Fat mass to fat-free mass ratio reference values from NHANES III using bioelectrical impedance analysis

Clin Nutr. 2018 Dec;37(6 Pt A):2284-2287. doi: 10.1016/j.clnu.2017.09.021. Epub 2017 Oct 6.


Background & aim: Low fat-free mass (FFM) or high fat mass (FM) are abnormal body composition phenotypes associated with morbidity. These conditions in combination lead to worse health outcomes, and can be identified by a high FM/FFM ratio. Here, we developed sex, age, and body mass index (BMI) stratified, population-based FM/FFM reference values using bioelectrical impedance analysis (BIA) measurements.

Methods: White, non-Hispanic individuals aged 18-90 years old with data for weight, stature and BIA resistance measures from the third National Health and Nutrition Examination Survey (NHANES) III were included. Previously validated and sex-specific BIA prediction equations were used to calculate FM and FFM. FM/FFM values were generated at 5th, 50th and 95th percentiles for each sex, age (18-39.9, 40-59.9, 60-69.9 and 70-90 years), and BMI category (underweight, normal weight, overweight, class I/II and class III obesity).

Results: A total of 6372 individuals who had estimated FM and FFM values were identified (3366 females, 3006 males). Median values of FM/FFM were 0.24 and 0.40 for young (≤39.9 years) males and females with normal BMI, and 0.34 for males and 0.59 for females who were overweight. For elderly individuals aged >70 years, median FM/FFM for males and females were respectively 0.28 and 0.45 for those with normal BMI, and 0.37 and 0.61 for those in the overweight category.

Conclusions: These FM/FFM reference values provide information on body composition characteristics that account for age, sex and BMI, which can be useful to identify individuals at risk for body composition abnormalities.

Keywords: BIA; Fat mass; Fat-free mass; NHANES.

MeSH terms

  • Adipose Tissue / physiology*
  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Body Composition / physiology*
  • Body Mass Index
  • Electric Impedance*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Nutrition Surveys*
  • Reference Values
  • Young Adult