# Body composition, anthropometry, and resting energy expenditure in adults with achondroplasia: a pilot study to determine best practices

## TL;DR

This pilot study explores body composition and energy expenditure in adults with achondroplasia to guide weight management recommendations.

## Contribution

The study evaluates the feasibility of using BIA and anthropometry for assessing body composition in achondroplasia.

## Key findings

- BIA and anthropometry can assess excess adiposity in achondroplasia.
- REE is appropriate for body size, suggesting fitness and activity may aid weight control.
- Body fat estimates via BIA align closely with DXA measurements.

## Abstract

To guide recommendations for preferable body weights and energy requirements in those with achondroplasia, particularly given concern for overweight and obesity, studies of body composition, energy utilization, and health outcomes must be conducted in those with this rare (1 in 20,000–30,000 births) condition. We compared body composition using bioelectrical impedance analysis (BIA) and anthropometry against dual energy X-ray absorptiometry (DXA) as a gold standard and characterized resting energy expenditure (REE) among adults with achondroplasia in a pilot study of the feasibility and validity of these approaches and describe implications of their use in this population.

Twenty adults (9 female, 38.5 ± 6.3 years; 11 male, 35.1 ± 10.4 years) with achondroplasia were recruited for a week-long study with an overnight inpatient component to assess the feasibility of conducting tests of health, physical activity, and function. Body composition was assessed using anthropometry, tetrapolar BIA, and DXA under standardized conditions. REE was assessed in the morning in a fasted, resting state and expressed relative to whole body mass and fat free mass. Aspects of body composition were compared by sex using t-tests, and total body fat, percent body fat, and fat free mass by BIA were compared to DXA by linear regression and Bland–Altman analysis.

Height, weight (although ~ 9 kg greater in males), fat free mass (FFM; by DXA or BIA), waist, hip, arm and neck circumference, and REE did not differ by sex; body mass index, total and percent body fat, triceps, subscapular, and arm fat area were greater in females while arm muscle area was greater in males. By DXA, fatness of the extremities was greater in females. Estimates of total and percent body fat were similar by DXA and BIA in both sexes combined and were strongly related to waist circumference.

In achondroplasia, BIA and key anthropometric indicators could assess excess adiposity. We found REE to be appropriate for body size, suggesting that weight control might be dependent on improved fitness and activity levels in this population. Comprehensive assessment of body composition in relation to health outcomes in a larger achondroplasia cohort is required.

The online version contains supplementary material available at 10.1186/s13023-025-03912-z.