For the past few weeks, we’ve been writing about current research on ovarian cancer. Unfortunately, research has yet to uncover much that we can do in our daily lives to significantly minimize our risk of ovarian cancer. For example, a study that tracked 82,000 women for 24 years graded their diets to see which of them were eating a “healthy” diet, an “alternative healthy” diet, a Mediterranean diet, or an unhealthy, American-type diet. They then correlated the different healthy diets with the risk of ovarian cancer, but didn’t find that any particular dietary pattern reduced ovarian cancer risk (however, it should be noted that a previous study did suggest that cruciferous vegetables moderately decrease risk, though the decrease is not dramatic).
However, some interesting information has recently come to light about carbohydrates and ovarian cancer risk. A study published in July suggests that specific carbohydrates may actually decrease ovarian cancer risk. This study grouped data from 75 reports to determine whether diets that had high glycemic index or high glycemic load might increase risk of different cancers.
What are glycemic index and glycemic load, and why might they be important in cancer risk?
The glycemic index (GI) ranks foods according to how quickly they raise your blood glucose levels when you eat them. Foods with low GI values (under 55 according to the University of Sydney in Australia, where much research on GI has been conducted) raise blood sugar more slowly than high GI carbohydrates. This results in a slower rise in insulin levels as well. Insulin is a known cancer promoter; it raises levels of insulin-like growth factor-1 (IGF-1). Just as its name says, this growth factor promotes growth – and one of the types of growth it promotes is that of cancer cells. Glucose is the standard for a high GI food – its GI is 100. Foods that contain a lot of glucose will have a high GI, as will easily digested carbs, such as cornflakes (93), white rice (89) and baked potato (111, even higher than glucose!). Hummus, on the other hand, has a GI of 6, soybeans are 15 and peanuts are 7.
The glycemic load (GL) ranks foods according to two factors: the GI of the food, and how much carbohydrate the food contains. A low GL is less than 10. A medium GL is between 11 and 19, and a high GL is 20 or over. Most high GI foods that are easily digested will also have a high GL. But there are some surprises. Watermelon has a GI of 72, but its GL is only 4, since much of it is water, which doesn’t affect your glucose at all. Couscous has a GI of 65, but a GL of only 9. The internet has lots of information on GI and GL, and it’s easy to find charts of these values for common foods. While we don’t think that GI and GL are the only or even the best way to classify foods or to figure out what to eat, they do provide valuable information.
And in the case of cancer, the recent data indicates that they may offer a moderately good guide to what to eat to help reduce ovarian cancer risk. The paper published in July found that women who had diets with the highest GI and GL were 11% and 19% more likely to develop ovarian cancer than those whose diets had the lowest GIs and GLs.
We can see relationships to other findings from this latest data. Eating a high GI or high GL diet can promote weight gain and obesity. Women who are obese are 27% more likely to get ovarian cancer in the premenopausal period, and 38% more likely when they are postmenopausal, according to a 2014 paper that combined results from 19 studies. An Australian paper from 2011 that compared diets of 1366 women with ovarian cancer and 1414 women without ovarian cancer found that GL, though not GI or carbohydrate intake, was associated with a 24% increase in ovarian cancer risk, and that this risk was more pronounced in obese and overweight women, who are more prone to having high insulin levels.
Epidemiologists usually characterize increases in risk of around 20% as moderate. What does this mean? For comparison, think about the recent finding of increased breast cancer risk due to alcohol consumption. Two to three alcoholic drinks increases risk of breast cancer by 20%. This is certainly something to watch out for, especially since alcohol – unlike food – is not essential for life. But this is nowhere near the increase in risk of lung cancer for smokers. People who smoke have a risk for lung cancer that is 25 times higher than that of those who have never smoked, not 25% higher. Smoking causes a very high increase in lung cancer risk.
You can do without smoking and alcohol. But you can’t do without food. And carbohydrates (complex carbohydrates, to be clear) are a necessary part of a nutritious diet, the paleo craze notwithstanding. Carbohydrates are, among other things, a critical fuel for your brain! But you can make wise choices about the carbs that you eat. Avoiding fast-digesting, high-carb foods, and concentrating on high-fiber grain products such as rye breads or whole-wheat tortillas, along with fruits, vegetables (especially cruciferous vegetables), proteins and healthy nuts and oils will keep your glycemic index and glycemic load low. It’s one way to help reduce ovarian cancer risk – and your risk for other cancers as well.