A pharmacist's perspective on health and metabolic disease
A new study has shown that consuming foods with a high glycaemic index (GI) increases your risk of developing lung cancer. But it is what you eat, not how many carbs you consume (Glycaemic load or “GL”) that is important. While I haven’t been able to access the full article, the abstract and bits gleaned from online newspapers makes interesting reading.
Simply put, this study found that eating significant amounts of foods with a high GI such as bread, sugar, honey, rice, breakfast cereals, and potato increases your risk of developing lung cancer. The risk was highest in those who had never smoked, and in those who hadn’t finished a full high school education.
The authors suggest (via NZ Herald) that this may be caused by these high GI foods causing hyperinsulinaemia which causes an increase in insulin-like growth factor (IGF-1), which enhances cellular growth and proliferation. So if you have some cancerous cells around, IGF-1 will encourage growth. While this is a major factor for cancer, especially for lung cancer, there is more to the story as I wrote previously. High GI foods cause high glucose levels, the combination of high insulin and high glucose causes an increase in reactive oxidative species, which can cause deranged DNA and impair repair mechanisms. The high glucose levels also encourages cellular growth and proliferation, especially cancer cells as they only use glucose for energy (Warburg effect).
While this study only looked at lung cancer, I strongly believe that high GI foods will be implicated with far more cancers, especially since having diabetes is a risk factor for many cancers including breast, colon, and liver. Interestingly, having diabetes is not associated with an increased risk of lung cancer, but I suspect this association will change with the long-term reduction in cigarette smoking and the increase in diabetes.
Although the NZ Herald reports the overall carbohydrate quantity consumed didn’t increase cancer risk, I’m not sure that is actually the case. The interesting thing about glycaemic load is that it is based on a ratio of the number of carbs in a serving compared to the GI. Foods that are low in carbohydrate (e.g. most vegetables) will have a low GL, even if they have a high GI. High GL foods will always have a high GI. Sweetened beverages, and almost all processed foods, including pasta (normally a low GI food) all have a high GL.
This means that if these people all ate the same amounts of carbohydrates over the day, those who ate a low GI diet must have been eating far more of the high fibrous veggies and fruits, like broccoli, cauliflower, berries. Diets rich in these foods have been shown to decrease the risk of cancers. Whether this is due to the increased fibre, or other micronutrients that are not present in other foods is unknown. From experience it is very difficult to eat a significant amount of carbohydrates if you are sticking to low GL foods, so I still believe that while carbohydrate is critical, carb quantity is also important.
Maybe I will change my mind on the quality/quantity aspects after I have read the full-text article.
The impact of glycaemic load will also differ depending on your hyperinsulinaemia status, but more on that next time.
Chettouh, H., Lequoy, M., Fartoux, L., Vigouroux, C., & Desbois-Mouthon, C. (2015). Hyperinsulinaemia and insulin signalling in the pathogenesis and the clinical course of hepatocellular carcinoma. Liver International, 35(10), 2203-2217. doi:10.1111/liv.12903
Giovannucci, E. (1995). Insulin and colon cancer. Cancer Causes & Control, 6, 164-179.
Giovannucci, E., Harlan, D. M., Archer, M. C., Bergenstal, R. M., Gapstur, S. M., Habel, L. A., . . . Yee, D. (2010). Diabetes and cancer: A consensus report. CA: A Cancer Journal for Clinicians, 60(4), 207-221. doi:10.3322/caac.20078
Melkonian, S. C., Daniel, C. R., Ye, Y., Pierzynski, J. A., Roth, J. A., & Wu, X. (2016). Glycemic Index, Glycemic Load, and Lung Cancer Risk in Non-Hispanic Whites. Cancer Epidemiology Biomarkers & Prevention, 25(3), 532-539.