'You want to know what the secret is? That there is no secret." Brother Colm O'Connell, a retired Irish priest and one of Kenya's top running coaches, is almost spitting with delight as he talks to me. We are standing in the grounds of St Patrick's school in Iten, Kenya. On the grass in front of us, his athletes are going through their warm-up drills. Among them is the tall figure of David Rudisha, world champion and world record holder for the 800m.

Colm may joke about people looking for the secret, but something is going on here. At the 2011 World Championships, Kenya won an incredible 17 medals in the middle-distance and long-distance running events. Even with the heroics performed by Mo Farah and Hannah England, Britain only won three.

In marathon running, Kenyans are even more dominant. In 2011, the world's top 20 fastest runners – in the world's most universal and accessible sport – were all from Kenya. So why, exactly, are they so good?

A few years ago, Mo Farah, one of Britain's greatest hopes for the Olympics, was struggling to even make finals on the world stage. But everything changed for him when he moved into a house in south-west London with a group of top Kenyan runners. "To see them just eat, sleep and train and nothing else was a big shock for me," he said in a recent interview. Farah was already the top British runner at the time, but the level of dedication he saw from the Kenyans was a revelation.

Up in Kenya's Rift Valley there are thousands of runners living like this, training with an intense, almost monastic focus. Every morning, in the town of Iten, where I lived for six months, you can see them everywhere, striding past in a blur of faded wind jackets and Lycra, like commuters in any other city.

"This is the bit people miss when they look for the secret," says O'Connell later, as we watch his athletes race each other up and down a steep hill. Sheer hard work and dedication, that's the key, he says. But can the explanation really be that simple? The answer is both yes and no.

Virtually every Kenyan runner comes from a poor, rural background. From an early age they run everywhere. I had always thought the oft-recounted story of Kenyan children running miles to school every morning was a romanticised myth, but there they are, their pencil cases rattling in their schoolbags, chugging along, sometimes before the dawn has even broken. Daniel Komen, the world record holder at 3,000m, told me: "Every day I used to milk the cows, run to school, run home for lunch, back to school, home, tend the cows. This is the Kenyan way."

One top coach – who has at least six world champions on his books – told me that it takes 10 years of training to build enough of an endurance base to be good at long-distance running. "By the time a Kenyan is 16," he said, "he is already there."

The life of a western athlete, we are constantly told, is one of hard work and sacrifice. But these things are relative, as Farah found out. For the Kenyan runners, hard work is just part of daily life, ingrained in them since birth. Dedicating themselves to running doesn't require any special sacrifice. In fact, in Kenya the life of an athlete is one of relative comfort. Eat, sleep and run. It beats digging the earth all day with a hand plough.

For Kenyans, their focus is sharpened by the success they see around them. Up in the Rift Valley, every village has its star runner, someone who has gone off to win a world title or some big-city marathon, and returned with enough money to buy a plot of land, a cow and a big car. There are role models everywhere. The children look around them and say, when I grow up, I want to be a runner.

So here you have a population who from a young age have been running everywhere, mostly in bare feet – which gives them perfect running form, and stronger feet and legs – and who all aspire to become athletes. Throw in the fact that they all grow up at altitude, which increases the blood's ability to carry oxygen (a good attribute for long-distance running), and eat a diet full of carbohydrates and very little fat, and you have the perfect recipe for producing great runners.

Underpinning all their efforts is the constant spectre of poverty. For every successful Kenyan athlete, there are 10 others training in the hope of success. For them, making it as a runner, even modestly, is their only chance of escape.

Dr Yannis Pitsiladis from the University of Glasgow has spent 10 years studying Kenyans, conducting research into why they are so good at long-distance running. He agrees that it is due to this perfect concoction of factors. I ask him, however, if he can put one reason above the others as the most important.

"Oh, that's tough," he says, thinking hard for a moment. Then he says pointedly: "The hunger to succeed."

"Look," he adds. "My daughter is a great gymnast, but she probably won't become a gymnast. She'll probably go to university and become a doctor. But for a Kenyan child, walking down to the river to collect water, running to school, if he doesn't become an athlete then there are not many other options. Of course, you need the other factors, too, but this hunger is the driving force."

Poverty exists in many other places, and the will to escape it is not unique to Kenyans. The difference, however, is that in Kenya, that will is channeled into running. Every last drop of it.

Many people point to Kenyan dominance in running, and say it must be down to genetics. The big problem with this argument, however, is the lack of scientific evidence. Pitsiladis and others have been conducting research on this for years and have so far come up with nothing. Unless they do, we'll have to continue to concur with O'Connell, that there is no secret, unless you count an incredible level of dedication, borne out of a hard, physical life that, as O'Connell puts it, "makes them strong, disciplined and motivated to succeed".

• Running with the Kenyans is published by Faber & Faber on 5 April, priced £14.99. To order a copy for £11.99 with free UK p&p, visit guardianbookshop.co.uk