Bad News for Sweets Lovers: Your Sugar Habit May Cause Breast Cancer

As if sugar doesn’t have enough PR problems, a new study published in January suggests it encourages the growth and spread of breast cancer tumors in rats. Common sugar is half fructose and half glucose, and the researchers showed that the fructose half shows particularly carcinogenic activity. This is similar to recent evidence that pancreatic cancer cells can distinguish between fructose and glucose — and perform better when fed the former.

Thus, the wagons of scrutiny are circling a little closer around sugar, and fructose in particular.

This idea, sometimes called the “fructose hypothesis,” refers to several studies suggesting fructose is processed differently in the body than other sugars and with more deleterious effects, including inflammation, obesity, fatty liver disease, diabetes, blood lipid levels and Alzheimer’s.

While present in many plant-based foods, fructose, or fruit sugar, isn’t necessary for any physiological function in the human body. In fact, we can’t even use fructose, so we must convert it to other forms of energy storage, like glycogen, fat, different sugars or other things like palmitate, the presence of which in diet is thought to promote heart disease.

Fructose in isolation thus represents the emptiest of calories, with only a slight bump of redeeming value owing to the fact that the body must spend energy to convert fructose to one of these other forms, an effort that burns an amount of energy roughly analogous to opening a Pepsi before drinking it. For those who don’t do much more than open processed foods, the many apparent deleterious effects of fructose are made worse by inactivity. The more active you are, it seems, the less you have to worry about fructose.

Glucose, meanwhile, is used by every cell in the body, 24/7. But we don’t need to eat glucose in order to have as much as we need. Starch, fat and every other form of energy storage, like fructose, can be converted to glucose. For all practical purposes, we can’t eat pure glucose without also consuming fructose. Table sugar is a 50/50 mix of the two, while in HFCS the ratio of fructose to glucose varies. Typically it’s 55/45 percent fructose-to-glucose, but can be as high as 90 percent fructose.

While glucose is processed everywhere in the body, fructose is only processed in the liver. Too much fructose can overload the liver’s capacity to deal, and cause a host of issues like insulin resistance, which leads to diabetes, and fat deposits in the liver, which can lead to liver disease and cancer. By depositing fructose-generated fat in our livers, we are basically turning them into human foie gras. But unlike those poor ducks, we are force-feeding ourselves by making food so addictive we can’t stop eating it. Fructose has been shown to be less satiating than other energy storage forms, which means you can eat more of it without feeling full.

So far the biggest challenge to the fructose hypothesis comes from a University of Toronto-based team led by Dr. John Sievenpiper, who argues many of the animal-based studies of the fructose hypothesis don’t apply to humans. Sievenpiper and his team recently produced a widely cited metastudy of strictly human studies which found little evidence that fructose is any worse than other forms of sugar, or other sources of calories, either, in terms of high blood pressure, diabetes and obesity.

These conclusions suit the current position of the junk food lobby, especially the idea that all calories behave equally, including those from fructose. It’s the same idea that was preached by the Global Energy Balance Network, a supposed nonprofit that was forced to shutter in shame after its close ties to Coca-Cola, including $1.5 million in funding, were disclosed.

Sievenpiper, meanwhile, received nearly $200,000 in unrestricted funding from Coca-Cola in 2014, according to the company’s disclosures, and has received funding from corn giant Archer Daniels Midland. He was retained by the Calorie Control Council as an expert witness in long-running litigation against a group of sugar companies that began with a fight over the corn syrup industry’s attempted use of the term “corn sugar.” The eventual out-of-court settlement had the feel of a ceasefire after a costly civil war; terms were not disclosed.

While industry shills most certainly aren’t helping clarify the matter, it’s also true there is little direct proof that, beyond a shadow of doubt, fructose-specific damage is occurring in humans. The growing number of circumstantial, anecdotal and animal-based pieces of evidence strongly suggests that this is so, but it’s problematic to micromanage the lifestyles and eating habits of human study participants to the same degree we do lab rats.

The new cancer study could not have been done on humans for practical and ethical reasons, but it nonetheless demonstrates a fructose-specific avenue for the genesis and spread of cancer. And it operates via biochemical and cellular pathways that we also possess.

“We determined that it was specifically fructose, in table sugar and high-fructose corn syrup, ubiquitous within our food system, which was responsible for facilitating lung metastasis and 12-HETE production in breast tumors,” the study’s co-author, Dr. Lorenzo Cohen, said in a press release.

So, does this mean we should look suspiciously at apples and oranges, because of all the fructose? On one hand, the fructose in whole fruit is tempered by fiber, which makes it overall less of a fattening food. On the other hand, our bodies evolved in circumstances where fruit was neither as abundant nor as sweet as it is today. Today’s fruits are more like juicy candy bars dangling from trees than the items our hunter/gatherer ancestors ate. But if you are as active as they were, maybe you can handle that much sugar.

If you’re thinking that maybe you should cut back to less than an apple a day, just in case, because you don’t get much exercise, here is a better idea: eat the apple, skip the soda and get some exercise. That's the CliffNotes version of what all of the evidence is telling us.