Latitudinal Gradient in the Body Mass Index (BMI), and the BMI's Geometric and Statistical Relationships to the Surface Area: Volume Ratio and Body Shape

Author

Brandy Lea O'Neil, University of Tennessee, Knoxville

Date of Award

8-1998

Degree Type

Thesis

Degree Name

Master of Arts

Major

Anthropology

Major Professor

Andrew Kramer

Committee Members

Lyle W. Konigsberg, Richard L. Jantz

Abstract

The body mass index (BMI), weight/height² (W/H²), is currently the index of choice for assessment of nutritional status. Statements in the literature about the BMI as a potential expression of “cold adaptation” or “Bergmann’s Rule” beg the question: What does that BMI measure in terms of size, shape, and the surface area:volume (SA:V) ratio? Geometric modeling shows that the BMI captures both size and shape and is inversely related to the SA:V ratio. This admixture of size/shape information, combined with the unmeaningful absolute value of the BMI, preclude precise understanding of what it measures. A new weight-height-based variable was derived –the mean effective breadth (MEB)- which more clearly relates to the SA:V ratio and heuristically represents what weight-for-height does: it alters body breadth.

Previous findings of a geographical cline in the BMI in Native Americans were expanded to a worldwide sample of 328 adult populations. The BMI and MEB increased with increasing latitude, while the SA:V ratio decreased. All three ratios were also correlated with variables that alter the biological SA:V ratio: sitting height, relative sitting height, and bi-acromial and bi-iliac breadths. The MEB showed higher correlations with latitude, weight, height, sitting height, relative sitting height, and bi-acromial breadth than did the BMI, though coefficients were similar to those of the SA:V ratio.

The BMI’s geometric and statistical associations with the SA:V ratio and measures of proportion or shape corroborate and amplify others’ findings that the BMI is not a shape-independent index of body size or nutritional status. The W/H² ratio was originally conceived by Quetelet as a “proof” of body proportionality. Nutritional epidemiologists should beware these associations when using BMI cutoff categories to diagnose chronic energy deficiency or obesity.

Recommended Citation

O'Neil, Brandy Lea, "Latitudinal Gradient in the Body Mass Index (BMI), and the BMI's Geometric and Statistical Relationships to the Surface Area: Volume Ratio and Body Shape. " Master's Thesis, University of Tennessee, 1998.
https://trace.tennessee.edu/utk_gradthes/4230