Today 65% of U.S. adults are classified as overweight, up from 46% two decades ago. And nearly a third of adults are considered obese, up from 14% in 1980. Any way you look at it, heavy Americans represent a fast-growing market with special needs. Until recently the business world's primary response was to pitch diets, workouts and potions to those determined to melt off the pounds. The weight-loss market grew to about $40 billion last year, from $33 billion in 1999. Even drastic measures are catching on.