How to lose 50lbs in 1 week:
Step 1: Be clinically obese, preferably 500lbs+ so as to make it that much easier to create a massive caloric deficit.
It takes 3,500 calories to lose 1 pound. At 500lbs, the calories you need to maintain your weight would be: Bodyweight (500) x 15 = 7,500 calories/day...that leaves more room to lose more weight.
Step 2: Eat nothing the entire week. This would let you burn 7,500x7 = 52,500 calories for the week, which would burn 15 pounds. You'd likely lose an additional 5-6 pounds of water weight as well. So lets say 20 pounds total.
Step 3: Where are the other 30 pounds going to come from? Cardio of course! 1 hour of cardio burns 500 calories.. 7 hours of cardio would burn 1 extra pound...So!
You would need to do 210 hours of cardio this week, which is 30 hours per day....WOOPS, there are only 24 hours in a day.
Well damn, guess this is not possible!
It's best to be more realistic in your weight loss goals, educate yourself on what is and is not possible, then follow a sound strategic diet plan to see the best results in the fastest time possible.