I was impressed by Teichholz's ability to cover a huge amount of research spanning many decades and to discuss it critically but fairly without sacrificing readability. Even readers with no scientific background should have no difficulty following the arguments, but that doesn't mean that they are not given enough information to form an opinion. This is popular science of high quality— unlike, Teicholz believes, the dietary advice that has been fed (literally) to millions of Americans and others for years.
We all know what we are supposed to eat and not eat, of course. Restrict fat, and especially saturated fat; cut down on meat, especially red meat; eat lots of grains, fruit and vegetables. This advice hasn't done much to slow the trend to obesity but we are assured that it's the best way to reduce our risk of a heart attack or stroke. Who says so? All the experts (well, nearly all; there have always been a few dissenters but it was difficult for them to get a hearing).
What you may not be aware of is how strongly this advice has been shaped by commercial interests and by politics, both scientific and national. You may also not realise how insecurely founded is the official advice. "It's possible to think of the low-fat, near-vegetarian diet of the past half-century as an uncontrolled experiment on the entire American population, significantly altering our traditional diet with unintended results." And not just the American population, of course.
An important reason why much of the evidence is weak is that it is epidemiological, based on surveys of populations and their diets. Such studies are subject to many uncertainties and, at best, can show only associations not causation. To show causation clinical trials are needed. They were comparatively late to appear, and when they were eventually done they failed to show that following the official dietary recommendations produced the expected reduction in heart attacks and strokes.
For much of the second half of the twentieth century the dominant figure responsible for the establishment of the diet–heart hypothesis as orthodoxy was that of Ancel Keys, whose name will already be familiar to readers of Taubes's book. Teicholz finds his influence to have been wholly pernicious.
To a surprising degree, … the story of nutritional science is not, as we would expect, the story of sober-minded researchers moving with judicious steps. It falls, instead, under the "Great Man" theory of history, whereby strong personalities steer events using their own personal charisma, intelligence, wisdom or wits. In the history of nutrition, Ancel Keys was, by far. the Greatest Man.
The recommended diet was pretty bland and uninteresting. An attractive variant began to be publicised in the 1990s: the "Mediterranean Diet". This advocated poultry, fish, fruit, vegetables, and grains, and also made a virtue of adding olive oil pretty liberally to food. It was strongly promoted by skilled publicists funded in part by the olive oil industry. It was soon being advocated by American nutritionists, well in advance of any scientific evidence to show that it was actually beneficial. In any case, it proved difficult to establish exactly what the Mediterranean diet really consisted of, nor is it clear that the use of olive oil as food in the region is as long-standing or traditional as is claimed. Teicholz concludes that the current enthusiasm for this diet is largely the result of astute marketing. But at least it has moderated Americans' extreme phobia of fat in all its forms.*
Teichholz has a detailed, and alarming, account of how the process of hydrogenation, used to make vegetable oils solid at room temperature, gave rise to the potentially dangerous trans fats. The industry did all it could to resist the research evidence but now these altered fats are being eliminated. Unfortunately, it seems that the oils that are being used to replace them may be equally or even more dangerous, especially when heated.
Like Taubes, Teicholz reaches the conclusion that the late Robert Atkins was on the right lines with his low-carbohydrate diet. In particular, we should have no fear of fat, including saturated fat.
Animal fats were originally condemned on the basis of their ability to raise total cholesterol, and later LDL-cholesterol, both biomarkers that turned out to be unreliable predictors of heart attack risk for the great majority of people. The other evidence against saturated fats involved a handful of early, influential clinical trials that were found not to live up to their original claims. In the end, the case against saturated fats has collapsed.Whether you agree with this conclusion or not, after reading this book you will have a lot of evidence on which to base your opinion.
*The most important trial that seemed to validate the Mediterranean diet was retracted and republished in 2018.