Perlmutter in fact dedicates the book to his father, who is in an assisted-living facility across the street from his son’s clinic.

To my father, who at age 96, begins each day by getting dressed to see his patients—despite having retired more than a quarter century ago.

Perlmutter writes about how his father often does not recognize him.

The common defense of writers like Lehrer and Gladwell, and celebrity physicians like Mehmet Oz, is that they make people care to learn about subjects they otherwise would know nothing about. The message may be meretricious, but the end result is a net positive. People might fail to consider their diet entirely if they aren’t told it is destroying their brain. Is this book a problem? What is the worst that can come of avoiding gluten and limiting carbs?

That depends entirely on what you replace those calories with. I read the book with an eye for the most dangerous claim. What stuck out to me was Perlmutter’s case for cholesterol. He basically says that we can’t have too much.

“Nothing could be further from the truth than the myth that if we lower our cholesterol levels, we might have a chance of living longer and healthier lives,” Perlmutter writes. He recommends disowning the notion that LDL is bad cholesterol and HDL is good cholesterol; rather, both are generally good. LDL is only bad when it is oxidized, and it only becomes so in the presence of the sort of oxidative stress brought about by carbs and gluten. Avoid those, and cholesterol is innocuous.

Beyond that, Perlmutter says that cholesterol-lowering statin medicines like Lipitor, which are prescribed for a quarter of Americans over 40, should actually be vehemently avoided. Cholesterol is necessary for the brain in high levels, he says, and lowering it is contributing to dementia.

I took this to Katz, too.

“Is there a weight of evidence that says we can totally ignore both dietary cholesterol and LDL? Absolutely not,” he said. “You can legitimately say we’re starting to rethink some things, but ignoring LDL could absolutely result in heart attacks and strokes. Perlmutter is way ahead of any justifiable conclusion.”

The medical community’s understanding of the danger of cholesterol is changing. Many cardiologists are starting to think that independent of other considerations, the level of LDL in our blood may not be as important as it previously seemed. In November, the American Heart Association and the American College of Cardiology released new guidelines that redefined the use of statins. While they continue to recommend that people at high risk for heart disease and people with LDL levels above 189 take a statin, the long-standing goal of lowering one’s LDL level to 70 is no longer deemed worthwhile to monitor.

Katz acknowledges that dietary cholesterol may be an innocuous part of an overall healthy diet. “The problem is that people are going to get their dietary cholesterol from things other than fish and eggs; they’re going to get it from meats and dairies. The problem with diets like that is if you eat more of A, you’re probably going to eat less of B. So people who are eating more meat and dairy and high-fat, high-cholesterol foods are eating fewer plants—they’re not eating beans; they’re not eating lentils. So yes, I think it’s entirely confabulated and contrived, and potentially dangerous on the level of lethal.”