The 4-hour series borders on sociopathic behavior at times. I'd hardly call it common sense. I think Dwight Garner's review of 4-Hour Body in the New York Times summed up exactly how I felt about 4-Hour Workweek: "“The 4-Hour Body” reads as if The New England Journal of Medicine had been hijacked by the editors of the SkyMall catalog."
Ferris borders on the extravagant when talking about his personal experimentation. He portrays the image of a guy who has tried a million different things to keep the reader from having to. It's extreme, but the actual "advice" is all fairly common sense.
He advocates a slow-carb diet, which has been shown to effectively help people reach a healthy and sustainable weight. He also advocates that people do complex exercises rather than over-focusing on specific muscle groups. That makes up the majority of his health advice, and is not especially controversial and is all fairly common sense. He's basically saying to eat healthy food and to workout regularly if you want to be healthy.
He does throw some stuff in the "love" section that's just meant to sell books, and it's pretty much filler material, but I still wouldn't consider it scammy or bad advice. He's not advocating that people go to extremes like he did.
