I’ve eaten a low-fat diet most of my adult life. I’ve trimmed meat, eschewed butter and cream, and as for ghee, that sultry siren of saturation, I say get behind me, Satan. Sugar, on the other hand, I’ve always believed, is no good for your teeth but otherwise harmless. So if someone had said that what I should have shunned was sugary soft drinks, fruit juices and low-fat smoothies and yogurts, I’d have laughed in their face.

And that’s exactly what US child obesity specialist Robert Lustig is saying, reigniting a seventies debate that he believes went wrong. Lustig’s University of California lecture, now on You-Tube as Sugar: The Bitter Truth, may not be Gangnam Style, but at 3 million plus views, it’s doing better than my lecture on book reviewing. The logic is compelling. We’re eating less fat but we’re getting more fat. We’re living longer but we’re sicker, with increasing rates of obesity, diabetes and the heart disease our low-fat diet is supposed to prevent.

Lustig says a seventies study of seven countries found that those with a high fat diet also had higher rates of heart disease. The study was flawed, he says, along with the logic that since fat leads to cholesterol and cholesterol leads to heart disease, fat must lead to heart disease. One dissenting voice, physiologist and nutritionist John Yudkin, believed they picked the wrong food. Diets high in fat were also high in sugar. Sugar was the bigger problem, according to Yudkin. It was poisonous. Yudkin didn’t change public policy, which went with low-fat, but his ideas are seeing a resurgence and his 1972 book Pure, White and Deadly has just been re-released in the US.

As time went by, we learned oils weren’t oils. There were good and bad cholesterols, the large light HDLs that float around helping us, and dense little LDLs that cause those nasty blockages. Margarine was good then bad. Coconut oil was bad then good. Transfats were very bad. But all through this, low-fat remained the skinny on health.

Lustig believes Yudkin was right. Sucrose (the stuff in sugar bowls)  is made up of equal parts fructose and glucose. Glucose is metabolised in the body’s cells, but fructose, like alcohol and other poisons (hint hint), is metabolised in the liver. The process has a number of nasty by-products, including the LDLs that clog arteries. Fructose suppresses the hormone that tells us we’re full which means we stay hungry and eat more. In terms of weight gain and loss, fructose’s different metabolism means it converts more energy to fat. So a calorie isn’t a calorie, according to Lustig. And if you think you’re okay with an alternative sweetener, honey and agave are full of it. We’re completely fructosed.

Surely sugar’s not bad, I tell myself halfway through Lustig’s lecture (and a chocolate muffin). A little sugar is okay, Lustig admits, especially if you have to chew on a piece of sugar cane to get it, which means you get the fibre needed to deal with the sugar. But we have tonnes of sugar in unnatural form. Check out your low-fat fruit yogurt. Ours has more sugar than fruit. Soft drinks, juices and shop-bought smoothies are all sky-high in sugar, especially with the advent of high-fructose corn syrup, sweeter and cheaper than sugar and ubiquitous in the US where corn agriculture is sweetened with subsidies and sugar is bitter with tariffs.

Lustig’s weight loss program for teens has four simple rules. No drinks except milk and water, eat carbs with fibre, wait 20 minutes for seconds and buy screen time minute-for-minute with physical activity. The program works, he says, but research shows that what makes the difference is sweet drinks.

Not everyone agrees with Lustig. Some say he jumps to conclusions without good evidence. Personally, I like having one thing to blame, especially when there’s an agricultural conspiracy involved, but I also have a sweet tooth. If it turns out I could have smeared my bread with butter and eaten bacon and eggs for brekky and wagyu for lunch every day, maybe I’ll ask for a refund. On the other hand, if it means no more cakes and sweeties and definitely no lashings of ginger beer, I can see why they decided that it was “low-fat” instead of “low-sugar” in the first place.

First published in The Courier-Mail Qweekend  16 March 2013. You can Get in touch with Mary-Rose,  tick the box to receive emails, Like Writer Mary-Rose MacColl on Facebook or follow MaryRoseMacColl on Twitter