That is an excellent question and one that is best answered by your primary care doctor
or other medical care provider. It is difficult to know what your current weight is and what your goal or healthy weight range would be, so your doctor will best be able to evaluate you and offer guidance on what dieting you should do to get to your goal weight. That being said, it is not recommended that you allow your weight to fluctuate greatly as you are describing but rather that you attempt to control your portion size, even in during the holidays when this can be very difficult, to ensure that you do not have large variations in your weight. This can lead to a variety of problems and also will make it more difficult to lose the weight once you have gained it, so rather than allow yourself to gain a lot of weight and then work to lose it, it is recommended that you practice moderation and then not have such fluctuations in your weight which can then become very difficult to lose after the holidays are over. It is best that you discuss a proper and healthy diet plan with your doctor.