Some writers are ignoring fact that heart health has improved since people moved away from saturated fat.

'Eat butter. Scientists labelled fat the enemy. Why they were wrong" was the headline on a Time magazine cover last year. Journalist Nina Teicholz has written a book titled The Big Fat Surprise: Why Butter, Meat and Cheese Belong in a Healthy Diet.

Teicholz believes she is better able to interpret the scientific evidence than the scientists who did the research because they are either too arrogant to accept they were wrong or too conflicted because their research funds come from "big sugar".

Like numerous books by Gary Taubes, it's full of conspiracy theories and lots of studies contradicting the considered wisdom that saturated fat is a major cause of heart disease. With about 5000 papers published in biomedical literature every day it's not too hard to find plenty of studies to fit their pro-saturated fat theory.

Every scientific study has flaws and Teicholz finds weaknesses in every study supporting the saturated fat-heart disease link, but surprisingly, not in the studies that don't.

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Unlike the scientists, Teicholz tells us she has no conflicts of interest, although a book entitled Shock, Horror, the Scientists were Right - Saturated Fat is an Important Cause of Heart Disease wouldn't sell many copies.

However, in addition to mixing up good and bad fats, every one of these books and articles glosses over or ignores one big, fat embarrassing fact. Heart disease rates have been plummeting across the developed world, with the greatest declines in countries like New Zealand - countries where saturated fat consumption used to be among the world's highest but has plummeted after people switched from butter, full cream milk and dripping to margarine, low-fat milks and vegetable oils, and from fatty red meat to lean red meat and chicken.

Heart disease death rates have fallen by 90 per cent in New Zealand since 1967 with no increase in death rates from other causes. In fact New Zealanders are gaining an unprecedented six hours of life expectancy every day, most of which is due to declining heart disease rates, and most of which is increased healthy life expectancy.

About two-thirds of the decline has been shown to be due to disease prevention rather than better treatment of people with disease. The rate of decline has been similar in men and women, yet declining smoking rates happened much later in women, suggesting that much of the early decline, when we made the greatest dietary changes, is unlikely to have been due to reductions in smoking.

Numerous studies suggest up to one third of this almost unbelievable decline in heart disease has been due to reductions in saturated fat consumption.

Yet if you believed even half of what Teicholz and others have written, we should be dropping like flies.

It is true we are getting fatter and the prevalence of diabetes is increasing and these are serious problems with serious consequences, but they are not caused by a lack of saturated fat. Obesity and diabetes are different diseases with different causes from coronary heart disease, a fact Teicholz and others either don't understand or choose to ignore.

Readers should be cautious about the theories of a self-proclaimed expert like Teicholz who, in her book, manages just one vague sentence acknowledging that heart disease is declining.

She seriously downplays this embarrassing fact and incorrectly suggests it is due to improvements in medical treatment anyway.

New Zealanders and other high-income populations have never lived longer nor been healthier, largely due to reductions in heart disease, stroke and lung cancer.

We now need to tackle obesity and diabetes, but let's not undermine our success in tackling coronary heart disease.

Rod Jackson is professor of epidemiology at the University of Auckland's School of Population Health.