(CNN) — Ben Okeke has a heavyweight challenge on his hands — trying to popularize the ancient Japanese sport of sumo wrestling, in Nigeria.

Okeke, also known as “Baba Mutum” — which means “very big man” —runs a sumo academy in Enugu, Nigeria, where he teaches about 40 students.

Okeke started out as a professional wrestler until a friend suggested he take up sumo, so he packed his bags and moved to Japan in pursuit of a new challenge.

The sport became his life passion and in 1996 Okeke won a world championship bronze medal — the first such achievement for a Nigerian. The match changed his life.

“When I won that medal I felt good because I was coming back as a proud guy, because of my sweat,” Okeke told CNN.

“When I came back to Nigeria everything was like a new life. People wanted to know me more, people wanted to associate with me just because I had that medal.”

Wrestling is a traditional sport in many parts of Nigeria, but the ancient Japanese art of sumo is almost completely unheard of there. But from his makeshift arena in a rented hall, Baba Mutum believes Nigerians have what it takes to compete on the world stage

“I know Nigerians can do sumo better than other countries that are doing it now, because we have strong people, and the kind of food we eat here gives us an advantage over other areas that take light food,” Okeke said.

But Okeke faced one of his toughest challenges after a knee injury meant he had to stop professional sumo in 1997. His weight was no longer an asset — it was a burden.

“My weight was growing,” said Okeke. “It came up from 250 kg, 260 kg, to 350 kg. It was disturbing.

“For me to do things for myself was becoming very, very uncomfortable. I went in to do surgery to control the weight increase, so I did the gastric bypass. It was three years ago, so that’s why I’m having a new look today.”

Okeke said sumo is not just about how much you weigh — it’s about how hard you work. That’s something he teaches his students.

Bright Udo is one of Okeke’s students in Enugu. “I like the game,” he told CNN. “People like us, we can do it perfectly. So with the encouragement of my coach, I believe I can go forward.”

Another student, Emeka Okarama, said “You have to be strong, to have stamina. You have to have the capacity to contend with the strength of your opponent. You have to be fit and have what it takes to be a man.”

Okeke said, “People think it’s a big man’s game — sumo is a brain game.

“You have to be disciplined — everything is in sumo. I love sumo so much that if I come in my next like I want to be a sumo wrestler.”