Endocrine Abstracts

Aim: The sex hormones initiate profound physical and physiological changes during early puberty, but to what extent are they responsible for continuing the body composition changes of late adolescence? We aimed to examine the effect on body composition of sudden sex hormone withdrawal to gain insight into their action.

Patients and Methods: Thirty six healthy phenotypically and chromosomally normal postpubertal individuals aged 15–17 years with gender dysphoria (M=11; F=16) underwent Tanita body composition analysis at 0, 6 and 12 months during reproductive hormone suppression with triptorelin (Gonapeptyl Depot 3.75 mg) 4 weekly as part of the standard therapeutic protocol. Sex hormone suppression was assessed biochemically.

Results: The effect on body composition differed between males and females. Values quoted are group means. Females gained weight +3.5 kg due to fat deposition (3%), with a BMI increase of +1.2 kg/m² over the year. The BMI, however, fell in males by −0.25 kg/m²; the small weight gain 0.4 kg being counterbalanced by a 1 cm height increase. Changes in fat free mass were small: −0.35 kg in females and none overall in males. Basal metabolic rate fell rapidly in females by 200 kJ/day. For males in contrast, although the fall was greater, −240 kJ/day, but this did not occur until the second 6 months on treatment.

Conclusions: The body composition changes on sex hormone withdrawal in mid-adolescence are much less marked than in the equivalent state in late middle age, and differed between the sexes. In particular the expected loss of the lipolytic and anabolic effects of testosterone were not seen. It is possible, therefore, that other factors, such as the relatively higher GH production inferred from the continued growth in males may preserve body normal body tissue balance, even in the absence of sex hormone secretion, and this requires further study.