The majority of people do not realise that their spare tyre or "muffin top" is putting them at increased risk of cancer, heart disease and diabetes, according to a poll.
Excess weight around the middle generates oestrogen and excess chemicals in the stomach, raising the risk of killer diseases.
However, a stunning 97% of people are unaware of a link, even though 71% of those surveyed admitted having a spare tyre.
Women whose waist measures more than 80 cm (31.5 inches) are at risk of type 2 diabetes and heart disease, while men with more than 94 cm (37 inches) are at risk.
The survey of more than 2,000 people was commissioned by Diabetes UK, Cancer Research UK and the British Heart Foundation (BHF), who have come together to launch a new Active Fat campaign to raise awareness of the dangers of excess weight around the middle.
Dr Mike Knapton, Associate Medical Director for the BHF, said: "That 'harmless' spare tyre around your waist is actually a major health hazard. While you might be relaxing at home, your fat cells are working overtime to pump out excess hormones and other chemicals that can cause disease."