Are males with Klinefelter syndrome (KS) more prone to weight gain?
Recent research has shown that males with Klinefelter syndrome (KS) have increased body fat and reduced muscle mass. However at this time, the cause of the increased body fat, especially in the abdominal (stomach) area, is not known. Some medical researchers believe it may be caused by the hormone imbalance due to hypogonadism. Others believe the increased body fat may be caused by genetic factors due to having an extra X chromosome since the body fat begins to appear in childhood before the hormones of puberty would play a role. Still other medical researchers believe it is a combination of both testosterone levels and genetic factors. In a recent study of males with KS, testosterone therapy only partly corrected the unfavorable muscle/fat ratio, however some researches believe this may have been because the testosterone doses were too low. In addition, males with KS also have lower aerobic capacity (ability of lungs and heart to get oxygen to the muscles during exercise) and reduced muscle strength in both biceps and quadriceps muscles. This may decrease the amount of exercise a male with KS can do, which might increase the risk of weight gain. At present, no studies have studied the effects of testosterone treatment on muscle strength or other measures of physical fitness in males with KS. 
Men with KS, especially those with increased weight in their abdominal area, are at an increased risk for type 2 diabetes and metabolic syndrome. Therefore if you are having difficulty losing weight, you should make certain your doctor is screening you for these conditions.
Last updated: 1/31/2016
Is there a way for men with Klinefelter syndrome (KS) to lose the extra weight?
We were not able to find any published, successful ways to help males with KS lose the extra body fat. Some medical researchers support testosterone therapy, but as noted above, there is no evidence as of yet that this will help decrease weight. In addition, testosterone supplementation does not work for all males with KS.
However since this is a relatively common problem for men with KS, you may want to contact a nonprofit support and advocacy organization focused on KS for an answer to your question. Other members of an organization who have KS may be able to tell you what has worked for them and what has not. The medical advisory board may also know of unpublished information which may help you. We have several groups for KS listed under the Organization section.
Last updated: 1/31/2016
We hope this information is helpful. We strongly recommend you discuss this information with your doctor. If you still have questions, please
Aksglaede, L., Link, K., Giwercman, A., Jørgensen, N., Skakkebæk, N. E. and Juul, A. 47,XXY Klinefelter syndrome: Clinical characteristics and age-specific recommendations for medical management. Am. J. Med. Genet.. February 15, 2013; 163C(1):55-63. http://www.ncbi.nlm.nih.gov/pubmed/23345262.