Once you arrive at: "and achieved a weight of 191 pounds, yet six years later, after regaining 100 pounds of that lost weight, had to consume an 800-calorie-pe

Once you arrive at: "and achieved a weight of 191 pounds, yet six years later, after regaining 100 pounds of that lost weight, had to consume an 800-calorie-per-day diet to maintain his weight." You should just take a step back and look at your assumption. The contestant either wasn't able to count calories, was in medically induced coma or more likely was just deluding themselves about their calorie intake and/or lying about it. "Metabolism slowing down" is such a nonsense term as well. Like how does it matter if your body gets slower at processing food? Maybe the body becomes a bit more efficient but that's about it. It's a good thing. It won't magically start producing energy from the sun though. Like if you ever were around competitive athletes who care about their diet you would instantly see how nonsensical the thesis is. People struggle to eat enough to not lose weight. They eat as much as the body can process during activity (currently 90/120g of carbs per hour is a new normal at high level) and then eat a lot after to replenish their glycogen and lost fat. They would kill for "metabolism slowing down" allowing you to function on 800 kcal per day but no such thing was ever observed. We know quite well how much the body burns during activity. It's normal to burn 500-1000kcal per hour (or more at pro level) on a bike or running and you need to eat enough to cover that if you want to sustain your training volume. Harvard publishing "people are clueless about their calorie intake but let's assume they aren't and reason from there" kind of "research " isn't good for their credibility.