Researchers suggest a high-GI diet may raise the risk of lung cancer.
High-GI foods increase blood glucose levels more than moderate- or low-GI foods. High-GI foods include white bread, short grain white rice, melon and pineapple, while low-GI foods include sweet potato, corn, legumes and lentils.
Glycemic load (GL) is a measure linked to GI, which uses the GI value of a food to calculate how much carbohydrate is in a specific food serving and how quickly that food serving will raise blood glucose levels.
According to senior study author Dr. Xifeng Wu, of the Department of Epidemiology at the University of Texas MD Anderson Cancer Center, previous research has investigated how the GI of a diet is associated with certain types of cancer, including stomach, colorectal and pancreatic cancers.
However, the team notes that less is known about how the GI of foods is linked to lung cancer - something they set out to investigate in this latest study.
49% greater lung cancer risk with a high-GI diet
The researchers analyzed the data of 1,905 participants with lung cancer and 2,413 healthy controls who were part of an ongoing lung cancer study at MD Anderson.
As part of the study, the participants underwent in-person interviews, in which they were asked to disclose their health history and dietary behaviors.
The team calculated the GI content of participants' diets using GI values given to foods in the 2008 International Tables of Glycemic Index and Glycemic Load Values. Participants were divided into quintiles based on their results.
Compared with participants who were in the lowest quintile of GI, those who were in the highest quintile had a 49% greater risk for lung cancer, with a 92% higher risk of developing squamous cell carcinoma of the lung - which accounts for around 25-30% of lung cancers.
The researchers did find a less significant association between a high-GI diet and increased risk of adenocarcinoma - which accounts for around 40% of lung cancers.
Looking at the results by education, the team found that participants in the highest GI quintile who had less than 12 years of education were 55% more likely to develop lung cancer than those in the lowest quintile.
Lung cancer risk remained higher for never-smokers on a high-GI diet
Among subjects who had never smoked - smoking is a leading cause of lung cancer - the researchers found that those in the highest GI quintile were more than twice as likely to develop lung cancer than those in the lowest quintile.
For most subjects, high GL did not raise lung cancer risk. For never-smokers, however, those in the highest quintile of GL were found to have an 81% greater risk of lung cancer, compared with those in the lowest GL quintile.
Commenting on the findings, Dr. Wu says:
"Although smoking is a major, well-characterized risk factor for lung cancer, it does not account for all the variations in lung cancer risk. This study provides additional evidence that diet may independently, and jointly with other risk factors, impact lung cancer etiology.
The results from this study suggest that, besides maintaining healthy lifestyles, reducing the consumption of foods and beverages with high glycemic index may serve as a means to lower the risk of lung cancer."
While the authors are unable to pinpoint exactly why a high-GI diet may raise lung cancer risk, they suggest it could be down to the higher levels of blood glucose and insulin that occur with high-GI foods, increasing the likelihood of glucose intolerance and insulin resistance.
They explain that previous research has linked insulin resistance to alterations in the insulin-like growth factors in the body, which are involved in cancer-related cell proliferation and differentiation.
The team admits that there are some limitations to the study. For example, GI and GL calculations were based on participants' self-reported food intakes, which may have contained errors.
Still, they say their findings warrant further investigation, noting that future studies should look at whether the association between GI and lung cancer is present in other racial and ethnic groups.
"[...] if the results from this study are confirmed, health care providers should be made aware of the link between glycemic index and lung cancer so they can communicate with their patients and the public about dietary changes for lung cancer prevention," says Dr. Wu.
Medical News Today recently reported on a study that suggests type 1 diabetes may increase the risk for certain cancers but lower the risk for others.