"I was a very fat kid," he confesses.
"I was chubby and then one day I thought, 'Stuff it, I am not doing this anymore, I don't want to be the chubby kid'. And so I cut out carbs and I cut out sugar and I realised what I was doing was Paleo and so I went full, big into it and I lost so much weight, I toned right up."
It's been such a way of life for the 25-year-old for so long that he says he was very close to sticking to Paleo when it came to their cooking in the competition.
"I think the biggest struggle coming into My Kitchen Rules I had was do I bring Paleo food to the competition," he says.
"I wasn't as confident as I wanted to be especially with Pete [Evans] being there so I stuck to food that we knew but I'm back on Paleo."
Given Josh, and now Austin – who also tries to stick to a Paleo diet with his brother – are pretty strict when it comes to their diets at home, they admit it was tough having to eat all kinds of food while on MKR.
"During the Instant Restaurant rounds, me and Austin both lost a lot of weight because it was so stressful and the eating times are very strange," Josh explains.
" But then during the challenge phase, we put on a few kilos each because we were practising so much and we were eating our food.
"But now that we're finished with My Kitchen Rules, me and Austin are Paleo."
For more reality TV goss, listen to the newest episode of reality TV podcast Real Talk with Holly & Ali below.