The 'X Factor' judge topped the scales at 224 lbs at his heaviest but is now in the best shape of his life but he won't relax his exercise and diet regime in case he starts to gain the weight again.
Gary told The Sun newspaper: "I still think of myself as a fat guy, I've had it under control for a few years but it's hard. I can't relax I can't ever think I'm slim."
The 42-year-old musician turned to comfort after his failed attempts to launch a solo career when Take That split up in 1996 after six years together.
Gary recalled: "I thought my life was over. All I could think was that after going round the world, having hit after hit, the whole thing had stopped and I was actually qualified for nothing. Nothing prepares you for the fame but nothing prepares you for what happens when it all stops. People literally won't speak to you."
Gary once again conquered the charts when Take That reformed in 2005 achieving critical acclaim and performing huge stadium tours.
The star admits he found it difficult to deal with the success of his former bandmate Robbie Williams, who went on to have seven number one solo albums in the UK after he left Take That to go solo in 1995.
He said: "I don't think a day went by when I didn't think about Robbie. I was completely tormented by that."
Gary - who asked Robbie to rejoin Take That for their 2010 album 'Progress' and is now good friends with him - claims Sir Elton John was one of a few celebrities who he kept in contact with during that time.
He revealed: "It meant a hell of a lot to me and still means a lot."
Gary and Elton have recorded a duet, 'Face to Face', for his new solo album 'Since I Saw You Last'.