Beachbody’s Insanity program is sold with the promise: “I’ll get you a year’s worth of results in just 60 days!” The Jenny Craig diet promotes that you can: “lose up to 16 pounds in just 4 weeks!” Every globo-gym is running a 45-day weight loss challenge, and most trainers are peddling a variation of the industry’s most effective sales pitch: “in X amount of time with me, you will look like Y.” Whether th