The actor achieved an absolutely ripped look for the 2017 movie, but Efron insisted he was never going to go back to that level of definition due to the toll it took on his mental health.
The actor put his misery partly down to having to take diuretics - sometimes called water pills - as he had to take Lasix, a drug used amongst bodybuilders that provides them with that 'ripped' appearance.
He also explained that he'd been eating the exact same three meals every day and getting nowhere near enough sleep.
The actor used to get up at 4am to train for Baywatch, and he did that even if filming on the movie had wrapped up at midnight.
Left with insomnia and depression, the whole experience left him feeling burned out and unwilling to put himself through the same misery all over again for another role.
Efron told Men's Health trying to look how he did in Baywatch was really hard work and took a heavy toll on his mental health.
He said: "That Baywatch look, I don't know if that's really attainable. There's just too little water in the skin. Like, it's fake; it looks CGI'd.
"I started to develop insomnia and I fell into a pretty bad depression, for a long time. Something about that experience burned me out."
The actor also recently said he'd stopped following a vegan diet, switching back to eating meat after being convinced by Down to Earth co-host Darin Olien.
He explained that while he wishes he was still a vegan his body 'wasn't processing vegetables in the right way' and decided not to put undue pressure on himself.
This isn't the first time he's said he never wants to get back into the same shape he had for Baywatch, having previously said he doesn't 'ever want to be in that good of shape again'.
It turns out that getting in that sort of shape is actually pretty unhealthy, as it requires you to be dehydrated for multiple days to get the skin pulled really taut over the muscles.
Henry Cavill explained that he went through something similar for The Witcher, as he got into such great shape to play monster hunter Geralt that he tore through his costumes.
However, he revealed that for shirtless scenes he had to dehydrate himself for three days to make his skin thinner which sounds like a thoroughly unpleasant experience.
While there's nothing wrong with putting on a bit of muscle and getting into shape, making yourself look like the stars of the screen takes extra steps which people ought to steer clear from.
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