Is Sugar a Poison?

[Ed Note: This is part one of a two part investigation into contemporary thinking on sugar.  Today’s post focuses on recent discussions while part two will provide Linus Pauling’s perspective as well as that of an important contemporary.]

After watching Robert Lustig’s lecture “Sugar: The Bitter Truth,” posted on YouTube in July 2009, viewers are sure to sympathize more with their livers, and with Lustig’s persuasive evidence that sugar is a toxin. Robert H. Lustig, M.D., is a professor of Pediatrics in the Division of Endocrinology at the University of California, San Francisco, School of Medicine, who, over the course of a 90-minute discussion on fructose, glucose and the body’s reaction to them, aims to convince the public that sugar is not just bad for us, it is toxic.

Lustig begins his engaging lecture by arguing that the reason why Americans are getting fatter is because our bodies aren’t telling us when we’re full. The hormone leptin, which signals satiety, must be malfunctioning, he says, because now we’re just eating more food. It is true that portion sizes used to be smaller, he admits, but food was just as available twenty years ago as it is now. Fat isn’t the culprit either, because we eat fewer calories from fat now than we did in the 1980s, yet obesity is still rising.

One component of the problem is what Lustig calls the “Coca-Cola Conspiracy”: Coca-Cola has become saltier, which makes you thirsty, but the salt is masked by added sugar, so the taste buds do not detect extra salt. Likewise, more caffeine has been added, providing energy but also working as a diuretic.  As a result of the added caffeine and salt, you are actually thirstier when you finish the Coca-Cola than when you started it, making you want more Coca-Cola. In the process, of course, you consume more sugar.

Robert Lustig being inteviewed by ABC News correspondent John Donvan. Credit: UC-San Francisco.

Sugar is bad, but the main crux of Lustig’s argument is that fructose in particular is a poison. Sucrose, or table sugar, is made up of 50 percent fructose and 50 percent glucose; the glucose is metabolized by every cell in the body, while the fructose is metabolized solely by the liver. High-fructose corn syrup, or H.F.C.S., is made up of 55 percent fructose and 45 percent glucose. Lustig, however, makes no distinction between sucrose and H.F.C.S., saying that both should be included in the discussion about sugar since both are processed by the body the same way.

According to Lustig, President Richard Nixon’s 1973 campaign to decrease the price of food is partly to blame for spurring the advent and popularity of H.F.C.S.  For one, H.F.C.S. is both cheaper and sweeter than sucrose, so manufacturers eventually used it more than sugar, advertising it as the healthy, natural alternative. What added to the problem, Lustig says, was the campaign by the U.S. Department of Agriculture, the American Medical Association and the American Heart Association in 1972 to cut down on fat in the American diet. This effectively diminished the amounts of fat that we ate, but did not solve the problem: “The fat’s going down, the sugar’s going up, and we’re all getting sick.” In Lustig’s view, it became apparent rather quickly that a low-fat, high-carb diet tasted like “crap,” so sugar was added to make it more palatable to the consumer’s tastebuds.

Lustig spends about fifteen minutes of his presentation giving a biochemistry lesson demonstrating that glucose and fructose are not the same thing, and also showing all the adverse physiological effects of fructose. From there, he returns to the claim made at the beginning of his lecture, which is that Americans are gaining weight because we don’t feel full. The problem with fructose, says Lustig, is that it does not stimulate insulin, and if the insulin levels do not rise, leptin is not activated, thus your brain does not receive the message that you are full. On the contrary, thanks to the unresponsiveness of the insulin, the brain receives the message that the body is starving.

Adding to the “evil” of fructose is its similarity to ethanol. Ethanol is just fermented sugar, and fructose is “ethanol without the buzz,” as Lustig puts it. The only difference, according to Lustig, is that ethanol is metabolized by the brain, causing central nervous system depression, hypothermia, hypoglycemia and loss of fine motor control, to name a few adverse effects. Fructose, on the other hand, is not metabolized by the brain at all. Further, ethanol is regulated by the government because it is considered a toxin, while sugar is not seen as dangerous. Yet, according to Lustig, chronic sugar exposure causes conditions such as hypertension, myocardial infarction, obesity, fetal insulin resistance and other assorted health problems. Fructose and ethanol are metabolized the same way by the body, but it is chronic exposure to fructose that leads to adverse effects, while with ethanol, the effects are more immediately apparent.

So what is the solution to obesity? Lustig, who treats obese children, prescribes four aspects of “lifestyle intervention” that work: a diet containing carbohydrates with fiber; no sugared beverages; following the “Paleolithic diet,” which contains mostly raw foods and no grains; and exercise.

