Applied nutritional investigationFat-free and fat mass percentiles in 5225 healthy subjects aged 15 to 98 years☆
Introduction
Significant changes in body composition occur with aging and are believed to be a consequence of imbalances between energy intake and energy needs associated with an increasingly sedentary lifestyle. Progressive increases in fat mass (FM) and progressive reductions in fat-free mass (FFM) have been noted. In adults, over- and undernutrition contribute to increased mortality and morbidity. In the elderly, the age-related loss of muscle mass, or sarcopenia, is prevalent and strongly associated with impaired mobility, increased morbidity and mortality, and lower quality of life.1
Much of our current understanding of the changes in body composition with advancing age comes from studies that are 30 y old.2 National surveys for reference data for body composition measures that have large samples and are suitable for describing differences between individuals and between levels of muscle and FM are needed. Because weight and body mass index (BMI) alone are not an adequate guide of underlying changes in FFM and FM during menopause3 and aging in general,4 body composition should be measured in clinical management programs and epidemiological and clinical studies of aging.4 Simple measurements for evaluating body composition such as skinfold measurements are easy to perform but not accurate or reproducible.5 Other methods require subject cooperation (underwater weighing) or sophisticated equipment and skilled technicians (tracer dilution, dual-energy x-ray absorptiometry [DXA], and neutron activation analysis).
More recently, bioelectrical impedance analysis (BIA) has been shown to be more accurate for determining leanness or fatness in humans.6 BIA provides a more reliable measurement of body composition with respect to FFM and FM than does BMI5 or simpler methods such as skinfolds and height and weight.7, 8
Two previous studies have reported percentiles for FFM, FM, and percentage of FM (%FM). Heitmann9 reported BIA-determined 10th and 90th percentiles for FFM, FM, and %FM in a large Danish adult population aged 35 to 65 y. Pichard et al.10 published BIA-determined percentiles for the same parameters in adults aged 18 to 65 y using different BIA equations for men and women and for obese and non-obese subjects. Although FFM and FM values for adults younger than 64 y are available, no data are available in older subjects, primarily due to a lack of appropriate BIA formulas applicable in elderly subjects and fewer healthy subjects being available. The recent validation of a single BIA equation in subjects 15 to 94 y with BMIs between 17 and 33.8 kg/m2 now permits the evaluation of FFM and FM in subjects older than 65 y.11
The aims of this study were to determine reference values for FFM, FM, and %FM by BIA in a large white (Western European) population of healthy subjects in Switzerland, including elderly subjects, observe their differences in age groups of 10 y in those 15 to 98 y, and develop percentile distributions for those parameters. The percentile data presented serve as reference to evaluate deviations from normal values of FFM and FM in healthy adult men and women at a given age.
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Subjects
Healthy adults (2735 men and 2490 women), aged 15 to 94 y, were recruited non-randomly through advertisements in local newspapers, by offering free BIA on an exhibition stand at trade fairs and fun runs, among public administration staff, and by invitations sent to members of leisure clubs for the elderly to participate in the study. The anthropometric data and number of healthy subjects per age group are shown in Table I. All subjects were ambulatory whites (Western European) who had no known
Results
Table I shows the anthropometric and bioimpedance characteristics of the men and women with no known pathologies. Age- and sex-specific percentile distributions for FFM, FM, and %FM of white adults are presented in TABLE II, TABLE III, TABLE IV and FIG. 1, FIG. 2, FIG. 3.
Discussion
Few studies have reported FFM and %FM in large population samples.5, 19, 20 In general, FM is derived by indirect methods. The development and validation of BIA now permit the determination of FFM and FM more accurately by an easy, portable, and inexpensive method.5, 8 Two previous studies have reported percentiles for FFM, FM, and %FM by BIA in subjects 15 to 65 y old9, 10 but did not evaluate men and women older than 65 y.
The aims of this study were to determine reference values for FFM, FM,
Application of BIA formulas in subjects with different ages and BMIs
The validity of BIA-determined FFM and FM directly depends on the equation used to translate the BIA-determined resistance and reactance values into FFM, FM, or total body water.5, 21, 22 FFM in the present study was estimated with a multiple regression equation that was previously validated against DXA in 343 healthy subjects 18 to 94 y old.11 Validation of the Geneva BIA equation was deemed necessary because published equations were inadequate for overweight, obese, and elderly subjects.
Comparison of BMI with previous studies
The BMIs in the present study can be compared with those in other epidemiologic studies. Median BMIs of 24.6 to 25.1 kg/m2 in 35- to 74-y-old men and 21.8 to 23.6 kg/m2 in 35- to 74-y-old women reported in a randomly sampled Swiss population23 were similar to those in the current study. In other studies, mean BMIs were 24.6 ± 3.6 kg/m2 in men and 25.3 kg/m2 in women aged 15 to 99 y in Finland,24 and median BMIs were 24.5 to 25.3 kg/m2 in men and 22.3 to 24.0 kg/m2 in women 35 to 65 y old in
Fat-free mass
In our study, the FFM peaked in men 35 to 44 y old and women 45 to 54 y old and declined thereafter, compared with declines beginning at age 60 y in men and 45 y in women in the study by Bartlett at al.27 Heitmann9 found that FFMs were highest in 35-y-old men and women and decreased thereafter.
Forbes28 suggested that a weight gain of 2.3 kg/decade is necessary to avoid losing FFM during aging. The low body weight increases reported in our subjects (approximately +5 kg in 40 y) would have been
Comparisons of percentiles with previous studies
The P50s for FM were 2.9 kg higher in men and 2.0 kg higher in women than in our previous study.10 The discrepancy stems from an underestimation of FM by the BIA equations used in the previous study. Recent validation of a single BIA equation against newer versions of DXA hardware and software allows more accurate predictions of FM and FFM and can be used to follow people longitudinally during aging and when significant BMI changes occur.
Although the median BMIs reported by Heitman9 in a Danish
“Ideal” fat mass
A recent round-table discussion36 suggested that the “best” FM percentages in terms of lowest morbidity and mortality averaged 12% to 20% in men and 20% to 30% in women. Forty-five percent of all men and 38% of all women in our study were above those recommendations (Table V). “High” FMs, defined as the P85, in this study were 25.6% in men and 35.7% in women, and “excess” FMs, defined as the P95, were 29.2% in men and 40.5% in women. Further research is necessary to determine to what extent
Study limitations
The subjects in this study were not randomly selected. However, the BMIs in our study were similar to the median BMIs of 24.6 to 25.1 kg/m2 in 35- to 74-y-old men and 21.8 to 23.6 kg/m2 in 35- to 74-y-old women in a randomly sampled population in Geneva.23
Subjects with extreme body FM are frequently underrepresented in non-randomly selected populations. Twenty-four percent of subjects had BMIs above 25 kg/m2 compared with 29.2% reported in the 4th Nutrition Report in Switzerland (n = 510).38
Conclusion
Mean FFM peaked in men 35 to 44 y old and women 45 to 54 y old and declined thereafter. Mean FM and %FM increased progressively in men and women throughout the ages studied. The results suggested that the higher weight noted in older subjects is due to higher FM. The percentile data serve as references to evaluate deviations from normal values of FFM and FM in healthy adult men and women at a given age.
Acknowledgements
The authors are indebted to the dietitians at the Geneva University Hospital for data collection.
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This study was financially supported by Foundation Nutrition 2000Plus.