Do you fear sugar might cause cancer?

According to media headlines last week, a new study linked white bread and sugary foods to cancers and disease. Another study, which didn’t make headlines, reported that such foods were not associated with cancers. The data in both studies actually showed the same thing. Which conclusions do we believe?

Does sugar feed cancer?

The idea that sugar feeds cancer, if it was true, would understandably terrify anyone. It is this belief, though, that has helped to feed fears of refined sugars and flours and other ‘bad’ carbohydrates.

Recent stories circulating the internet and media have led many people to think that concerns over sugars are real and that they come from upstanding doctors at prestigious institutions. No one can blame them for believing sugar is linked to cancer. There are more than one million websites (a stunning 1,080,000 by last count) capitalizing on this fear and virtually none offering the science.

But it is nothing more than an urban legend, the result of misunderstood and distorted science.

The legend even finds its way into our inboxes, sent to us by concerned friends or relatives. Did you get the email called the Cancer Update, for example? It claimed to be from Johns Hopkins, saying sugar feeds cancer cells and suggesting people eliminate refined carbs and sugars to “starve cancer cells” and prevent the spread of cancer. It also claimed that nutritional deficiencies purportedly due to modern diets and lifestyles can cause cancer, that acidic foods like meat cause cancer, that ‘live enzymes’ in raw vegetables and various supplements can fight cancer, and that cancer is a disease of the spirit and caused by having a negative outlook.

It was a hoax and the information was of the “quack variety,” as Snopes** reported. The information was based on vitalism. [Vitalism is at the heart of most beliefs and fears of the special powers of foods and supplements, but it defies known scientific principles of physics, chemistry and biology. It’s an ages-old mysticism that holds that whole, natural foods have vital life energy, live enzymes and vibrant nutrients, a special essence, that can impart optimal wellness and heal and prevent disease; while refined or cooked foods are unhealthy and the nutrients our bodies use from them are inferior, cause aging and chronic diseases, and feed cancer.] The spoof became so widespread and potentially harmful, though, that Johns Hopkins even issued a public statement last March saying it had never published that information and doesn’t endorse its contents.

Even if one believed sugar feeds cancer, although it might sound logical that eliminating sugar from one’s diet could then stop cancer cells from growing, that’s biologically not how our bodies use food. All food energy — regardless of its source — is converted into identical simple sugars that our bodies use for energy to function. Similarly, our bodies use the same chemical nutrients from foods - regardless of their source. Just like healthy cells, cancer cells don’t care where the sugar comes from. And if you stopped eating completely, your body would then start tearing down fat and muscle stores for energy, but it wouldn’t stop the cancer until you died of starvation. Please don't try this. Following this faulty logic would seriously endanger the life and chances of a cancer patient who needs greater nutritional intakes, not more restrictive diets.

The sugar-cancer fear has the veneer of science, fueled by reports made to appear scientific. Like all food fears, this one is nothing new. Each time it’s been debunked, it resurfaces using a different technique or elaborate theory attempting to convince us that it is based on science.

The root of this myth is experiments by German scientist, Otto Warburg, Ph.D., who won the 1931 Nobel laureate in medicine. He reported that cancer cells produced lactate from glucose in the presence of oxygen, where normal cells produced lactate from glucose in the absence of oxygen. This observation led him to conclude that energy metabolism in cancer cells was different and was misinterpreted to mean that dietary “sugar feeds cancer.” By 1961, scientific research had identified the metabolic pathways in all cells and shown that energy metabolism is the same as those in cancer cells, but the myth was born.

But there is no truth to the rumor that sugar causes cancer, or that people with cancer shouldn’t eat sugar because it causes cancer to grow faster, said Dr. Timothy Moynihan, M.D., a cancer specialist at Mayo Clinic, in Rochester, Minnesota. He debunked this popular misconception in a recent article, explaining:

Sugar doesn't make cancer grow faster. All cells, including cancer cells, depend on blood sugar (glucose) for energy. But giving more sugar to cancer cells doesn't speed their growth. Likewise, depriving cancer cells of sugar doesn't slow their growth.

This misconception may be based in part on a misunderstanding of positron emission tomography (PET) scans. Doctors use PET scans to help determine the location of a tumor and see if it has spread. During a PET scan, your doctor injects a small amount of radioactive tracer — typically a form of glucose — into your body. All tissues in your body absorb some of this tracer. But tissues that are using more energy — exhibiting increased metabolic activity — absorb greater amounts.