Journalist Gary Taubes provides more insight on Lustig’s lecture in his New York Times article “Is Sugar Toxic?” published on April 13, 2011. Taubes has spent much of the last decade conducting journalistic research on diet and chronic diseases, and agrees with Lustig, noting, “[i]f I didn’t buy this argument myself, I wouldn’t be writing about it here.” Taubes agrees with Lustig that the problem with sugar lies not with the calories that it contains, but with the way our bodies metabolize the fructose.

According to Taubes, in an experiment involving laboratory rats and mice, it was found that if enough fructose hit the liver quickly enough, the liver would convert most of it to fat. He reiterates Lustig’s conclusion that this process eventually results in insulin resistance, which is the fundamental problem in obesity and the underlying defect in heart disease and Type 2 diabetes. However, Taubes says, the Institute of Medicine published a report in 2005 which “acknowledged that plenty of evidence suggested that sugar could increase the risk of heart disease and diabetes…but did not consider the research to be definitive. There was enough ambiguity…that they couldn’t even set an upper limit on how much sugar constitutes too much.”

Gary Taubes

Taubes next discusses the correlation between sugar consumption and diabetes: in 1980, roughly one in seven Americans was obese while almost six million were diabetic. By the early 2000s, a third of Americans were obese, while fourteen million were diabetic. On the basis of this evidence, Taubes says, it is easy to blame the over-consumption of sucrose and H.F.C.S. for the increase in health problems, since peak times of sugar consumption often correlate with spikes in obesity and diabetes.

Sugar is also likely to cause heart disease, although Taubes acknowledges that it is usually dietary fat that is blamed. He notes that in most cases where evidence was presented that indicated dietary fat was a culprit in heart disease, sugar was ignored, even though sugar consumption could also have been a factor. For example, in the 1960s Elliott Joslin, a leading authority on diabetes, claimed that sugar did not cause diabetes because the Japanese ate lots of rice, which is mostly a carbohydrate, like sugar, and there are very few diabetics in Japan. However, he did not take into account that the Japanese also ate much less table sugar than did Americans and, as Taubes brings to our attention, he did not know that rice and sugar are metabolized differently by the body.

Taubes comments that the last time an academic claimed that sugar was a toxin was in the 1970s, when John Yudkin, an authority on nutrition in the United Kingdom and a colleague of Linus Pauling, published a book about sugar called Sweet and Dangerous. In it, Yudkin recounts a series of experiments that he conducted in which sugar and starch were fed to rodents, chickens, rabbits, pigs and college students. The trials found that sugar raised the blood levels of triglycerides, which is a risk factor for heart disease. Sugar also raised insulin levels, linking it to type 2 diabetes.

At the time Yudkin’s conclusions were criticized and his work was not taken seriously. By extension, other researchers who disparaged sucrose were often compared to Yudkin and dismissed. However, according to Taubes, in recent years “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.” Metabolic syndrome is a state in which the cells in one’s body actively ignore insulin, which happens when the pancreas becomes exhausted from pumping out insulin in response to rising blood sugar levels; in some cases, rising blood sugar levels result in diabetes. Other results of chronically elevated insulin levels are heart disease, higher triglyceride levels and blood pressure, and lower levels of HDL cholesterol, which makes the insulin resistance worse. This cycle is known as metabolic syndrome.

So, Taubes asks, what causes the initial insulin resistance? His answer is that “researchers who study the mechanisms of insulin resistance now think that a likely cause is the accumulation of fat in the liver.” Fatty livers are caused by genetic disposition, eating fatty foods, and by consuming fructose, since the liver converts fructose directly to fat if it is hit with a large amount all at once. Fructose is a “chronic toxin,” meaning that it is “not toxic after one meal, but after 1,000 meals.” As a result, conclusive evidence linking fructose to fatty livers will not be forthcoming until long-term studies are conducted.  And, according to Taubes, at this point no studies have been planned that span longer amounts of time.

Finally, Taubes discusses cancer’s link to metabolic syndrome and diabetes, saying, “you are more likely to get cancer if you’re obese or diabetic than if you’re not, and you’re more likely to get cancer if you have metabolic syndrome than if you don’t.” Both metabolic syndrome and diabetes are linked to the Western diet, and countries that do not follow the Western diet experience much lower rates of cancer. One population cited by Taubes are the Inuit in the Arctic, among whom breast cancer rates were almost non-existent until the 1980s. The connection given by cancer researches, Taubes says, is that insulin resistance leads to the secretion of more insulin, and insulin promotes tumor growth.

Taubes ends his article with the statement, “Sugar scares me…I’d like to eat it in moderation. I’d certainly like my two sons to be able to eat it in moderation, to not overconsume it, but I don’t actually know what that means, and I’ve been reporting on this subject and studying it for more than a decade.” Together, Lustig and Taubes paint a dreary picture of the world’s health if it continues to consume fructose: obesity, diabetes, heart disease, and metabolic syndrome are the tangible consequences of the Western lifestyle, with Lustig’s explanation and Taubes’s analysis backing the claim that sugar is toxic.


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