What if eating fat does not make you fat? It is an idea that could turn decades of established thinking on its head.
The US physicist Gary Taubes has lobbed this scientific ''grenade'' in two books he has written about obesity and nutrition. His premise? That the hormone insulin is responsible for obesity, and levels of insulin spike when we eat carbohydrates, leading us to get fat. Eating fat, he says, does not have this effect on insulin and therefore is not the culprit in making people overweight or obese.
The idea that people are fat because they eat too much says nothing meaningful about why excess calories get stored as fat, says Taubes, who studied applied physics at Harvard. He argues that carbohydrates, such as fructose, corn, potatoes, rice and grains, affect insulin, a powerful regulator of fat. Fat is readily stored in the presence of insulin because it causes the enzyme lipoprotein lipase to suck fat inside cells where it is stored. The body only makes insulin when blood sugar levels rise, and all carbohydrates are metabolised as sugar.
Thus, if we do not eat carbohydrates, there will not be excess sugar in the blood, the body will not make insulin and fat will not be stored by cells, Taubes believes.
Meats, fish, eggs, butter and oil contain few, if any, carbohydrates and do not cause insulin levels to spike, which Taubes says means people can eat as much of those foods as they want so long as they also avoid carbohydrates.
''So this idea all calories are created equal; well, in terms of the energy in the calories, yes … but in terms of the fate of the nutrient downstream, the same amount of calories of different nutrients will have a dramatically different effect,'' Taubes says.
It is a bold stance to take amid the present epidemic of obesity and diabetes, with Australian public health guidelines staunchly placing the blame on eating too much and not exercising enough.
While his ideas are controversial, they are not completely new. Robert Atkins's revolutionary Atkins diet in the 1970s had similar ideas, and low-GI diets also follow some of these principles. But Taubes goes deeply into the science behind the high-fat diet, picks apart studies by major universities more rigorously and is doing so at a time when consumers are frustrated by their inability to lose weight no matter which diets they follow.
Taubes is keen for his work to be digested by health experts clamouring to find some solution to the growing obesity epidemic that is threatening to swamp health systems around the world.
Even Australian nutritionists who view Taubes as a conspiracy theorist because of his criticisms of those who pioneered the idea that fat causes obesity, admit his research has enough credibility and science behind it to be considered.
Whether you believe fat is to blame for rising obesity or not, it is clear the problem is getting worse.
More low-fat foods are being produced and consumed than ever before. Red meat consumption is also declining, with beef consumed in the Australian market decreasing by 3 per cent in 2010-11. Yet, obesity rates in Australia are still climbing.
Taubes says it was when gluttony and sloth became demonised as causes of obesity in the 1960s, that the field of nutrition lost its way while waistlines continued to grow.
''Pre-World War II, all of the best science was done in Europe where there was a culture of excellence in physics, biology and medicine,'' he says.
''Obesity was nothing about eating too much or exercising too little, rather researchers said obesity was a hormonal, regulatory defect just like any other growth disorder. They said there was an excess accumulation of fat occurring, fat is regulated, and so therefore something was wrong with that regulatory system in fat people.
''Then the war came, these researchers disappeared, and so did their accepted theory of obesity.''
In his books, Good Calories, Bad Calories and Why We Get Fat, Taubes writes that a small but influential contingent of American nutritionists - Jean Mayer, Fred Stare, Jules Hirsch, George Bray, Theodore Vanitallie, Albert Stunkard, George Cahill and Philip White - then became the leading authorities in the field. ''They all came out of the north-eastern academic corridor - Harvard, Yale, Columbia, Rockerfeller, the University of Pennsylvania - and they all knew each other,'' he writes.
''None of these authorities actually specialised in the clinical treatment of obesity [except for one], who did so as a psychiatrist treating an eating disorder. Nor were they necessarily the best scientists in their field.''
In the late '70s, Taubes says, these researchers addressed a committee charged with establishing the ''Dietary Goals for Americans'', embracing the committee's recommendation of a national diet lower in fat and higher in carbohydrates.
This was despite one of the scientists, Van Itallie, admitting to the committee that he was unaware of any research conclusively supporting the low fat, high carbohydrate theory of weight loss.
''Thus, what I am saying is an assumption rather than a statement of established fact,'' he told them.
Despite this, the new guidelines were released, and nutritionists and public health authorities latched on to two ideas - that dietary fat causes heart disease and obesity is an energy imbalance between calories in and out, Taubes says.
''The existence of these hypotheses seemed to be reason enough to believe they were true,'' he says.
''We ignored everything that had been learnt about causes of obesity until then and ran with it.''
