Watson said he was motivated to take better care of his health after reading about Labour politicians who died early.
The 51-year-old revealed one part of his new regime was so-called “bulletproof” coffee – usually made using butter – which is “a way of getting saturated fats into your diet which means you’re not as hungry during the day”.
Watson told ITV’s Peston On Sunday: “I basically stopped taking sugar, refined sugar, and then I started walking 10,000 steps a day and walking up staircases and when a bit more weight came off I started to jog and cycle.”
The West Bromwich East MP, first elected in 2001 said he was the “thinnest I’ve been” since entering the Commons.
He added: “I kept reading about Labour politicians that died early in their 50s and 60s and I want to get healthy, and actually for me the journey’s been very interesting because what I realise is there’s a lot more we can do in public health to deal with the obesity crisis, because you know we’ve got 10 million of these people heading to diabetes, another 15 million sitting behind them are overweight.
“When you read in the papers or you hear political speeches it’s like we condemn them and we judge people who are overweight and I think this is a nutritional issue that retailers, manufacturers, public health officials and politicians have got to take seriously. “