The Big Fat Surprise: Why Butter, Meat and Cheese Belong in a Healthy Diet. By Nina Teicholz. Simon & Schuster; 479 pages; $27.99. Buy from Amazon.com, Amazon.co.uk

“EATING foods that contain saturated fats raises the level of cholesterol in your blood,” according to the American Heart Association (AHA). “High levels of blood cholesterol increase your risk of heart disease and stroke.” So goes the warning from the AHA, the supposed authority on the subject. Governments and doctors wag their fingers to this tune the world over. Gobble too much bacon and butter and you may well die young. But what if that were wrong?

Nina Teicholz, an American journalist, makes just that argument in her compelling new book, “The Big Fat Surprise”. The debate is not confined to nutritionists. Warnings about fat have changed how food companies do business, what people eat, and how and how long they live. Heart disease is the top cause of death not just in America, but around the world. The question is whether saturated fat is truly to blame. Ms Teicholz’s book is a gripping read for anyone who has ever tried to eat healthily.

The case against fat would seem simple. Fat contains more calories, per gram, than do carbohydrates. Eating saturated fat raises cholesterol levels, which in turn is thought to bring on cardiovascular problems. Ms Teicholz dissects this argument slowly. Her book, which includes well over 100 pages of notes and citations, covers decades of nutrition research, including careful explorations of academics’ methodology. This is not an obvious page-turner. But it is.

Ms Teicholz describes the early academics who demonised fat and those who have kept up the crusade. Top among them was Ancel Keys, a professor at the University of Minnesota, whose work landed him on the cover of Time magazine in 1961. He provided an answer to why middle-aged men were dropping dead from heart attacks, as well as a solution: eat less fat. Work by Keys and others propelled the American government’s first set of dietary guidelines, in 1980. Cut back on red meat, whole milk and other sources of saturated fat. The few sceptics of this theory were, for decades, marginalised.

But the vilification of fat, argues Ms Teicholz, does not stand up to closer examination. She pokes holes in famous pieces of research—the Framingham heart study, the Seven Countries study, the Los Angeles Veterans Trial, to name a few—describing methodological problems or overlooked results, until the foundations of this nutritional advice look increasingly shaky.

The opinions of academics and governments, as presented, led to real change. Food companies were happy to replace animal fats with less expensive vegetable oils. They have now begun abolishing trans fats from their food products and replacing them with polyunsaturated vegetable oils that, when heated, may be as harmful. Advice for keeping to a low-fat diet also played directly into food companies’ sweet spot of biscuits, cereals and confectionery; when people eat less fat, they are hungry for something else. Indeed, as recently as 1995 the AHA itself recommended snacks of “low-fat cookies, low-fat crackers…hard candy, gum drops, sugar, syrup, honey” and other carbohydrate-laden foods. Americans consumed nearly 25% more carbohydrates in 2000 than they had in 1971.

In the past decade a growing number of studies have questioned the anti-fat orthodoxy. Ms Teicholz’s book follows the work of Gary Taubes, a science journalist who has cast doubts on the link between saturated fat and health for well over a decade—and been much disparaged for his pains. There is increasing evidence that a bigger culprit is most likely insulin, a hormone; insulin levels rise when one eats carbohydrates. Yet even now, with more attention devoted to the dangers posed by sugar, saturated fat remains maligned. “It seems now that what sustains it,” argues Ms Teicholz, “is not so much science as generations of bias and habit.”