The Great British Bake Off star's dad and granddad both passed away in their 50s.
Lucas, 48, gained weight during the coronavirus lockdowns and said he "was so big I couldn’t really fit on the screen anymore".
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So he decided to make a change and shed the extra pounds.
Opening on the Mid Point podcast, he said: "My dad died when he was 52, very suddenly. His dad died, I think at 56, so I was looking at the law of averages here.
“I was very big and I was getting bigger in the pandemic actually. Sort of not being very active, not really going out, not seeing people, just eating a lot of roast potatoes."
"I was so big I couldn’t really fit on the screen anymore," he added.
The Little Britain star said he cut down on what he was eating and also makes sure he walks a lot.
But he said he's "not skinny by any means" and still has "a proper tummy".
Lucas also shared that when it comes to his clothes, he has gone from an XXL or XXXL to a medium.
He admitted that he feels "relieved" now that he has slimmed down.
Lucas first unveiled his weight loss when he appeared on The One Show earlier this year looking trimmer than usual.
Fans could not get over his transformation and posted messages on social media saying he looked "great".
"That weight loss is amazing," said one, while another said Lucas was "looking fit and fabulous".
"I want to know where the real Matt Lucas went??? I'm positively jealous," joked another fan.
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