He walked on a treadmill for 45 minutes most mornings while watching documentaries and political debates from the US and the UK. The Conservatives leader said it was "easy" to lose the kilograms once he had weaned himself off sugar.
The aspiring politician and businessman now tipped the scales at a gaunt 75kg.
Asked whether he could get any thinner, he said: "My body has naturally levelled out.
"I'm the same weight that I was in my early 20s. I've pretty much got the same physique.
"That's the criteria for me. I'm in that sweet spot, at my perfect BMI. It sets me up for a good year."
Weighty issue
Colin Craig's weight-loss programme
• No sugar
• 45-minute walk, 3 to 4 days a week.
• No alcohol except at social events.