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White bread and other high glycemic index foods linked to lung cancer risk

White bread and other high glycemic index foods linked to lung cancer risk

food, junk-food and unhealthy eating concept - close up of white sliced toast bread on table

food, junk-food and unhealthy eating concept – close up of white sliced toast bread on table

TEXAS, United States, Wednesday March 9, 2016 – Eating foods with a high glycemic index has been linked to an increased risk of developing lung cancer, according to a new epidemiologic study from The University of Texas MD Anderson Cancer Center.

Glycemic index is a measure of the quality of dietary carbohydrates, defined by how quickly blood sugar levels are raised following a meal. Previous studies have investigated associations between GI and glycemic load (GL), a related measure of carbohydrate quantity, and risk of numerous other cancers.

In the United States, while lung cancer is the second most common cancer, it is by far the leading cause of cancer mortality, with over 150,000 deaths from lung cancer expected in the US this year, according to the American Cancer Society.

And while tobacco use remains the leading cause of lung cancer, it fails to account for all cases, particularly in those who never smoked.

The new research, published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research, represents the largest study to investigate potential links between glycemic index (GI) and lung cancer.

The findings also reveal that GI was more significantly associated with lung cancer risk in particular subgroups, including persons who had never smoked and those diagnosed with the squamous cell carcinoma (SCC) subtype of lung cancer.

According to Xifeng Wu, M.D., PhD, professor of epidemiology and senior author of the study, accumulating evidence suggests that dietary factors may modulate lung cancer risk.

Diets high in fruits and vegetables may decrease risk, while increased consumption of red meat, saturated fats and dairy products have been shown to increase lung cancer risk.

Stephanie Melkonian, postdoctoral fellow with Wu’s team and lead author of the study, went on to explain: “Diets high in glycemic index result in higher levels of blood glucose and insulin, which promote perturbations in the insulin-like growth factors (IGFs).”

“Previous research suggests increased levels of IGFs are associated with increased lung cancer risk. However, the association between glycemic index and lung cancer risk was unclear.”

To clarify the associations between GI, GL and lung cancer risk, the scientists surveyed 1,905 MD Anderson Cancer Center patients newly diagnosed with lung cancer and 2,413 healthy individuals recruited from other clinics.

Participants self-reported past dietary habits and health histories. Dietary GI and GL was determined using published food GI values, and subjects were divided into five equal groups, based on their GI and GL values.

According to Wu: “We observed a 49 percent increased risk of lung cancer among subjects with the highest daily GI compared to those with the lowest daily GI.
“The associations were more pronounced among subjects who were never smokers, diagnosed with squamous cell carcinoma or had less than 12 years of education.”

GL appeared to have no significant associations with lung cancer risk. “This suggests that it is the average quality, instead of quantity, of carbohydrates consumed that may modulate lung cancer risk,” Wu indicated.

When investigating volunteers who had never smoked, the researchers found that those in the highest GI group were more than twice as likely to develop lung cancer as those in the lowest group.

Among smokers, the risk was only elevated by 31 percent between the two groups. The relatively mild effects of a risk factor such as GI are more evident in the absence of the dominant risk factor, Wu explained.

The research team also noted stronger associations in those diagnosed with SCC and those with lower educational levels. Participants in the highest GI group were 92 percent more likely to develop the SCC subtype compared to the lowest GI group, possibly due to the influence of elevated IGFs on SCC development.

Among those with fewer than 12 years of education, subjects in the highest GI group were 77 percent more likely to develop lung cancer than those in the lowest GI group. This contrasts with an elevated risk of only 33 percent in subjects with more than 12 years of education.

The researchers indicated that educational level is a proxy for socioeconomic status, which has been linked with diet quality and smoking behaviours. The associations between GI and education may therefore reflect the joint impact of poor diet and smoking on lung cancer risk.

The scientists noted several limitations to the study, including the fact that it was limited to non-Hispanic whites. It was also a retrospective study, subject to errors in recall of past dietary intake, and the study did not account for diabetes, hypertension or heart disease in their subjects.

The authors noted that future work must incorporate prospective cohort studies in other ethnic groups in order to validate a causal relationship between GI and lung cancer. They also want to further investigate the underlying mechanisms by which GI may influence the risk of lung and other cancers.

“The results from this study suggest that, besides maintaining healthy lifestyles, such as avoiding tobacco, limiting alcohol consumption and being physically active, reducing the consumption of foods and beverages with high glycemic index may serve as a means to lower the risk of lung cancer,” Wu said.

While specific dietary recommendations could not be made on the basis of their results, the authors suggested limiting foods and beverages with high GI, such as white bread or bagels, corn flakes and puffed rice, for a more balanced diet and to lower the risk for lung cancer and chronic diseases. Examples of low GI foods include whole-wheat bread, pasta, and rolled or steel-cut oatmeal.


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