Harare - Zimbabwe President Robert Mugabe, who has just turned 91, said on Thursday that one of his secrets to a long life was "not filling my stomach".In a televised interview ahead of a huge birthday party in Victoria Falls, Mugabe said: "I do certain things that I believe sustain life."I eat well, not filling my stomach, eating foodstuffs that I believe sustain one most. You must eat well, and really not go for food because it's attractive and feed yourself until your tummy is full," the longtime Zimbabwean leader said.At least 20 000 guests will flock to the golf course of a luxury hotel for the party on Saturday to feast on elephant, buffalo, donated cattle and a giant birthday cake.Mugabe's half sister, Regina Gata, recently confirmed her brother's disciplined habits, saying he neither smokes nor drinks.The Zimbabwe leader appears robust, though a fall down some steps at Harare International Airport earlier this month reignited questions over his health. He has made several trips to the Far East in recent years for medical check-ups, officially on his eyes.In his first public comments on that fall, the president told his interviewer that he had fallen many times before."In the house you slip, your foot is held by a carpet that is misplaced and so on, or you hit it against something and you tumble," he said."I would want to see a person who hasn't fallen down. I don't see the reason why anyone should be surprised that the president has fallen."Security agents at the airport tried to get photographers to delete images of the fall but some pictures survived, sparking global headlines and a slew of comedy memes.