Yes. You may be placed on a special pre-operative liquid diet for 1-2 weeks. This diet helps to shrink the liver and to reduce the fat inside the abdomen. This reduces the risk during the procedure.
In addition, some insurance companies might require you to participate in a physician monitored diet program for 3 to 6 months prior to them approving your surgery. This program is more about diet education and demonstrating behavioral changes and willingness to be compliant to the program.