'It wasn't so much about the weight. It was more that I was a fat, lazy, out of shape slob, to be honest,' Gervais told People.
The 49-year-old comedian lost the pounds by running around his London neighbourhood, helping him lose 22lbs.
Gervais says he made no conscious changes to his diet, but got out of the habit of snacking late at night.
'I didn't eat differently. I probably just stopped having that second meal at 11:30 at night.'
Fallon, Gervais's love of more than 25 years, played a key role in helping the Office star slim down, losing 18lbs herself at the same time.
'I think it is because I was trying to lose weight as well,' she said. 'So I was cooking healthier version of what we were eating. He didn't realize that I was probably feeding him less calories at the same time he was running.'
Unfortunately, there's a down side to the new sleeker Gervais.
'Now I've got to stop making jokes about fat people, which is annoying,' he said. 'When I was fat, it was okay.'