General

www.geographylwc.org.uk/A/AS/AShealth/pdf/GFAQA7.pdf

Apparently statistics suggest that obesity rates are above the national average in Cumbria, South Yorkshire and North East Derbyshire, some places in East Anglia, and the West Midlands. The prevalence of raised waist circumference was greatest in Yorkshire and Humber.

Whether or not it would be good for a BBW to live in those places I don't know. You might find eg. GPs under pressure to reduce the obesity rates and therefore holding more negative attitudes about being overweight.

London is best for the fat social stuff (regular BGPs and FF meets anyway!), but I'm pretty sure it's one of the slimmest cities in general (but it also has the largest population, so statistically maybe you'll have just as good a chance at meeting a fatty!?)