The BMI tables are here:
http://www.bcbst.com/MPManual/HW.htm
Health insurers start calculating an extra premium for overweight after about a BMI of 20; anybody of BMI 25 (e.g. a 5 ft 9 in woman weighing 170 lbs) is not only statistically fat, she's borderline obese. Exceptions are made for athletes, because muscle weighs more than fat:
"A person can be overweight without being obese, as in the example of a bodybuilder or other athlete who has a lot of muscle."
http://win.niddk.nih.gov/statistics/
A recent study in The Lancet confirmed that obesity is linked with twice the risk of death or severe illness as smoking a pack a day for decades - which accounts for the fact smokers are the most profitable population for insurers, since they have to pay extra premiums in spite of being generally thin, while the obese are individually uninsurable by private industry.
To cheer everybody up, here's an article about the Lancet study in the London Times:
"Evidence that secondary smoking harms health is as scientific as a Ouija board. But that has not prevented it boosting hostility to cigarettes from opinion to legislation. Now government must urgently demonstrate the dangers of secondary fattening.
A threat exists every time I see some svelte young thing consuming chips and imagine that it may be safe for me to eat them too. Such public displays must be outlawed. "
http://www.timesonline.co.uk/article/0,,3284-1654311,00.html