BANGKOK (THE STAR/ASIA NEWS NETWORK) - Malaysia Prime Minister Mahathir Mohamad is thinking of writing about how he stays so healthy as he has been asked the same question many times.

"What I did was I observe what happens to me and other people, and I make my own conclusion," said Tun Dr Mahathir on Saturday (Nov 2) at a dialogue session at the Asean Business and Investment Summit in Bangkok.

"It is not very scientific, not proven and not tested, but this is what I observe of the life I have," he said.

The 94-year-old prime minister said this when Thai Asean Business Advisory Council chairman Arin Jira asked him what he ate to keep his mind sharp.

Dr Mahathir said that he did not know how he managed to survive for so long, but admitted that he was lucky he did not suffer from any debilitating diseases.

He added that there was a need to be disciplined when it came to how one ate.

"Don't eat fatty food, too much carbohydrates or too much sugar. You need to be active, and exercise your body and muscles. They must be used or they will be weaker," said Dr Mahathir.

He added that being active also meant using the brain to talk, argue and debate.

"All of this will activate the brain so that it will function well. After you retire, you tend to rest and sleep, and the brain and body will then lose their capacity and the organs will deteriorate," Dr Mahathir added.