Taubes has been reporting on controversial science since the early 1980s. First, he wrote a book challenging the theory of cold fusion, a hypothetical type of nuclear reaction. In the 1990s, his focus turned to public health and medical issues, as he believed nutrition was one of the most glaring examples of pseudoscience at play. As low-fat eating became the order of the day, food manufacturers replaced fat in foods with sugar, and as fat consumption declined, Taubes says, obesity, diabetes and the incidence of heart disease kept increasing. He interviewed more than 600 clinicians and investigators in the US and studied peer-reviewed nutrition research from leading medical journals and universities to find out why.
Taubes gained attention when New York Times Magazine published one of his articles in 2002, in which he questioned low-fat diets and promoted a similar way of eating as the Atkins diet before it. He says that diet gained so much controversy because it was introduced when fat had become an accepted culprit by the medical establishment.
While Taubes does not dispute that expending more calories than consumed will lead to weight loss, he argues that method is largely unsustainable, unnecessary and not the most efficient way to prevent fat from being stored by cells.
There are studies that support Taubes's theory, including one from Stanford University published by the Journal of the American Medical Association in 2007, which monitored 77 women for a year. Women placed on a low-carbohydrate, high-fat diet lost more weight than those who ate a diet based on US government guidelines that promote a diet lower in fat and higher in carbohydrates.
Another criticism of Atkins and low-carbohydrate diets is that studies have indicated red meat consumption is associated with heart disease. A Harvard University study published this year found eating a portion of processed red meat daily boosted the risk of dying young by up to 20 per cent.
It is another area of nutrition science challenged by Taubes, who says red meat consumption has only been found as being associated with heart disease and early death, not as a cause of it. On his blog, Taubes wrote: ''Moreover, this meat-eating association with disease is a tiny association. Tiny. It's not the 20-fold increased risk of lung cancer that pack-a-day smokers have compared to non-smokers. It's a 0.2-fold increased risk.''
Taubes used himself to prove his point, for several months eating three eggs with cheese, bacon and sausage for breakfast every morning, a couple of bunless cheeseburgers or a roast chicken for lunch and steak for dinner, and cooking with butter. His blood test results before and after this ''diet'' were posted on his website. They showed after his meat binge, his cholesterol and glucose levels were well within the normal range and had actually improved.
In his books, Taubes refers to studies from the 19th and early 20th centuries where people from very poor populations, who ate little aside from bread and corn, also displayed moderate to high levels of obesity. But these studies have fallen by the wayside, he says, partly because the low-fat dogma has become so enshrined in medical thinking.
''The medical community believes it's an energy balance problem and people powerfully believe that,'' Taubes says. ''If you spend your whole career thinking obesity is about eating too much, it's very hard to turn around and say, 'I was wrong'. Imagine the public health authorities in the US and Australia saying 'Look, we were wrong, we're sorry, maybe we killed some your loved ones but eventually we got it right'.
''It doesn't help their credibility.''
Professor Tim Gill, from Sydney University's Boden institute of obesity, nutrition, exercise and eating disorders, describes Taubes as a respected science writer who is well researched but divisive.
A growing number of academics and clinicians support his research, Gill says, but he believes Taubes, who also has a masters in journalism from Columbia University, has not done enough to prove that public health guidelines should be overhauled just yet.
''Journalists love to come up with something that is the antithesis of what's currently held by academics because they like to believe in a conspiracy,'' Gill says.
''He's come up with an idea, which is perfectly rational to a point, which some academics agree with, but he can be as selective as anyone else in the evidence he uses to support his own arguments.''
Gill admits researchers interested in nutrition have generally been guilty of being too simplistic in the past, by focusing on one aspect, such as fat.
But by only criminalising carbohydrates, he believes Taubes has ignored many other elements of weight gain as well.
''The causes of obesity and weight gain are much more complex than just carbohydrates,'' Gill says.
''Whilst we were happy in the past to accept one or two big studies from big names and go along with it, all research has its problems and its limitations. And despite all this evidence we have, we still really don't have absolute clarity around certain aspects of nutrition.''
Even Taubes acknowledges his theory of obesity needs more research.
In September, he launched the non-profit Nutrition Science Initiative in San Diego, which describes its purpose as to ''facilitate and fund rigorous, well-controlled experiments targeted at resolving unambiguously many of the outstanding nutrition controversies - to answer the question definitively of what constitutes a healthy diet and dedicated to dramatically reducing the economic and social burden of obesity and obesity-related diseases."
Led by Taubes, the initiative will carry out highly controlled experiments headed by researchers from around the US - including those sceptical of the carbohydrate hypotheses Taubes hopes to test.