More bad news for carb lovers: The same refined, low-fiber foods that contribute to obesity, diabetes and other serious conditions are now believed to increase one’s risk for cancer—and to worsen outcomes in those who already have it.

Alarming new finding: In a study recently published in Cancer Epidemiology, Biomarkers & Prevention, people who ate the most high-glycemic (blood sugar–spiking) carbohydrates—foods such as white bread, white rice and russet potatoes—were 49% more likely to be diagnosed with lung cancer than those who ate the least.

Even though this isn’t the first study to link “junk” carbohydrates to cancer, the evidence has now gotten strong enough that more and more medical experts are advising us to take a very close look at the quality of the carbs that we eat.


Dietary carbohydrates are a critical driver of blood sugar (glucose) levels and must be tracked by people with diabetes to keep their blood glucose levels steady.

One of the most effective tools to do this is the glycemic index (GI), a ranking system of carbohydrates, which shows how quickly different foods increase levels of blood glucose. High-GI carbs raise blood sugar almost instantly…lower-GI foods (the “good” carbs, such as chickpeas, prunes and pearled barley) raise it more gradually.

We have known for a long time that people with diabetes are more likely to get cancer than those who do not have diabetes. More recently, we’ve learned that even in the absence of diabetes, many people are “prediabetic,” with elevated blood glucose and insulin (the blood sugar–regulating hormone)—due to poor diet, a lack of exercise and other causes. Prediabetes makes people more likely to develop cancer…and puts them at greater risk for poor outcomes when they do.

Recent finding: A variety of cancers, such as breast, colorectal, endometrial and pancreatic, seem to be affected by high glucose and high insulin. It is clear that a “Western-style” diet—typically loaded with  high-GI foods—creates some of the conditions that make it easier for cancers to thrive. What happens…

  • High-GI foods trigger an increase in insulin, which results in a rise in insulin-growth factor (IGF-1). Both insulin and IGF-1 will promote the growth of cancer cells and inhibit their natural death.
  • Obesity, particularly when there is excess fat in the belly area, is strongly associated with prediabetes, along with higher blood glucose and insulin. People with obesity have more inflammation, oxidative stress and estrogen—all of which increase cancer risks.


Unless you already have diabetes or are at a high risk of developing it (for example, you are overweight or obese with belly fat* and/or have a sedentary lifestyle), I don’t advise too much emphasis strictly on total carbohydrate intake or GI food ratings. I focus more on the quality of carbohydrates and, in practice, find that people who try to track the GI of all the foods they eat tend to give up healthy eating altogether because it becomes too much work.

Also, high-GI foods are just one part of the equation. Vegetarians (who generally eat low-GI foods) tend to have a lower risk for cancer. But is it because of their carbohydrate choices or because they’re also more likely to be physically active and have lower body weights? The evidence isn’t clear.

My advice: Follow an overall strategy that both controls blood glucose and may help you prevent/manage cancer. Key steps…

Limit weight gain through a prudent diet and physical activity.  You don’t have to avoid all high-GI foods, but you should limit them. Consider eating plans (such as the Mediterranean diet) that emphasize whole grains, legumes, vegetables and other low-GI foods. Such diets have been linked to reduced risk for cancer-promoting obesity, diabetes and elevated blood glucose levels. Regular exercise has also been linked to a reduced risk and improved survival in many cancers—in part, by reducing insulin.

Avoid processed foods as much as possible. They tend to be high in added sugar, which raises blood glucose very quickly. One of the worst: Sugared soft drinks, which typically have the equivalent of 10 teaspoons of sugar per serving!

Important: Don’t wait. Cancer usually develops after decades of exposure to high blood glucose, insulin, etc. The sooner you start eating a healthy diet, the better.

Cut back on red meat. It is among the main sources of saturated fat in the American diet. Even if you mainly eat healthy carbohydrates, too much saturated fat increases the risk for insulin resistance (when the body becomes less sensitive to the hormone’s effect, triggering the release of more insulin to compensate) and cancer.

Improve your gut health. A healthy intestinal “flora” can help prevent obesity, along with preventing both insulin resistance and inflammation. It’s another argument for eating low-GI carbs—they tend to be high in fiber and act as prebiotics, foods that promote the growth of healthy intestinal bacteria.

Ask about metformin (Glucophage). It’s a diabetes drug that reduces insulin resistance, decreases the production of glucose by the liver and lowers insulin levels. It’s also less likely to cause weight gain than other diabetes medications. One large study found that it can reduce overall cancer risk by 31% in people with diabetes.   

But it is not a miracle drug. Research has shown that lifestyle changes are more effective than metformin at preventing diabetes. Even so, more people should be taking it, particularly those who have trouble controlling high blood glucose/high insulin with diet and exercise alone.


If you have cancer, try your best to stay active and eat well—during and after treatments. It’s common for cancer survivors to deal with stress by overindulging in comfort foods. But research shows that those who maintain a healthy weight, are physically active and eat nutritious, low-GI carbs will be less likely to have a cancer recurrence.

*Abdominal obesity is defined as a waist measurement of 40 inches or more in men and 35 inches or more in women.