Comment by darksaints

3 years ago

I believe him. As a nowhere-near-olympics division 1 swimmer, I had developed a major weight loss problem my freshman year. I actually was required to log my calories and meet with a sports nutritionist weekly. After 6000 calories a day, I was shoving so much food in my mouth, I felt like it wasn't possible to eat any more than I did. She prescribed Snickers bars as a way to top off my calories every day without contributing too much to feeling full. I was targeting 7000 calories a day, and I don't think I ever consistently reached that goal, but around that time my weight stabilized.

There are a lot of people who maintain a high degree of fitness, and for them I can imagine 4000 calories is about right. But there are some types of training that are consistently pushing your physical limits. I don't have any sort of data to back this up, but it has long been my theory that the reason why elite athletes can burn so many calories is because they aren't actually burning them in the traditional sense of cells oxidizing chemical energy to create work...they've crossed over into the territory of muscle tissues being torn up and resynthesized so much that your body can no longer do so efficiently.

As an analogy, typically in manufacturing there are always efficiencies that can be extracted. But in very mature industries where there aren't any easy efficiencies to eek out of the system, you have to start making tradeoffs. One common tradeoff is throughout vs yield. You can increase your throughout, but in order to do do so, you have to cut corners on processes and subsequently increase the total amount of waste in the process.

And as a "maybe this is related" data point: 82% of marathon runners suffer from Acute Kidney Injury. Your kidneys have one job: waste disposal. It would be easy to infer that at the boundaries of human conditioning, the kidneys aren't up to the task of processing all of the waste that the body is producing.