The exercise part is possible in theory, but in practise not many people have lives in which they can do 4000 kcal of exercise daily, six days a week. 4000 kcal takes a long time. I have heard of a guy who became a security guard and walked around a town for 10 hours each night. Exercise took him from "severely obese" to just above "normal" BMI over the course of 18 months or so.

The diet part is also possible in theory, but many people's family and social environments practically require them to eat muffins, cakes, sweet desserts, and other micronutrient-poor dishes. Refusal to take part gets them ostracized.