Adult fat content: reinterpreting and modelling the Benn Index and related sex differences.

BACKGROUND

In women, the height exponent, p, of the Benn Index, (body mass)/height(p), is typically lower than in men, body masses are more weakly correlated with height and fat masses tend to be higher. In both sexes fat masses correlate only weakly with height. Changes in fat mass are typically accompanied by changes in fat-free mass.

AIMS

To integrate these facts, together with other published findings relating to fat content and to explain why p is lower in women.

METHODS

Data and statistics are taken from the literature. The differences in p are explored by Monte Carlo and algebraic modelling. Mean transverse areas of the body (MTAs), calculated as (body mass)/height, are related to height.

RESULTS AND CONCLUSIONS

The body can be modelled as consisting of a component, M1, varying roughly with the cube of height and another, M2, varying little with height. The low correlation between total body mass and height is due both to M2 and to data scatter. The low p values in women relate especially to M2. Relationships amongst height, fatness, MTAs and girths of body parts generally conform to this interpretation. Questions are raised as to how health risks are best related to fat mass.