In boys treated with a long‑acting GnRH‑analogue (leuprolide) for early puberty, overall body‑mass‑index (BMI) stayed about the same during the first two years, then dropped after treatment ended. Kids who started at a normal weight tended to gain weight in the first year, while those who were already overweight or obese mostly kept their weight or even lost it. By the time they reached adult height, normal‑weight boys were back to their original BMI, overweight boys stayed the same, and obese boys ended up lighter.

Existing data regarding effects of long-acting gonadotropin-releasing hormone analogues (GnRHa) on body mass index (BMI) in boys with idiopathic central precocious puberty (iCPP) are inadequate. Evaluating the effect of GnRHa on BMI in boys with iCPP during and after treatment completion at final height (FH) was aimed. Eighty boys with iCPP who completed GnRHa (leuprolide acetate, 3.75 mg (every 4 weeks)) were enrolled. Auxologic measurements were conducted at the beginning and yearly until treatment completion, then at FH (7.0 ± 1.3 years after treatment completion) in 58. Subgroup analysis were conducted according to pretreatment BMI status (42.5%: normal weight (NW), 30.0% overweight (OW), 27.5% obese (OB)). Mean BMI-SDS (1.3 ± 0.9) remained unchanged until 2nd year (1.5 ± 0.7 SDS, 1.3 ± 0.7 SDS, p = 0.956, p = 0.978) then decreased at FH (0.9 ± 1.5 SDS; p = 0.000). In NWs, BMI-SDS increased during the 1st year (0.5 ± 0.8 SDS to 1.2 ± 0.7; p = 0.031). In OBs, it decreased during the 2nd year (2.3 ± 0.6 to 1.7 ± 0.9; p = 0.000). BMI-SDS at FH returned to pretreatment in NWs, remained the same in OW, and decreased in OBs (p = 0.001). Adult BMI-SDS positively correlated with pretreatment BMI-SDS (r = 0.477, p = 0.001).  Increase in BMI-SDS during the first year of GnRHa was only observed in NWs while OW and OBs maintained BMI-SDS. During adulthood, this increase of BMI-SDS in NWs was reversed while OBs exhibited a significant decrease. Lifestyle and diet programs should be implemented to NWs as well as OW and OBs boys with iCPP when initiating GnRHa treatment. • Fat and lean mass increase with a striking sex difference during physiologic puberty. Suppression using GnRHa treatment in boys with CPP is expected to have implications on body composition; however, existing data are insufficient. • Depending on pretreatment BMI status, GnRHa treatment has varying implications on BMI-SDS in boys with iCPP. NW boys have a higher risk of weight gain; thus, NW boys and their families should be counseled on this risk and management strategies (healthy dietary and physical activity) at the beginning of GnRHa treatment as should OW and OB boys.