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 percent. With increased obesity comes a commensurate increase in related illnesses such as 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 and the people who inexplicably listen to them. But a twist is developing in our understanding of many obesity-related illnesses: A growing body of evidence points to sugar, rather than being overweight, as the true underlying 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 video "Sugar, the Bitter Truth." Lustig is a specialist in pediatric disorders at the University of California, San Francisco. (His 90-minute lecture has been viewed more than a million times.) Critics argue that he's being overly dramatic, but if what he's saying is true, it would be difficult to present it dramatically enough.
The rise of obesity correlates with efforts in the early 1980s by the American Medical Association, 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 sugar 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—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 is discontinued, 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. Taubes says he finds Lustig's argument—that fructose is the real cause of obesity-related diseases—and the research Lustig's theory is built on, compelling.
"If it's sugar that causes insulin resistance," he writes, "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 before publicly."
But proving this link in humans is complicated by pesky ethical issues. We can't go around giving high doses of fructose to people to see if it gives them cancer. Because of this hurdle, the sugar and corn syrup industries (and their Most Valuable Puppet, the USDA) have been able to argue that the evidence implicating fructose is inconclusive and circumstantial, hiding behind the tobacco industry-style assertion 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. After all, in high enough amounts, broccoli is probably poisonous too.
Like sucrose, corn syrup is a mix of glucose and fructose, the most common ratio being 45 and 55 percent, respectively. 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, an apple a day and all?
Lustig isn't going there, saying that fruit contains fiber, which counteracts many of the negative effects of fructose. For one thing, fiber inhibits the absorption of fructose in the small intestine, allowing intestinal flora to digest it before it reaches the liver, causing farting rather than fattening. And fiber reduces hunger, making it difficult to gorge on fruit.
But fruit juice, even unsweetened, is a different story, Lustig says. He points out that it's a lot easier (and more common) to drink a glass of filtered orange juice than it is to eat the six oranges that went into it.
There are some, like the Paleo crowd, who avoid fruit altogether. Practitioners of the Paleolithic Diet seek to emulate, with varying degrees of fundamentalism, the diet humans ate during our formative development period. Today's big, juicy, sweet fruits, products of agricultural breeding, were not available during Paleolithic times. The fruit that was available in prehistoric times was generally smaller, less sweet, and not available year-round. As mentioned above, the effects of fructose binging can be reversed by removing fructose from the diet—a fact that dovetails nicely, if circumstantially, with the idea that our ancestors evolved to be seasonal fruit eaters.
Processed carbohydrates like pasta are broken down to pure 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 at least they won't make you sick.
It's looking more and more like sugar will make you both.