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Sugar Is Toxic: Heart Disease, Cancer & More

This is Part 1 in a 4-part series on Sugar and Other Sweeteners.

(1) Sugar Is Toxic: Heart Disease, Cancer & More
(2) Sugar: How Much Is Too Much?
(3) Artificial Sweeteners Make You Fat
(4) Sugar: Physical Addiction or Emotional Craving?

I always thought that sugar was just empty calories, that the worst it could do was make people chubby – a threat to beauty, not to life. Then I saw a disturbing 60 Minutes broadcast called Is Sugar Toxic?, interviewing scientists about the relationship between sugar and cardiovascular disease, cancer, and addiction. The scientists doing the research said that sugar was a direct cause of disease, that the added sugar in our diet was a chronic toxin, not just empty calories. Most of them had stopped eating sugar themselves.

This scared me, so I started to do some research of my own.

Different Types of Sugar

Table sugar, or "sucrose", is comprised of two simple sugars bonded together: 50% fructose, 50% glucose. Raw sugar has the same composition; there is no benefit. Brown sugar is just sucrose with molasses – same basic composition.

Glucose, or "blood sugar", is the sugar that circulates in your blood. Fructose, or "fruit sugar", is found in plants and honey. It’s the fructose in sugar that causes the problem, as you will see. That doesn’t mean you shouldn’t eat whole fruit; whole fruit contains fiber that slows digestion. It does mean that fruit juice poses a danger. Fruit juice, a processed food, is as dangerous to health as soda.

Generally it’s added sugar that’s the danger – or juice, because it’s been processed to remove the fiber.

High Fructose Corn Syrup (HFCS) has been vilified, but actually it’s only slightly higher in fructose than table sugar: 55% fructose, 45% glucose. The difference is trivial. They’re equally bad for you. Unsweetened apple juice, however, is 64% fructose – much higher.

Worse of all is agave syrup (sometimes called "agave nectar", though it’s made from the root of the plant, not the sap). The internet echo chamber says that agave syrup is 55-90% fructose or 70-97% fructose, depending on the brand. A researcher writing for the Weston Price Foundation actually tested samples from the two manufacturers that make virtually all the agave syrup in the US. He found that agave syrup is 70-85% fructose, with the other 15-30% being glucose.

The Weston Price article gives the sugar breakdown of two other sweeteners it tested. The raw honey was 39% fructose, 32% glucose, and 17% water, and the maple syrup was 29% fructose, 30% glucose, and 32% water. The remainder was other stuff – particulate matter, enzymes. So honey is roughly 40% fructose, and maple syrup is roughly 30% fructose – lower. But don’t go running to the store yet – that’s still a lot.

Sugar: The Bitter Truth

When you eat sweeteners such as sugar, HFCS, honey, or maple syrup, your body breaks them down into their component simple sugars, glucose and fructose. These are metabolized by your body very differently. The difference is why fructose is toxic and glucose is not.

My overview of sugar metabolism is largely based on a 2009 lecture called Sugar: The Bitter Truth [VIDEO] by Dr. Robert Lustig, a pediatric endocrinologist. This video has gone viral; it’s been viewed on YouTube more than 2.4 million times (twice by me – it’s rather dense). Here’s a link to the slides from the presentation [PDF] (most of them, anyway). They are hard to read in the video.

The video is 1.5 hours long and starts with a friendly and accessible introduction to the history of sugar, HFCS, and their association with disease (it’s worth watching just for that). Then, speaking very quickly, Lustig goes into excruciating detail on the biochemistry of glucose, ethanol, and fructose metabolism, and why fructose does essentially the same damage to the body as alcohol (ethanol) – "beer belly", fatty liver, etc. If you aren’t already versed in biochemistry, it’s hard to follow. However, I found an almost word-for-word summary on the Mercola site.

The only part of Mercola’s post that doesn’t come from Lustig’s lecture is the recommendation at the end to eat raw sugar or honey in moderation. Lustig would never say that. Raw and refined sugar are the same food, and he knows it. Lustig recommends John Yudkin’s book, Pure, White, and Deadly, in his lecture (the US edition is titled Sweet and Dangerous), and Yudkin goes on and on about this, describing sugar processing in detail. (I was lucky enough to find an affordable copy of Yudkin’s hard-to-find book.) Honey is hardly any better, at 40% fructose. I’ll talk about Lustig’s recommendations for how much sugar is safe in Part 2 of this series.

