Is Sugar Toxic?
By GARY TAUBES
Published: April 13, 2011
On May 26, 2009, Robert Lustig gave a lecture called "Sugar: The Bitter Truth," which was posted on YouTube the following July. Since then, it has been viewed well over 800,000 times, gaining new viewers at a rate of about 50,000 per month, fairly remarkable numbers for a 90-minute discussion of the nuances of fructose biochemistry and human physiology.
Lustig is a specialist on pediatric hormone disorders and the leading expert in childhood obesity at the University of California, San Francisco, School of Medicine, which is one of the best medical schools in the country. He published his first paper on childhood obesity a dozen years ago, and he has been treating patients and doing research on the disorder ever since.
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By the end of the 1970s, any scientist who studied the potentially deleterious effects of sugar in the diet, according to Sheldon Reiser, who did just that at the U.S.D.A.'s Carbohydrate Nutrition Laboratory in Beltsville, Md., and talked about it publicly, was endangering his reputation. "Yudkin was so discredited," Reiser said to me. "He was ridiculed in a way. And anybody else who said something bad about sucrose, they'd say, ‘He's just like Yudkin.' "
What has changed since then, other than Americans getting fatter and more diabetic? It wasn't so much that researchers learned anything particularly new about the effects of sugar or high-fructose corn syrup in the human body. Rather the context of the science changed: physicians and medical authorities came to accept the idea that a condition known as metabolic syndrome is a major, if not the major, risk factor for heart disease and diabetes.
The Centers for Disease Control and Prevention now estimate that some 75 million Americans have metabolic syndrome. For those who have heart attacks, metabolic syndrome will very likely be the reason.
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When physicians assess your risk of heart disease these days, they will take into consideration your LDL cholesterol (the bad kind), but also these symptoms of metabolic syndrome. The idea, according to Scott Grundy, a University of Texas Southwestern Medical Center nutritionist and the chairman of the panel that produced the last edition of the National Cholesterol Education Program guidelines, is that
heart attacks 50 years ago might have been caused by high cholesterol — particularly high LDL cholesterol — but since then we've all gotten fatter and more diabetic, and now it's metabolic syndrome that's the more conspicuous problem.
This raises two obvious questions.
The first is what sets off metabolic syndrome to begin with, which is another way of asking, What causes the initial insulin resistance? There are several hypotheses, but researchers who study the mechanisms of insulin resistance now think that a likely cause is the accumulation of fat in the liver. When studies have been done trying to answer this question in humans, says Varman Samuel, who studies insulin resistance at Yale School of Medicine, the correlation between liver fat and insulin resistance in patients, lean or obese, is "remarkably strong." What it looks like, Samuel says, is that "when you deposit fat in the liver, that's when you become insulin-resistant."
That raises the other obvious question: What causes the liver to accumulate fat in humans? A common assumption is that simply getting fatter leads to a fatty liver, but this does not explain fatty liver in lean people. Some of it could be attributed to genetic predisposition. But harking back to Lustig, there's also the very real possibility that it is caused by sugar.
As it happens, metabolic syndrome and insulin resistance are the reasons that many of the researchers today studying fructose became interested in the subject to begin with. If you want to cause insulin resistance in laboratory rats, says Gerald Reaven, the Stanford University diabetologist who did much of the pioneering work on the subject, feeding them diets that are mostly fructose is an easy way to do it. It's a "very obvious, very dramatic" effect, Reaven says.
By the early 2000s, researchers studying fructose metabolism had established certain findings unambiguously and had well-established biochemical explanations for what was happening. Feed animals enough pure fructose or enough sugar, and their livers convert the fructose into fat — the saturated fatty acid, palmitate, to be precise, that supposedly gives us heart disease when we eat it, by raising LDL cholesterol. The fat accumulates in the liver, and insulin resistance and metabolic syndrome follow.
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When Tappy fed his human subjects the equivalent of the fructose in 8 to 10 cans of Coke or Pepsi a day — a "pretty high dose," he says —– their livers would start to become insulin-resistant, and their triglycerides would go up in just a few days. With lower doses, Tappy says, just as in the animal research, the same effects would appear, but it would take longer, a month or more.
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One of the diseases that increases in incidence with obesity, diabetes and metabolic syndrome is cancer. This is why I said earlier that
insulin resistance may be a fundamental underlying defect in many cancers, as it is in type 2 diabetes and heart disease.
So how does it work? Cancer researchers now consider that the problem with insulin resistance is that it leads us to secrete more insulin, and insulin (as well as a related hormone known as insulin-like growth factor) actually promotes tumor growth.
As it was explained to me by
Craig Thompson, who has done much of this research and is now president of Memorial Sloan-Kettering Cancer Center in New York, the cells of many human cancers come to depend on insulin to provide the fuel (blood sugar) and materials they need to grow and multiply. Insulin and insulin-like growth factor (and related growth factors) also provide the signal, in effect, to do it. The more insulin, the better they do. Some cancers develop mutations that serve the purpose of increasing the influence of insulin on the cell; others take advantage of the elevated insulin levels that are common to metabolic syndrome, obesity and type 2 diabetes. Some do both. Thompson
believes that many pre-cancerous cells would never acquire the mutations that turn them into malignant tumors if they weren't being driven by insulin to take up more and more blood sugar and metabolize it.
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Lewis Cantley, director of the Cancer Center at Beth Israel Deaconess Medical Center at Harvard Medical School, says that up to 80 percent of all human cancers are driven by either mutations or environmental factors that work to enhance or mimic the effect of insulin on the incipient tumor cells.
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If it's sugar that causes insulin resistance, they say, 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. For just this reason,
neither of these men will eat sugar or high-fructose corn syrup, if they can avoid it.
"I have eliminated refined sugar from my diet and eat as little as I possibly can," Thompson told me, "because I believe ultimately it's something I can do to decrease my risk of cancer." Cantley put it this way: "
Sugar scares me."
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http://www.nytimes.com/2011/04/17/magazine/mag-17Sugar-t.html?pagewanted=all
