Stay fit and healthy. It is a long way back once you lose it
This is Alex Lightman's answer to the question: how can I burn 5,000 calories in a day?
Ten steps to get you there, based on my details for clarity, which you can abstract and personalise to fit your own metabolism.
1. Develop a regular pattern of sleep and be well rested. Surprisingly few people are able to develop the discipline of going to bed at the same time, getting to sleep quickly, and waking up at the same time refreshed. To burn 5,000 calories a day, you're going to need at least 8 hours of sleep, consistently. Let's say for purposes of this answer that you're going to bed at 10pm and getting up at 6am.
2. Get a Fitbit Surge or other watch that counts heart rate, steps, calories, and allows for custom reads for different activities. Get used to figuring out what your best calories/hour activities are and how much you can do.
4. Walk on a treadmill at an incline for an hour. I am 6′ and 200 lbs, and when I walk at 4 mph and a 6% incline, I burn about 1,000 calories an hour. So one way to reach your goal is to do this for 5 hours (adjusting for your calorie burn based on your own research). Note that this activity is the go-to exercise for contestants on The Biggest Loser. It's not shown for more than 1% of the television show, but contestants have admitted that it's what they spend most of their time doing.
5. If you don't want to walk for all that time, lift weights at 50% or less of max and do many reps, in sets of 10, with long breaks, throughout the day. If you go slow and not heavy, you can get 1,000 or so reps in. Squats are probably your go-to exercise. 60% of the average human's muscle mass is below the waist, so exercises that target the legs give the biggest bang for the buck. It's fairly easy (relative to other things) to do 1,000 squats a day. I have done as many as 3,333 squats in a day (while flying Korean Air business class, which has an empty space in the front of the top deck). I wouldn't be surprised if squats burn 1 to 5 calories each, depending on whether they are weighted or not. 1,000 squats, if you are adapted to them, can be popped off in 20 to 25 minutes.
6. Biking is fun, and can burn 750 or so calories an hour. I have a 38 mile bike ride I do that's mostly on a path by the beach, between Santa Monica and Palos Verdes peninsula, which takes me about 150 minutes, and supposedly (according to my Surge watch) burns 1,600 to 1,800 calories.
7. Rowing lends itself to zoning out, even exercising with your eyes closed, so you can get used to doing it for hours and burn lots of calories while just mindlessly doing the reps. Make sure to use good form, which involves a hard push with the legs. The rule of thumb is 60% legs, 20% core, 20% arms. Rowing spreads the effort out also, so you don't overuse some muscles. Rowing burns about 800 to 1,000 calories an hour for me, but at the higher end, I can only do it for 20 to 30 minutes at a stretch.
8. Swimming is a great way to burn calories if you enjoy it. Don't be afraid to use a snorkel mask and fins if that enables you to swim longer. Swimming does 500 to 1,000 calories an hour in non-cold water. If you swim in very cold water, your body burns calories just to keep your core warm.
9. Wearing an ice vest like the "Cold Shoulder" can burn an extra 200 or so calories. Sleeping above the covers if it's cool or cold will also burn calories, if you are adapted.
10. There are a few biohacks that can burn calories, like cryotherapy. This is available in Venice, California and other places. Exposure to very cold temperatures causes the body to not only burn fat, but to replace yucky white fat (adipose tissue) with brown fat, which is more thermogenic.