As one of Ireland's best-known ultra-athletes, he has pushed his body to the limit on numerous occasions.
But marathon man Mark Conlon has revealed an unlikely secret behind his epic achievements - takeaways from the chipper.
The super-fit Dubliner said a regular intake of fast food, including chips and pizza, has played a key part in fuelling his many successes and also helped him remain injury free.
The 36-year-old's most notable feats include running a record-breaking 33 marathons in 33 days, and a punishing challenge which saw him cover 50km a day on foot for 22 days.
And now, as he counts down the days to another gruelling charity event, running 10 marathons in the same number of days to raise funds for the homeless, he insisted he'll be sticking to his tried-and-trusted diet of calorie-laden grub.
"I eat healthily enough, but I also enjoy pizza and going down to the chipper," he said.
"But this works for me when I'm racing because you burn the bad fats off during the race. I think the way I eat helps my body recover. I've also never collapsed during a race, and I put that down to my diet. So certainly the diet I have works best for me."
Clondalkin native Mark, a security officer on Dublin's tram network, starts his marathon challenge on April 12 to raise money for the charity Inner City Helping Homeless.
"I've seen the suffering out there first-hand, and it's getting worse. The Government is simply not doing enough to help the homeless," he continued. "There are more families with young children on the streets, and there's nowhere for them to go because the hostels are too dangerous.
"I work on the Luas and I see dozens of homeless people sitting in the trams every day because they've nowhere else to go, and because they're trying to keep warm.
"I talk to them all the time and my heart goes out to them because they're in a living nightmare."
Ex-soldier Mark, who is looking for sponsors, said completing the 10 epic runs would be tough, but "nothing like what people who are out on the streets go through every single day.
"I want to raise as much as I can as every cent will go to the homeless. The staff are all volunteers and are out every night handing out meals."
For details on how to donate, see 10 Marathons in 10 Days for Inner City Helping Homeless on Facebook.