin Nutr

Am J Clin Nutr

Nutrition

Am J Clin Nutr

Nutrition

Am J Clin Nutr

Nutrition

Am J Clin Nutr

Am J Clin Nutr

Respir Med

Clin Nutr

Am J Clin Nutr

Am J Clin Nutr

Am J Clin Nutr

Body mass index and all-cause mortality among people age 70 and overthe Longitudinal Study of Aging

Int J Obes

Mortality associated with body fat, fat-free mass and body mass index among 60-year-old Swedish men-a 22-year follow-up. The study of men born in 1913

Int J Obes Rel Metab Disord

Body composition, not body weight, is related to cardiovascular disease risk factors and sex hormone levels in men

J Clin Invest

Applied nutritional investigation
Body composition interpretation: Contributions of the fat-free mass index and the body fat mass index☆