High glycemic index diet may increase lung cancer risk

A study led by researchers at The University of Texas MD Anderson Cancer Center revealed an association between a high glycemic index diet and increased risk for lung cancer in non-Hispanic white individuals.

Researchers assessed the association between lung cancer and quintiles of glycemic load or glycemic index among 1,905 patients with newly diagnosed disease and 2,413 healthy controls.

Xifeng Wu

The investigators observed a significant association between glycemic index and lung cancer risk among those in the highest quintile compared with those in the lowest quintile (OR = 1.49; 95% CI, 1.21-1.83; P for trend < .001).

The association between glycemic index and lung cancer risk appeared more pronounced among those who never smoked (5th quintile vs. 1st quintile, OR = 2.25; 95% CI, 1.42-3.57), those with squamous cell carcinomas (5th quintile vs. 1st quintile, OR = 1.92; 95% CI, 1.3-2.83) and those with fewer than 12 years of education (5th quintile vs. 1st quintile; OR = 1.75; 95% CI, 1.19-2.58, P for interaction = 0.02).

Study researcher Xifeng Wu, MD, PhD, professor of epidemiology at MD Anderson, spoke with HemOnc Today about the findings and their potential impact.

Question: Can you explain the association between high glycemic index and lung cancer?

Answer: Our study showed that a diet high in glycemic index may increase lung cancer risk. The glycemic index is a ranking (ie, 0-100) of foods based on how quickly they raise blood sugar levels given an equal amount of the digestible carbohydrates in each food. The ability of each food to raise blood sugar levels is compared with that of a test food typically glucose, or table sugar which is assigned the number 100. Foods with higher glycemic index raise blood sugar levels more quickly than foods with lower glycemic index. The overall glycemic index reflects the average quality of carbohydrates consumed. Examples of foods and beverages with high glycemic indexes ( 70) include white bread or bagels, corn flakes, puffed rice, bran flakes, instant oatmeal, short grain, white rice, rice pasta, macaroni, cheese from a mix, russet potatoes, pumpkin, pretzels, rice cakes, popcorn, saltine crackers, melons, pineapple, and some energy or sports drinks.

Q: What prompted your study?

A: Although smoking is the most well-characterized risk factor for lung cancer, it does not account for all variations in lung cancer risk. Lung cancer still occurs among never smokers. Accumulating evidence suggests that selected dietary factors may modulate lung cancer risk. Diets high in glycemic index result in higher levels of blood glucose and insulin, which promote glucose intolerance, insulin resistance, hyperinsulinemia and perturbations in the insulin-like growth factors (IGF) axis. Previous studies, including one study from my group, suggested that higher plasma levels of IGFs and lower levels of IGF-binding proteins were associated with an increased risk for lung cancer. Given the connection of glycemic index, IGF axis and lung cancer risk, we decided to take a look at the association between dietary glycemic index and glycemic load and lung cancer risk.

Q: Were you surprised by the results?

A: I was slightly surprised by the results that only glycemic index, not glycemic load, was associated with lung cancer risk. This suggests that it is the average quality, instead of quantity, of carbohydrate consumed that may modulate lung cancer risk.

Q: L ung cancer incidence has increased among never smokers in the United States . What role does diet play?

A: There are multiple factors that could contribute to this increase, including lack of physical activity, low consumption of fruits and nonstarchy vegetables, and a high consumption of red meat, processed meat, total fat and butter. Consumption of glucose-rich foods can be a major factor, but multiple factors play into this risk. More research is needed to understand the underlying reason and form a conclusion.

Q: What areas must be addressed in future research ?

A: I would recommend validating the results in prospective cohort studies. If validated, then testing whether a low glycemic index can reduce lung cancer risk in trials is warranted. If the relationship is confirmed to be causal, we should investigate the mechanisms underlying the causal relationship and subsequently develop interventions. We are looking at whether glycemic index is associated with clinical outcomes in patients with lung cancer.

Q: Given your study results, what prevention measures would you recommend?

A: I would recommend limiting the consumption of foods and beverages with high glycemic indexes as a general health tip for more balanced diet, as well as to lower the risks for lung cancer and other chronic diseases, such as diabetes. It is also important to be aware that lung cancer is caused by multiple factors. In order to reduce the risk for lung cancer, one needs to take an integrative approach. One can do this by not smoking, eating less red meat, exercising, and consuming more fruits and vegetables.

Q: Is there anything else that you feel is important to add?

A: We showed in our study that patients with lung cancer are more likely to have a high glycemic index diet compared with healthy controls. In our study, we investigated an individual’s overall dietary glycemic index. However, we did not investigate individual foods (eg, bagels or white rice), so we cannot draw any conclusion regarding each individual food. Also, our study showed an association between a high glycemic index diet and lung cancer risk, which is not equal to a causal relationship. – by Jennifer Southall

For more information:

Xifeng Wu, MD, PhD, can be reached at The University of Texas MD Anderson Cancer Center, Main Building, 1515 Holcombe Blvd., Houston, Texas 77030; email: xwu@mdanderson.org.

Reference:

Melkonian SC, et al. Cancer Epidemiol Biomarkers Prev. 2016; doi:10.1158/1055-9965.EPI-15-0765.

Disclosure: Wu reports no relevant financial disclosures.