The athlete took to Instagram to inform his 10.8 million followers that he's decided to 'bulk up' after driver weight rules for the 2019 Formula 1 season have loosened.
Hamilton, who revealed that he'd adopted a plant-based diet back in September 2017, states he has gained 15lb, going from 68kg (150lb) - a weight he has had to maintain for the past 12 years - to 75kg (165lb).
'Wish I did it sooner'
"Adding weight was easy and I did this on a vegan diet. People say 'oh I need my protein and that's why I could never go vegan'," he wrote.
"I have plenty of protein in my diet and I've gained muscle, and I'm healthier and happier than I've ever been. Wish I did it sooner."
'I choose to love'
This isn't the first time Hamilton has spoken out about veganism. Last year he blasted the meat industry for 'animal torture' on Instagram, saying: "Every bit of meat, chicken, or fish you eat, every bit of leather or fur you wear, has come from an animal that has been tortured, pulled away from their families and brutally killed.
"We all have choices to make and if you are ok with it, then that's you, but I choose to love, to be conscious of what I'm supporting and I refuse to support the companies that buy from those companies killing and torturing animals."