There are two common responses to this question, as there will be to the arguments made in this book. One response is to take into account the uncertainties about the health effects of fats and carbohydrates and then suggest that we simply eat in moderation. This in turn implies eating a balanced diet in moderation. “Perhaps our most sensible public health recommendation should be moderation in all things, and moderation in that,” as the University of Michigan professor of public health Marshall Becker suggested back in 1987. But some of us do eat with admirable restraint of the four major food groups and yet are obese or overweight anyway, and presumably have an increased risk of other chronic diseases because of it; some of us are suitably lean, eat balanced diets in moderation, and exercise regularly and yet are insulin-resistant and maybe even diabetic.

The more optimistic response is a compromise position: to take virtually every reasonable hypothesis from the past fifty years that can coexist with the saturated-fat/cholesterol hypothesis of heart disease and fold them all into one seemingly reasonable diet that might do us good and probably won’t do harm. Thus, the current conception of a healthy diet is one that minimizes salt content and maximizes fiber; has plenty of good fats (monounsaturated and omega-three polyunsaturated fats) and minimal bad fats (saturated fats and trans fats); has plenty of olive oil and fish, and little red meat, butter, lard, and dairy products. When meat is consumed, it’s lean, which keeps saturated-fat content down and reduces energy density and thus, supposedly, calories. Dairy is low-fat or no-fat. The diet has plenty of nuts and legumes and good carbohydrates, which are those with copious vitamins, minerals, antioxidants, and fiber (vegetables, fruits, and unrefined grains), but few bad carbohydrates, which are energy-dense and thus contribute to obesity (highly refined carbohydrates and sugars).

It may be true that such a diet is uniquely healthy—but we have no idea if that’s really so. The diet has the advantage of being politically correct; it can be recommended without fear of ostracism from the medical community. Whether it is healthier, however, than, say, a meat diet of 70–80 percent fat calories and absent carbohydrates almost entirely, as Stefansson suggested in the 1920s, or any diet of animal products (meat, fish, fowl, eggs, and cheese) and green vegetables but absent entirely starches, sugar, and flour or even sugar alone, is still anybody’s guess. And whether such a diet would prevent us from fattening or reverse obesity, or do it better than a mostly meat diet, has also never been tested. If it doesn’t, then it’s probably not the healthiest diet, because excessive fat accumulation is certainly associated with increased risk of chronic disease.