I came to this book with some heavy skepticism. Teicholz launched into picking apart all the studies and pseudo-studies that I've read about, and it made a lot of sense to me. I'm a physicist, and I often tell my bio-major students (who have to take physics to graduate), who complain that physics is too complicated, that they've got it backward. Biological systems are way more complicated than anything we study, and nutrition scientists have the significant handicap of never being able to isolate their variables. It's really hard to do a real, high-statistics long-term study on the effects of diet.
The history in this book is very informative, and I learned a lot about the political aspect of nutrition science. In an effort to stave off heart disease and save lives, a lot of scientific short cuts were taken, results overstated and then enshrined in government recommendations. It looks like the low-fat diet that has been pushed so hard for so long is sitting on shaky scientific foundations.
So what do we really know? Teicholz has a clear thesis: saturated fat is good for you, monounsaturated is okay, polyunsaturated really bad. The opposite message has been pushed for logical but unscientific reasons. But of course, I'm skeptical of the studies that lead to the conclusion that saturated fat is good for you for the same reason I'm skeptical of the other nutrition studies she picked apart in this book. There seem to be a few salient points: saturated fat does not trigger insulin release, it does raise HDL cholesterol, which seems beneficial, and it's more healthy that trans fats and whatever untested synthetic junk big food is replacing trans fats with now. Polyunsaturated fats used for frying may well be dangerous, as she claims, but that doesn't really conflict with the mainstream message that we shouldn't eat fried foods anyway.
I find the actual science sprinkled throughout the book helpful: the chemical structure of the fats, their roles in hormone release, metabolism, and bodily function including the brain and cell membranes. But most of what we know about nutrition now is still based on diet studies, which seem pretty unreliable (precisely because they're so hard to do well). And this book, naturally, is so focused on fats that there isn't much discussion of the roles of vegetables, fruits, etc, so the argument comes off sounding too one-sided. Of course that's okay. No one book can be said to be scientifically valid and also prescribe every aspect of a diet. Teicholz wanted to make a point about saturated fats, and she's made it well. There's just more to the story.
This book is successful in that it has caused me to rethink the standard dietary recommendations we see everywhere and has convinced me that saturated fat is not the unmitigated evil I've been taught it is for the last couple decades. I'm not about to restrict my diet to red meat fried in lard, but I probably will make some gradual changes. And the book made me think differently and more consciously about what I'm eating and why (where my info is coming from), and that's good for us all.