If you eat enough calories you won't lose any weight. MMA training 5 days a week is going to create a huge caloric deficit so you have to balance this out by eating a ton. Depending on your metabolism and how many hours per week you train this could be upwards to 1000 cals. Drinking BCAA's, a protein/simple carb mix, WMS, or simply some gatorade during your training will also help. If your carb-sensitive go with the BCAA's otherwise the protein/carbs would be best. Just sip it throughout your training; it should also keep your energy levels up.
As for integrating weight-training into an MMA conditioning program, train the MMA forum. Those guys should be able to help you out.