Hi. Lantus (or Levemir) by itself doesn't cause weight gain but as it causes the body to have adequate insulin and hence able to convert carbs to energy you have to control the amount of carbs. Adding a fast-acting insulin or changing to a mix might help keep blood sugar down but it won't help with weight. I'm afraid keeping the carbs right down should help. Many of us set a limit of, perhaps, 150gm/day and some have a much lower limit. Set yourself a target limit and see how you go.