The Athletic's Mike Sando spoke with 50 coaches and talent evaluators to rank the likely starting quarterbacks for 2020. Newton sat 19th on the list.
The former Carolina Panthers star explained in March 2019 how he was changing his diet and going vegan.
The anonymous coach told Sando he thinks the shift could backfire:
"I don't think he is Superman any more. Remember when (Colin) Kaepernick became vegan, changed his body and he just wasn't as dynamic of an athlete any more? Cam was 265 and bigger than everybody. He looks skinny now, like he is 235 and wants to have ripped abs, and that's his choice. Is he going to have that power running element?"
Recent history would suggest playing at a lighter weight won't hurt Newton all that much.
The Charlotte Observer's Joseph Person wrote in July 2017 that Newton had weighed in at 246 pounds, 14 pounds below his usual weight. He proceeded to run for a career-high 754 yards and averaged 5.4 yards per carry during the 2017 season.
Bringing up Kaepernick as some sort of cautionary tale is a bit of a misnomer, too.
Kaepernick explained in August 2016 how the weight loss he experienced was due to surgeries he underwent on his left shoulder, right thumb and left knee—not the result of a vegan diet. Kaepernick remained a dynamic runner as well. He ran for 468 yards and two touchdowns in 12 games that season, and his 6.8 yards per carry were a personal best.
It's fair to wonder whether Newton can be the same kind of player he was in 2015, when he won an MVP and guided the Panthers to the Super Bowl. He had shoulder surgery in January 2019 and foot surgery in December. He's also the all-time leader in rushing attempts (934) for a quarterback, and his 291 sacks are the sixth-most since he entered the league in 2011.
The Panthers relied heavily on Newton during his nine-year run in Carolina, which put a ton of mileage on his body.
If his days as a two-way threat are over, his previous workload is probably a far bigger reason why, not his lighter weight.