He weighed in at 130kg on Sunday when he entered The Sun-Herald City2Surf, presented by Westpac, for the first time. He plans to lose another 30 kilograms in time for the New York Marathon, which he intends to enter, in November.

Peter O'Davis, 64, was a 20-schooner-a-day drinker and weighed 189 kilograms until he went "cold turkey" six years ago. He was a brawny 117 kilograms when he ran his first City2Surf on Sunday.

Between them, these two men have already shed more than 100 kilograms. They have never met, but both are running for their lives.

"Most of my family is morbidly obese," says Leha, the son of an Aboriginal mother and Tongan father.

A succession of deaths in his family from "lifestyle diseases" got him worried. The death from cancer of his 24-year-old brother Tohi – the fittest in the family, who had strong prospects as a rugby league professional with the Cronulla Sharks – motivated Leha to change.

In March he applied to join marathon legend Robert de Castella's Indigenous Marathon Project.

"I thought there was no way they'd call," he said. "I was too obese."

They called. At his first 5km trial, Leha walked most of it. Four weeks later, he ran 10km in an hour and 20 minutes, then a half-marathon. He's training for a 30km run in Alice Springs in September and, if it goes well, he has a strong chance to be selected for the New York marathon.

When he finished the City2Surf in about 90 minutes on Sunday, de Castella was there to cheer home Leha, from Marrickville, and another nine Indigenous runners who hail from far afield as Thursday Island, Arnhem Land and Timber Creek.

"This is transforming lives," de Castella said. "An ad for healthy living is all well and good, but this is Indigenous people becoming leaders and role models for their own communities."

Leha's nephews have started running with him.

"It makes me teary just talking about," he said. "I am proof that you can change; you can do anything if you put your mind to it."

Peter O'Davis didn't mind a drink or 20. He was a publican, and he admits: "I consumed too much of my own product."

On the morning after his 58th birthday, however, he stopped.

"I fought for my country in Vietnam, but suddenly I decided I had to fight for my own life. If I wanted to see my grandkids grow up, something had to change."

His inspiration was his son, the former Knights fullback and State of Origin star Robbie O'Davis. Peter joined Robbie's boot camp in Newcastle.

Robbie and his children were on the finish line on Sunday to watch O'Davis run home.

"My only regret," O'Davis said, "is I didn't do it all sooner."