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More Bad News For Carbohydrates

Colorectal cancer risk boosted by sugar and refined starches

Regular readers of this column won’t be surprised to learn that diets high in sugar and refined starches increase the risk of disease recurrence and death in people who have been treated for colorectal cancer.

However, the extent of the recurrence risk may shock you, as it did me: according to a new study, people treated for Stage 3 colorectal cancer (in which tumor cells have spread to lymph nodes) and who were eating diets rich in sugar and refined carbohydrates were 80% more likely to experience a recurrence or die of the disease than those eating carbohydrates with the lowest glycemic impact. Among patients who were overweight or obese, the increase was even greater.

More than 1,000 patients participated in the study whose results were published this week in the Journal of the National Cancer Institute (1). The patients had undergone surgery and participated in a National Cancer Institute-sponsored Cancer and Leukemia Group B clinical trial of follow-up chemotherapy for their disease.

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The subjects reported their dietary intake during and six months after the trial and researchers tracked their total carbohydrates, as well as their glycemic index (a measure of how sharply blood glucose levels rise after eating a particular food), and glycemic load (which takes into account the amount of a carbohydrate consumed), and then analyzed the data for a connection between these measures and the recurrence of colon cancer.

“In light of our and others’ research, we theorize that factors including a high glycemic load may stimulate the body’s production of insulin,” commented lead author Dr. Jeffrey Meyerhardt, a medical oncologist at the Dana-Farber Cancer Institute in Boston. “That, in turn, may increase the proliferation of cells and prevent the natural cell-death process in cancer cells that have metastasized from their original site.”

There is mounting evidence that colorectal cancer survivors whose diet and sedentary lifestyles lead to excess amounts of insulin in the blood have a higher risk of recurrence and death from cancer. High insulin levels can be caused by eating too many sugary and starchy foods – especially refined starches like white flour and rice and any foods made with these. Insulin – and a closely related hormone, insulin-like growth factor 1 (IGF-1) – are known to promote the growth and spread of cancer cells. Moreover, high levels of glucose in the blood – which typically follows the ingestion of sugary or starchy foods – are also thought to fuel tumor growth.

In a previous study (2) of advanced-stage colon cancer patients, Meyerhardt and his colleagues had found that those with a typical “Western” diet—marked by high intakes of meat, fat, refined grains, and sweet desserts—were three times more likely to have a cancer recurrence than those whose diets were least Western. This latest study was conducted to explore which component of the Western diet is most responsible for the increased risk of recurrence.

So – does this mean carbs are off the menu? Don’t worry – I don’t recommend anything that drastic, nor does Dr. Meyerhardt.

“Different carbs and sugar lead to different responses in your body,” he told the New York Times. “I think people should focus on a well-balanced diet” and substitute foods associated with lower glycemic loads or carbs for foods that have higher levels.

Mediterranean Diet To The Rescue

Enter the Mediterranean diet. (I mean the traditional, pre-WW2 Mediterranean diet, not the modern one featuring pasta, white bread, instant polenta and the ultimate abomination: Let’s Pizza (watch this hair-raising video).

As I have described in previous posts, traditional Mediterranean eating-patterns are characterized by low-glycemic foods such as vegetables, fruits, lentils, chickpeas, nuts, healthy oils, fish, lean meats and whole, fermented grains.

This way of eating has a considerably lower glycemic impact than diets rich in refined grains (boxed breakfast cereals and instant oatmeal, granola bars and candy bars (often the same thing!), factory-made bread and wraps (where whole grain isn’t much better than white), assorted cakes and cookies, bagels and pretzels (dried or fresh), pasta, rice and rice cakes) and the many processed starches used to make convenience food.

This was elegantly illustrated by a study published earlier this summer that compared the metabolic impact of three different diets – low-fat, low-carbohydrate and low-glycemic-index – in overweight young adults (3). It found that the low-glycemic Mediterranean-style diet based on healthy carbohydrates—rather than a low-fat or low-carbohydrate diet—offers the best chance of keeping weight off sustainably, without bringing unwanted side effects such as an increase in unhealthy blood fats or inflammation – as in the case of the other two diets.

So you don’t need to eliminate all carbs to be healthy; just eating whole, fresh foods with a low-to-moderate glycemic impact can make a big difference. Not just by reducing our risk of cancer (both its development and its recurrence), but also by helping us maintain healthy weight (excess weight is a key cancer risk factor) and steady energy levels (which go hand-in-hand with steady blood glucose levels).

If you want to know more about the theory and practice of Mediterranean-style eating, why not consult my book, Zest for Life: The Mediterranean Anti-Cancer Diet. And to see how tasty and simple low-glycemic diets can be, check out my free Mediterranean-Diet cooking videos on YouTube.

References

(1) Meyerhardt JA, Sato K, Niedzwiecki D. Dietary Glycemic Load and Cancer Recurrence and Survival in Patients with Stage III Colon Cancer: Findings From CALGB 89803. J Natl Cancer Inst (2012) doi: 10.1093/jnci/djs399 First published online: November 7, 2012.

(2) Meyerhardt JA, Niedzwiecki D, Hollis D et al. Association of dietary patterns with cancer recurrence and survival in patients with stage III colon cancer. JAMA. 2007 Aug 15;298(7):754-64.

(3) Ebbeling CB, Swain JF, Feldman HA, Wong WW, Hachey DL, Garcia-Lago E, Ludwig DS. Effects of dietary composition on energy expenditure during weight-loss maintenance. JAMA. 2012 Jun 27;307(24):2627-34.

Conner Middelmann Whitney is a nutritionist, journalist, chef, and former cancer patient.

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