Thyroid conditions account for maybe 10-15 lbs of weight gain, and can be medically treated after diagnosis from a competent medical professional.
Thighroid condishuns, on the other hand, result in 100-150+ lbs of weight gain, are "impossible" to treat, and are 100% self-diagnosed.
Every time I hear someone say they have a thyroid condition and that's why they're heavy, I ask what medication they're on. They never are, because they've never actually been diagnosed with a thyroid condition. (Google "fat logic")
As a formerly obese person myself (and still about 6 lbs to go before I hit "normal" weight... *sigh*), just about any (especially obese people) *can* lose weight, just by changing what they eat. And by that, I mean what they *actually* eat, not their claim of "1 small salad then starve myself for the rest of the day while working out 4 hours at the gym every day".
As an aside, the reference Simpsons episode, "King-Size Homer", has Homer gaining enough weight, in 1995, to be considered disable at *300 lbs*. Today, that's pretty much a commonplace weight in today's world. Think about that... A 239 lb Homer is "fat", and a 300 lb Homer is now "disabled", yet a good chunk of the population is already at or above those weights...