New figures released by Trust for America’s Health paint an increasingly fat picture of the U.S. Twenty years ago, not a single state in the union had an obesity rate higher than 15 percent; today, only Colorado is below 20. With increased obesity comes a commensurate increase in related illnesses like diabetes, heart disease, hypertension, and many forms of cancer. By now, everyone knows that dietary carbohydrates, not fats, are what cause weight gain. (Well, almost everyone, except food industry-bullied groups like the USDA.) But a twist is developing in our understanding of many obesity-related illnesses: A growing body of evidence points to sugar as the true cause of many obesity-related diseases.


Sugar is not just empty calories, it’s poison, argued Dr. Robert Lustig in his 2009 lecture-turned-YouTube “Sugar, the Bitter Truth.” He’s a specialist in pediatric disorders at UC-San Francisco. His 90-minute lecture has been viewed more than 1 million times. Critics argue that he’s being overly dramatic, but if what he’s saying is true, it would be tricky to present it dramatically enough.


The rise of obesity correlates with efforts in the early 1980s by the AMA, USDA, and American Heart Association to decrease our fat intake. As Lustig and others have pointed out, food producers responded by adding sugar to make processed fat-free foods more palatable. Added sugar has become so widespread that many baby formulas now contain as much as Coca-Cola. And even before their first taste of formula, many babies have already developed a taste for sugar. Research has shown that early exposure to sugar, including in-utero exposure, encourages a lifelong sweet tooth.


Lustig’s thesis, in a nutshell, is that sugar stimulates fat accumulation in the liver, which leads to insulin resistance, which causes the body to create more insulin. High insulin causes diabetes and has been linked to hypertension. And insulin promotes tumor growth, including cancers of the colon and breast.


Sugar comes in many forms, but fructose is the culprit, Lustig says. A molecule of common table sugar, aka sucrose, is composed of one molecule each of glucose and fructose. Glucose is an essential nutrient that the body manufactures if dietary sources aren’t sufficient. Fructose, on the other hand, goes straight to the liver, the only place in the body where it can be metabolized. There it’s converted to palmitate, a type of fat that’s been shown to cause heart disease in humans when ingested.


Researchers have found a strong correlation between palmitate and high insulin in humans – including non-obese humans. Studies on rats, meanwhile, have demonstrated that a fructose-heavy diet will give them high insulin. If the fructose diet stops, the high insulin goes away.


Until recently, most researchers looking at links between cancer and insulin have operated on the assumption that high insulin is a consequence of being fat and under-active, according to nutrition writer Gary Taubes in an April 13 article in The New York Times Magazine. He says he finds Lustig’s argument – that fructose is the real cause of obesity-related diseases – compelling.


“If it’s sugar that causes insulin resistance, then the conclusion is hard to avoid that sugar causes cancer – some cancers, at least – radical as this may seem and despite the fact that this suggestion has rarely if ever been voiced,” he writes. 


But proving this link in humans is complicated by pesky ethical issues – namely, that we can’t go around giving high doses of fructose to people to see if it gives them cancer. Hence the sugar and corn syrup industries (and their Most Valuable Puppet, the USDA) argue that the evidence implicating fructose is inconclusive, saying, tobacco industry-style, that “more research is necessary.”


Clearly, more research is necessary. Even if links between fructose and disease are proven, what constitutes a safe amount of fructose should be established.


Like sucrose, corn syrup is a mix of glucose and fructose, the most common ratio being 45 to 55 percent. This makes corn syrup, in terms of fructose content, only marginally worse than straight table sugar. And while many people have no problem demonizing corn syrup, fresh fruit – another fructose-rich food – is more problematic to implicate. After all, isn’t fruit the epitome of healthy food?


Lustig isn’t going there, saying fruit contains fiber, which counteracts many negative effects of fructose. Fiber inhibits the absorption of fructose in the small intestine, allowing intestinal flora to digest it before the liver, causing farting rather than fattening. And fiber reduces hunger, making it hard to gorge on fruit.


Today’s big, juicy, sweet fruits, products of ag breeding, were not available during prehistoric times. Smaller, less sweet fruit were available, and only for a few months. The fact that the effects of fructose binging can be reversed by removing fructose dovetails nicely (if circumstantially) with the idea our ancestors evolved to be seasonal eaters.


Processed carbohydrates like pasta are broken down to glucose in the body, which means they aren’t a source of fructose. Those carbohydrates will make you fat if you’re not careful. But they won’t make you sick. It’s looking more and more like sugar will make you both.