A best-selling book about nutrition has a power to influence the national diet that many health professionals can only dream about. And, if David Gillespie’s success is anything to go by, being a layman author is an advantage.

Freed of the constraints and caveats of scientific precision, the layman can use overstatement and simplistic messages to craft a story that resonates with the man or woman in the street.

In Gillespie’s earlier book Sweet Poison, he took the familiar dietary message to limit sugar intake, greatly elevated its health significance and broadcast it. Although the experts pooh-poohed his science, it could be argued that the whole exercise was positive for public health.

The same cannot be said for Gillespie’s latest book Toxic Oil, which carries the subtitle “Why vegetable oil will kill you and how to save yourself”. Here, the author’s key message is diametrically opposed to that of just about every reputable nutrition authority in the world.

At a time when a consensus has emerged that polyunsaturated fats are the preferred replacement for dietary saturated fats for the prevention of coronary heart disease, Gillespie declares that polyunsaturated fats actually increase coronary risk. And, for good measure, they increase the risk for cancer and macular degeneration too. Saturated animal fat is recommended as a healthier choice.

Despite claiming to be “Australia’s No. 1 Health Crusader”, Gillespie has no qualifications in nutrition or any other health science but argues that, as a lawyer, he knows how to assess evidence.

Over the last four years, there has been a lively debate in the scientific literature about saturated fat and its preferred replacement in the diet. Two meta-analyses of randomised controlled trials with clinical end points have been published as well as a pooled analysis of prospective cohort studies, not to mention the scores of studies of the effects of dietary fats on blood lipids in the literature.

Yet none of this found its way into Toxic Oil. Instead, the author re-visits some of the earliest studies into dietary fats and heart disease and revives the cholesterol controversy that those early studies generated 40 years ago.

The arguments presented are not original. Rather, like so many articles found on the internet, they flow from the familiar script of the cholesterol sceptics – Ancel Keys (an early research in the field) fiddled his figures; saturated fat and cholesterol have nothing to do with heart disease; it’s all been a con; and the truth can now be revealed.

The prevarication continues in the section headed Polyunsaturated fats cause cancer, which is supported by minimal evidence – a non-significant finding in a trial commenced in the 1960s and a single prospective cohort study showing a weak association between polyunsaturated fat consumption and increased risk for breast cancer.

Any reasonable review of the evidence on this topic could not have missed the pooled analysis of prospective cohort studies that showed no link. Somehow, the author of Toxic Oil comes to a conclusion at odds with every leading nutrition and cancer authority in the world.

This book will not appeal to the health professional. There’s almost no referencing and some data are presented in figures without acknowledging the source, so they can’t be checked. In one instance, British data are used to support an argument on the grounds that Australian data are “pretty thin on the ground”. Relevant Australian data are readily available; they just don’t support the argument.

Predictably, the dietary recommendations that flow from all this non-evidence leave a lot to be desired. Gillespie sums up his advice better than we can do:

If you do what I suggest, you will be doing all the wrong things, according to our health authorities. You’ll be eating butter, drinking full-fat milk, chomping through bacon and eggs for breakfast and enjoying a meat pie for lunch.

The message is so over-the-top that it’s hard to believe that anyone would take it seriously. Still, messiahs develop followers and the author’s previous advocacy on sugar probably guarantees him an audience that is at least prepared to listen. But any public good that came from David Gillespie’s earlier work will be undone by this poorly researched and ill-conceived book.