Originally Answered: How do i lose weight fast and gain muscle fast?
To lose a lot of body fat, you need to do cardio. To gain a lot of muscle, you need to do resistance training. However, that's a very broad and sweeping answer, so let's go more in depth.
To lose fat, your best bet is roughly 20 minutes of High Intensity Interval Training followed directly by 15 - 30 minutes of less intense cardio. An example of this would be 20 minutes of alternating slow jogs (1 minute each) & increasingly fast sprints (30 seconds each), followed by 15 - 30 minutes of brisk walking.
To build muscle, you want to do circuits that work the full body or make a reasonable split. Some exercises to try include squats, deadlifts, push ups, chin ups, etc. If you're shooting for a six pack, you'll want to include renegade rows, lying straight leg lifts, planks, & side planks.
Now for diet, which is probably the most important issue in reaching your goals. First of all, try the paleo diet, you'll be stunned at the difference it makes. Next, to assist with the fat loss & calorie deficit, add 1 or 2 separated days of fasting a week (as in on those 1 or 2 days you only have water for most of the day and a healthy, well proportioned dinner). Finally, you'll want to increase water intake to flush out the excess sodium in your body.
For foods to reduce (or better yet, cut) from your diet, I'd say sugars, over-processed starches (white bread, pasta, rice, etc.). If anything you'll probably need to increase your protein intake a little as well (lean proteins such as chicken).
Hope this helps.