Sugar Metabolism: Disease & Appetite Run Wild

Sugar is 50% glucose, 50% fructose. So every time you eat sugar, you get a substantial hit of fructose. Glucose won’t hurt you, but fructose will. Here are the important ways in which glucose and fructose metabolism differ:

    Glucose Metabolism
  • 80% metabolized throughout the body, 20% metabolized in the liver – little strain on liver.
  • Only 0.4% of glucose calories are metabolized in the liver as VLDL (bad cholesterol).
  • Raises blood sugar, causing secretion of insulin, causing secretion of leptin (appetite control hormone) – you get the “I’m full” signal.
  • Suppresses ghrelin, a hormone that gives a feeling of hunger – you stop feeling hungry.
    Fructose Metabolism
  • 100% metabolized in the liver – big strain on the liver.
  • Produces uric acid as a waste product – excess uric acid causes gout.
  • Uric acid blocks the enzyme that makes nitric oxide, which keeps blood pressure low – causes hypertension.
  • Increases fat synthesis – causes obesity. One study found 30% of fructose was stored as fat, versus 0.5% of glucose.
  • Increases VLDL and triglycerides – risk markers for cardiovascular disease.
  • Transport of VLDL to adipose sites causes insulin resistance (it takes more and more insulin to remove glucose from blood) leading to type 2 diabetes.
  • Insulin resistance causes hyperglycemia, leading to organ and nerve damage.
  • Insulin resistance causes elevated insulin, leading to heart disease and cancer.
  • Raised triglycerides prevent leptin from crossing the blood-brain barrier so you don’t get the “I’m full” signal, plus elevated insulin makes you always feel hungry.
  • Fails to suppress ghrelin – you feel hungry all the time.

Basically, fructose causes Metabolic Syndrome, which consists of three of the following: expanding waist, high triglycerides, low HDL, high blood pressure, high fasting glucose. Metabolic syndrome is a risk factor for cardiovascular disease and diabetes.

Fructose also interferes with appetite control in multiple ways. When you eat sugar, you can’t trust your hunger signals to tell you when you are hungry and full. This is critical – especially if you are trying to eat according to body wisdom.

This damaging scenario is most likely to happen like this when large amounts of fructose hit the liver quickly. This happens with any food with added sugars, but it happens most quickly when you take sugar in liquid form as a sweetened beverage, or when you eat sweet foods on an empty stomach.

Lustig says that exercise can help, not because it burns off calories, but because it speeds up your metabolism. This can allow you to burn off the fructose before it gets to the fat creation part of the metabolic process. But presumably, there are limits – begging the question, how much is safe to eat? This will be addressed in Part 2.

Sugar & Cancer, Sugar & Ulcers

Cancer researchers have discovered that elevated insulin, along with a related hormone called "insulin-like growth factor", promote tumor growth and may even cause cancer. Lewis Cantley, a researcher from Harvard, says that perhaps 80% of all human cancers are driven by high levels of insulin. Craig Thompson, a researcher at Memorial Sloan-Kettering Cancer Center in New York, thinks that many pre-cancerous cells would not become malignant tumors if not driven by insulin to take up and metabolize more blood sugar.

Both Thompson and Cantley told Gary Taubes that they eat as little sugar as possible due to the cancer risk. Cantley said the same thing to 60 Minutes’ Sanjay Gupta: He advised that people not eat sugar or at least keep it to a minimum, adding, "In fact, I live my life that way. I rarely eat sugar."

Yudkin mentions other diseases associated with sugar, based on his own research. For example, eating a lot of sugar appears to cause gastric and duodenal ulcers. He found both epidemiological and experimental evidence. He put young men on a high sugar diet for two weeks, then got them to swallow a gastric tube first thing in the morning. He found that their gastric juices were 20% more acidic and their enzyme activity increased three-fold, both at rest and after a mild meal. This is what causes ulcers. He also did experiments that confirmed that low-sugar diets improved the symptoms of ulcer patients.

Yudkin found evidence for virtually all of the now-verified associations between sugar and disease – heart disease, gout, cancer, and more. Too bad no one listened to him back in 1972. But no, we went with Ancel Keys and his competing "saturated fat" hypothesis, which has been pretty well debunked at this point.

There’s no doubt now that sugar causes heart disease, cancer, obesity, and more. But do we have to stop eating it entirely? How much sugar can you safely eat, and how much is too much? This is the question I’ll address in Part 2.

Thoughts? Comments? I’d love to hear them.