Tumors are often more metabolically active than healthy tissues. As a result, they may absorb greater amounts of the tracer. For this reason, some people have concluded that cancer cells grow faster on sugar. But this isn't true.

Study #1: “Bad” carbs are bad...

But that hasn’t stopped people from continuing to blame cancer on sugars. This new study was reported by the media as having found “conclusive evidence” that eating sugary cereals, white bread and other carbohydrates with high glycemic index increase risks of cancer and other modern “lifestyle diseases.”

Glycemic index. One of the techniques being used recently to define a ‘healthy’ food is its glycemic index or a diet’s glycemic load. Glycemic index is a measure of foods’ immediate effects on blood sugars, and glycemic load considers the glycemic index in the proportion of carbohydrates in foods. The thinking is that foods that take longer to digest will have lower GI levels and be healthier because they won’t tax the body with surges in blood sugar and insulin levels. For centuries, refined carbohydrates and white baked goods have been blamed for causing every imaginable ill, including obesity, heart disease, diabetes and cancer. It’s similar to equally-old fears (which science has continued to find no credible evidence to support) surrounding sugar highs in normal people and that temporary fluctuations in blood insulin and glucose levels could lead to obesity and disease. The evidence on the roles of glycemic index and sugars in diabetes and obesity have previously been covered.

This paper, published in the American Journal of Clinical Nutrition, was a meta-analysis of 37 published observational (epidemiological) studies that had looked for correlations between glycemic index/load and diseases. No cohort or clinical intervention trials were included. The studies that the Australian authors compiled had differing designs: different age subjects; different study durations; different techniques to identify diseases (self-reported, chart reviews and only 4 involved actual physical exams); and had adjusted for different confounding factors known to contribute to disease. “Most of the studies used basic models, controlling for age and sex only,” however, the authors admitted.

The studies used a food frequency questionnaire at enrollment to calculate GI/GL, but all used different units to report levels, so the authors converted the results to a single scale. The authors noted that a significant limitation of their meta-analysis was that none of the studies they included had “actually validated the assessment of GI or GL using another dietary method or against an objective standard. The assignment of GI values to foods in a nutrient database is to some extent subjective,” they wrote, “and may be unreliable when extrapolating from one country to another.” They then separated out ten different diseases (type 2 diabetes, heart disease, stroke, breast cancer, colorectal cancer, pancreatic cancer, endometrial cancer, ovarian cancer, gastric cancer and gallbladder disease) and compiled the different risk ratios associated with GI/GL reported in each study.

This paper epitomized the weaknesses of meta-analyses, which lump together diverse and weak or null studies hoping to derive a significant effect. These problems make it imperative that any correlations that emerge from such analyses are tenable and clear; and beyond random chance, statistical modeling errors and confounding factors.

To cut to the chase, try as they might, they were unable to find a viable correlation between GI/GL and any disease. None of the 37 studies, separately or lumped together, could come up with a tenable link. The relative risks for all of the diseases hugged either side of null (relative risk 1/1 = 1):

The researchers, however, arrived at a different conclusion:

This meta-analysis provides high-level evidence that diets with a high GI, high GL, or both, independently of known confounders, including fiber intake, increase the risk of chronic lifestyle-related diseases. The effect was modest overall... Overall, the GI had a more powerful effect than did the GL... The findings indicate that the judicious choice of low-GI foods offers a similar or higher level of protection as whole-grain foods or high fiber intake in the prevention of chronic lifestyle-related disease.

Are we being sold something?

When a study’s conclusions contrast so dramatically with the actual data, it is helpful to ask why.

Not mentioned by any news reporter was that, except for the statisticians, the researchers who conducted this study are authors of GI diet books. Not only that, but they are with a GI testing service and a GI-based licensing program in Australia. Through the GI Symbol Program run out of the University of Sydney, food companies purchase license agreements with Glycemic Index Ltd. to put its GI symbol on their products. It’s a marketing gimmick, a “seal of approval” to identify foods for shoppers that are the “healthier choices.” The study’s lead author, Alan Barclay, is the founding director of GI Ltd., the company behind Australia’s GI Symbol Program, which is under the direction of another of the study authors, Jennie Brand-Miller.

