Koia-Hamling is frank about the difficulties he encountered in trying to turn his back on unhealthy living.
"Like most people, at high school [I] did the party thing and that carried on into my early 20s," he says.
"I'd been working in radio in Taupo but moved to Christchurch so my wife could go to teachers' college. I couldn't find any radio work there, so I was working in factories and supermarkets. That affected my attitude and I just didn't care about my body or anything.
"I smoked at least a packet of smokes a day, did no exercise and drank Coke by the bucketful."
His first step to turning things around was getting involved in social touch rugby.
"I've always been competitive. I knew I could run fairly decently and touch reminded me that I actually liked being out there, running around and trying to be fit."
Koia-Hamling decided to quit smoking shortly afterwards, but it had an unforeseen consequence. In a blog post, he writes: "I needed something else to replace the ciggies ... that was food. Every time I wanted a smoke I'd eat something instead."
The result was dramatic - in the course of four or five weeks he shot up from 66kg to 99kg. So the health issues continued.
"The breathing got better and I could taste food," he says of giving up smoking. "I just needed something to do with my hands and mouth and eating happened to be the next easiest thing to do.
"That was pretty gross. It would have made more sense if I had gone for a run every time I wanted a smoke."
Koia-Hamling says he was forced to do something about the weight after looking in the mirror one day.
"It's always when you see yourself nude, competing with your wife for breast size," he laughs. "I was able to balance a bowl on my tummy. It was funny at the time, but it's actually pretty gross just sitting there with a pudding bowl resting on your stomach."
The changes came gradually. Koia-Hamling and his wife lived in a rural part of Christchurch so they used to walk the acres of farmland surrounding their house. From there he started to compete in fun runs, and after moving to the North Island he joined the Hamilton City Hawks running club.
"That's when I went from casual running to going twice or three times a week and being introduced to speed work and hill work. That was the start of feeling like a proper runner."
Koia-Hamling has gone on to compete in several long-distance events. His achievements include finishing the Rotorua half-Ironman and setting a Guinness World Record for the fastest half marathon in an animal (kiwi) costume.
And with running came weight loss. Koia-Hamling says he's currently around 72kg, but hopes to get down to around 69kg before he races the 16km course on the Hillary Trail.
One strategy he has adopted to keep trim is to not forgo his favourite treats entirely, but to use them as rewards for hard work.
"On Sunday I'll go for a long run and my treat is to read the paper and have a couple of peanut butter sandwiches and a Lift Plus," he says.
Koia-Hamling knows how difficult it can be to start running and leading a more active lifestyle. He says the key to it is not being embarrassed or worrying what others think.
"The first step is to get out the door, and once you start running you'll be surprised that most people don't give a crap - they don't care [about] your running stance or what you look like. People aren't going to be looking at [you] and laughing."
Western trail
What: The Hillary Trail, Waitakere Ranges, Auckland.
When: Saturday, March 14.
Distance: Course distances vary. Competitors can take on either the 80km, 34km or 16km courses
For more information about the race and Caleb's blog, visit: http://thehillary.co.nz/wordpress
