The Take That frontman piled on the pounds following the boy band's first split in 1996 and admits it became so bad he was having trouble doing every day tasks.
The father-of-three – who recently celebrated his 10th wedding anniversary with wife Dawn – said: "For a couple of years in the late 90s I suffered with depression and I ballooned to 16st 9lb (233lbs) by the year 2000. I was practically immobile and found it hard to move around. I remember waking up one morning and trying to sit up in bed and it was so hard. Getting out of bed was such an effort.
"Then when I walked around the bed, Dawn just watched me and noticed that I was becoming a little immobile. And she said, 'Do you want to go to the doctor? It might be worthwhile finding out why you are getting so heavy.' Of course, she knew why, I was b***dy eating!"
The 'Greatest Day' singer says he felt he had "failed" himself because he had let his weight get out of control.
Gary Barlow added to Britain's OK! magazine: "I look back at pictures of me when I was heavier and it's like being in your own prison. And it's true, and the bigger you are the smaller you feel. You become embarrassed about it. You're meant to look after yourself and I failed because I looked like that."