Scientists from the University of Texas MD Anderson Cancer Center have found that people who eat a diet full of high glycemic index foods—think processed white bread, bagels, white rice, baguettes—had a 49% higher risk of developing lung cancer, even if they've never smoked a single cigarette.
The study, which was published in Cancer Epidemiology, Biomarkers & Prevention this week, is the largest ever to investigate the potential links between glycemic index and lung cancer, according to the authors. A glycemic index is a measurement of how rapidly carbohydrates elevate blood sugar levels in the body. The higher the glycemic index, the more rapidly blood sugar levels rise after a meal which results in elevated levels of blood glucose and insulin. That in turns raises what's called insulin-like growth factors, which are linked to an increased lung cancer risk, according to the scientists.
Scientists at MD Anderson surveyed 1,905 patients newly diagnosed with lung cancer and another 2,413 healthy individuals, all non-Hispanic whites. Those subjects reported their past dietary habits and health histories, and they were then divided into groups based on their associated glycemic index and glycemic load, a measure of carbohydrate quantity.
"We observed a 49% increased risk of lung cancer among subjects with the highest daily glycemic index compared to those with the lowest daily glycemic index," said Xifeng Wu, professor of epidemiology and senior author of the study. "The associates were more pronounced among subjects who were never smokers."
Interestingly, there was no link between the glycemic load—i.e. the quantity of carbohydrates consumed—and lung cancer, which suggests that it's the quality, not the amount of carbohydrates, that has the biggest effect on lung cancer risk, said Wu.
Lung cancer is the second most common cancer among both men and women in the U.S. It's also the leading cause of cancer mortality, with over 150,000 deaths from lung cancer expected in the U.S. this year alone, according to the American Cancer Society. Smoking and tobacco use is still the leading cause, though it doesn't account for all cases. Researchers had long suspected a link between a high-glycemic index diet and lung cancer risk, but the link between the two was unclear until now.
Among non-smokers in the study, those within the highest glycemic index group were more than twice as likely to develop lung cancer as those in the lowest group. For smokers, the difference was elevated by 31% between the two groups.
“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,” said Wu.
Low glycemic index foods include things like 100% stone-ground whole wheat bread, rolled or steel-cut oatmeal, most fruits, and non-starchy vegetables.