Here's Noah Spence on his diet at training camp to gain weight. 9,000 calories a day!
https://www.espn.com/blog/tampa-bay-buccaneers/post/_/id/20957/nine-meals-9000-calories-a-day-helped-noah-spence-gain-35-pounds
"Today was the heaviest I've ever been and I felt great. I was 263 today," said Spence, 24, whose goal was to put on the weight cleanly, with minimal gain in body fat. "I kind of just started playing with it [in the offseason] to see what works. I felt like if I just don't stop eating or drinking, I won't lose weight."
https://www.nhpr.org/post/gain-weight-nfl-player-eats-7000-calories-day#stream/0
GREENE: Seven thousand calories. When training camp started, he weighed about 270 pounds, and he's trying to get up to 290. He's now halfway there - throwing back eight protein shakes a day a whole lot of chocolate milk - 10 more pounds to go before the Redskins season opener on September the 9th.
My roommate in college was a tight end and he was doing this same thing during their summer camp. He was a freshman and wanted him to put on about 20-25 lbs by the end of camp...he was drinking an insane amount of shakes. We started making him buy his own milk lol because he was using way too much.
He did it and we could see the difference every few days.