Can you recommend a diet for fat loss and muscle gain?

Yes: To lose fat, eat less calories than you need. To preserve muscle, be physically active and try to use all muscle groups, large and small. Being active most days of the week, is important to maintain muscle mass, while losing fat. You can be active even 5 minutes a hour, while sitting at a desk job, It can add up at the end of the day to 30 to 40 min of activity.