As Barclay wrote on their company blog, examples of foods that are healthier choices for kids include:

Sunripe School Straps and Go Fruits

Uncle Tobys Crunchy and Chewymuesli bars

Maggi 2 Minute Noodles

Nestle All Natural 99% Fat Free and Nestle Diet Yoghurts

Brownes Diet Yoghurts

In addition, writes Barclay, “Nestle Australia has just brought out two new healthy low GI dairy snacks designed especially for kids:”

Nestle Milo Mousse Energy Dairy Snack

Nestle Milo Energy Dairy Snack

A few weeks ago, it landed another huge account. USANA Health Sciences, Inc. announced that its Nutrimeal meal replacement will carry the “coveted GI Symbol.” It’s part of UNSANA’s RESET diet program, a “holistic approach to setting you on the path to a healthier way of life.” USANA is an international dietary supplement company, based in Salt Lake City, Utah, with $374 million in net sales in 2006. As the company says, its “nutritionals are designed to provide the micronutrients (vitamins, minerals, antioxidants, and other compounds) your body needs for optimal, lifelong health by providing a complete and balanced spectrum of nutrients and antioxidants to help counteract poor nutrition and free-radical damage.”

For those unfamiliar with USANA, it is a multi-level marketing scheme, a form of direct sales where independent distributors sell products, usually in homes or by telephone, and in turn, they are told they can make money in a pyramid method from their own sales, as well as from those of people they recruit. See MLM Watch by Dr. Stephen Barrett, M.D., and the National Council Against Health Fraud for the full scoop on MLMs.

With so much money and careers at stake in finding evidence to support low-GI foods, and in worrying people that high-GI foods could cause diseases and health problems, it might help explain why this study’s null findings were interpreted positively. Even the confirmation bias of well-meaning professionals can lead them to see proof of what they believe when the evidence disproves it.

It’s not science itself that we can’t trust, it’s the bad portrayals of science. Seeing for ourselves the actual null and negative findings, as was evident in all 37 studies on nearly 2 million people used in this analysis, offers us the most valuable information. If a significant correlation had been found and had biological plausability, a possible cause might then be tested by conducting randomized, controlled intervention clinical trials. If an epidemiological study can find no significant correlation, no link, between a food or ingredient and a disease, then there is nothing to base a suggestion for a causal link. It's a nonissue.

Null findings testing an hypothesis are important, as they enable science, and us, to move on, rather than continue to beat a dead horse or needlessly worry. This is the source of Albert Einstein’s famous saying: “No amount of experimentation can ever prove me right; a single experiment can prove me wrong.”

Study #2: No support for sugar fears

The second study was of no interest to PR agencies, and hence, never made the news. This epidemiological study, was published in the International Journal of Cancer. Its data was from 120,852 people in the Netherlands Cohort Study, who’d also completed food frequency questionnaires in 1986.

After 11.3 years of follow-up, the researchers found no genuine relative risk for colorectal cancers related to dietary glycemic index or glycemic load among the men or women. They also found no clear associations between any cancer subsite and dietary factors. Relative risks for cancers associated with sugary, high-glycemic foods ranged from 0.83 to 1.20. The relative risks all hugged either side of null (RR=1) with none tenable, like the other observational studies.

Unlike the previous study, however, these researchers reported their findings factually: “Overall, our findings do not support the hypothesis that a diet with a high glycemic load or index is associated with a higher risk of colorectal cancer.” And conversely, low-glycemic foods aren’t associated with lower risks. There is no link.

As hard as some have tried to prove that their believed way of eating is the only right way and can lead us all to optimum health and wellness, while preventing cancer and chronic diseases of aging; the facts continue to show that well-fed people around the world have hugely varied diets with no consistent correlations with health or longevity. More important, efforts to scare us about foods some don’t believe we should be eating and to prove that ‘bad’ foods can give us cancer or some other frightening disease have no credible evidence, either. If beliefs were about science, they wouldn’t be beliefs, I guess.

© 2008 Sandy Szwarc

** Snopes refers to the Urban Legends Reference Pages, a website that investigates urban legends, internet rumors, emails, viruses and other stories that are part of our pop culture. Anytime you hear or read anything online that you’re not sure is true, check it out at Snopes. The authors, Barbara and David Mikkelson, have probably debunked it.