Tuesday, July 24, 2012

Should Sugar Be Considered a Poison?

In a previous article, If We Are What We Eat, We Aren’t What We Used To Be: Corn, Nuts, and Sugar, we discussed a number of substances that are being ingested in ways inconsistent with human experience throughout evolution. Sugar is one of the most common substances encountered in our diet. It is known to be a source of calories, and excess calories are known to lead to obesity, and obesity is known to lead to a host of other ailments. It is generally recognized that limiting sugar consumption is a good thing. But it turns out that sugar is more than a source of calories. The particulars of how our bodies respond to sugar are different from how they respond to starches, for example. Not all calories are equal. There is accumulating evidence that excessive amounts of sugar consumption over an extended period can initiate a cascade of chemical changes in our body and lead to everything from diabetes to cancer. Unfortunately, we don’t know how to define precisely what excessive consumption is and what an extended period might be. 

Given that this is medical science and a lot of money is at stake, there will be multiple studies coming to multiple conclusions. Taubes claims to have been studying this and associated issues for over a decade, and that he has come to agree with Lustig’s assessment. He also agrees that the data that support Lustig are not sufficient to convince all of the correctness of this hypothesis. We will present a short summary of the content of Taubes article. Those who find it thought provoking should follow the link to the complete article. Whatever one might conclude, it will be difficult to ever again engage in cavalier engorgement of sugar.

Gary Taubes discusses these issues in a fascinating article in the New York Times: Is Sugar Toxic? Taubes begins by introducing Robert Lustig as the latest, and perhaps most effective proponent of the hypothesis that sugar is poisonous at high consumption levels.

"In Lustig’s view, sugar should be thought of, like cigarettes and alcohol, as something that’s killing us."

Lustig brings impressive credentials to the argument.

"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."

As background, one needs to realize that sugar is a substance consisting of the chemical combination of a glucose molecule and a fructose molecule. It is the fructose that provides the sweetness. Whereas a starch provides glucose and calories, sugar’s calories come with the need for the fructose to be processed by the liver. So, all calories are not created equal. It is this path through the liver that is seen as the source of problems.

A basis for the suspicion that sugar might be bad for us resides in the observation that the human body evolved without ever encountering the high sugar levels that are common in modern diets. The most common natural source of sugar in the diet would be fruits. Ingesting sugar by chewing on a piece of fruit dilutes the sugar and spreads out the time over which it enters the blood stream and reaches the liver.

In our modern diet we encounter all sorts of highly concentrated forms of sugar that can enter our system rapidly.

"In animals, or at least in laboratory rats and mice, it’s clear that if the fructose hits the liver in sufficient quantity and with sufficient speed, the liver will convert much of it to fat. This apparently induces a condition known as insulin resistance, which is now considered the fundamental problem in obesity, and the underlying defect in heart disease and in the type of diabetes, type 2, that is common to obese and overweight individuals. It might also be the underlying defect in many cancers."

"If what happens in laboratory rodents also happens in humans, and if we are eating enough sugar to make it happen, then we are in trouble."

The liver is a complex organ with hundreds of functions within the body. The manner in which a fatty liver leads to insulin resistance is not completely clear. However, the correlation between the two conditions has been observed in humans.

"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’."

Other studies have indicated a correlation between high doses of fructose and insulin resistance in humans.

"Similar effects can be shown in humans, although the researchers doing this work typically did the studies with only fructose — as Luc Tappy did in Switzerland or Peter Havel and Kimber Stanhope did at the University of California, Davis — and pure fructose is not the same thing as sugar or high-fructose corn syrup. 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."

Why is insulin resistance such a critical phenomenon?

"You secrete insulin in response to the foods you eat — particularly the carbohydrates — to keep blood sugar in control after a meal. When your cells are resistant to insulin, your body (your pancreas, to be precise) responds to rising blood sugar by pumping out more and more insulin. Eventually the pancreas can no longer keep up with the demand or it gives in to what diabetologists call "pancreatic exhaustion." Now your blood sugar will rise out of control, and you’ve got diabetes."

"Not everyone with insulin resistance becomes diabetic; some continue to secrete enough insulin to overcome their cells’ resistance to the hormone. But having chronically elevated insulin levels has harmful effects of its own — heart disease, for one. A result is higher triglyceride levels and blood pressure, lower levels of HDL cholesterol (the "good cholesterol"), further worsening the insulin resistance — this is metabolic syndrome."

Taubes asks whether sugar may be even more dangerous than Lustig claims.

"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. The connection between obesity, diabetes and cancer was first reported in 2004 in large population studies by researchers from the World Health Organization’s International Agency for Research on Cancer. It is not controversial. What it means is that 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."

The connection seems to be related to high levels of insulin.

"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."

"What these researchers call elevated insulin (or insulin-like growth factor) signaling appears to be a necessary step in many human cancers, particularly cancers like breast and colon cancer. 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."

If sugar is a factor in causing insulin resistance, it will be a factor in causing cancers.

Taubes believes that more studies will have to be performed in order to convince doubters of the role of sugar in disease. Since the effects to be measured are subtle and occur over long periods of time, the studies will be long, costly and difficult. He is doubtful that major breakthroughs are on the horizon. There are an array of special interests that make their living selling sugar-laden products, and no specific agency to turn to for large-scale funding.

There seems to be sufficient data to conclude that sugar is more than just a source of calories. Since its supposed effects can work on thin people as well as the obese, it seems wise for all to consider moderation in its intake. But it is difficult to see it being considered a "poison" if one is unable to suggest what a harmful dosage might be.

Perhaps, the comparison with alcohol is the appropriate thought with which to finish. Alcohol can damage the liver if consumed in excess. But everyone’s liver is different and no fixed rule for consumption is accurate even for inebriation, let alone long-term liver damage. All we know is that moderate consumption is better than immoderate drinking.

Let a word to the wise be sufficient. Less sugar is in all ways a good thing.

No comments:

Post a Comment

Lets Talk Books And Politics - Blogged