High levels of obesity in the Midlands, Wales, North East and parts of the South East are shown on a new "fat map" of the UK.
Drawing on data from GPs, the survey by Dr Foster Research shows that more than one in 10 patients in some parts of the country are dangerously overweight.
The highest proportion are found in the Shetland Isles, where 15.5% of patients are obese, followed by many parts of Wales.
Other "fat pockets" include the Bexley Care Trust in London, where 9.1% of patients are obese, Barking and Dagenham primary care trust (9.3%) and Medway PCT in Kent (9.4%).
The North East has a similar problem, including Wakefield District PCT (9.3%), Doncaster PCT (10.1%) and Barnsley PCT (10.8%).
The map was drawn up complied using data from GPs relating to the quality and outcomes framework (QOF) for 2006/07, which keeps a register of patients aged 16 and over with a body mass index of 30 or over in the previous 15 months.
Alex Young, senior project manager at Dr Foster Research, said: "We need to wait a few more years before we can say definitely that things are getting worse but there does seem to be a growing problem in some areas."