Hi and thank you so much for this query. Weight gain would not cause selective swelling of the calves and ankles. One common cause of weigh gain and edema of ankles is hypothyroidism. If you have symptoms like constant fatigue, constipation, dry skin, etc, then you may be having a thyroid problem. Other possible causes are varicose veins. However, get a detailed interrogation and clinical evaluation to establish the cause and treat adequately. Do you have any other disease condition? If so please report it to me for more insights and suggestions. I hope this helps. I wish you well. Thank you so much for using our services and do feel free to ask for more information and clarifications if need be.