Differential investment in body girths by sex: Evidence from 3D photonic scanning in a Thai cohort.

OBJECTIVES: Life history trade-offs may manifest between competing organs and tissues in the body. Sexual dimorphism in tissue investment is well-established in humans, with sex-associated body shape differences linked to natural and sexual selection. This study uses three-dimensional (3D) photonic scanning to test whether males and females differentially invest energy in various body regions in relation to two independent proxies of growth.

MATERIALS AND METHODS: Body shape data (multiple girths) came from a Thai cohort (n = 11,610; 53% female; age range 21-88 years). Weight was considered a proxy for recent energy acquisition. Stature represented completed growth, a proxy for energy acquisition earlier in life. The data were analyzed using growth-proxy by sex interaction log-log regression models adjusting for age, salary and number of children.

RESULTS: For a given percentage increase in weight, females showed greater percentage increases than males in girths of the arm, chest, hip, thigh, knee and calf (p < 0.001), whilst males exceeded females in head and waist girths (also p < 0.001). For a given percentage increase in height, weight and all girths showed greater proportional changes in males than females (p < 0.001).

DISCUSSION: These results indicate sex-specific life history strategies wherein the direction and timing of energy investment in girths varies between the sexes. The results add to literature suggesting that sexual dimorphism in body morphology is not a fixed trait; rather, differential energy allocation to specific body regions appears to be a plastic strategy adjusted in relation to energy acquisition across the life course.