People who eat a sugary, starchy diet may be raising their risk of lung cancer, even if they don't smoke, researchers say.
They found that people who recall eating more foods that have a high glycemic index also were more likely to develop lung cancer. Glycemic index is a term that's familiar to people with diabetes. It describes food that raises blood sugar and stimulates production of insulin — think bagels, white rice and some fruits such as melon and pineapple.
It's not the first study to link glycemic index with cancer risk, but it's rare to link it with lung cancer. That may be mostly because lung cancer is so overwhelmingly caused by smoking.
The team at MD Anderson Cancer Center in Houston studied 1,905 people who had just been diagnosed with lung cancer and compared them to 2,415 people without cancer. They quizzed them about their eating habits, smoking, income and other factors.
People who ate the most foods with a high glycemic index were about 50 percent more likely to be in the lung cancer group than people who reported they ate the fewest high-glycemic foods, the team reported in the journal Cancer Epidemiology and Biomarkers.
The link was stronger among people who never smoked; non-smokers were more than twice as likely to have lung cancer if they reported eating a high-glycemic diet.
"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," said Dr. Xifeng Wu, who led the study.
How can this happen? Doctors aren't sure, but there's a theory that high-glycemic foods stimulate the body to make insulin, which in turn affects the growth of cells via compounds called insulin-like growth factors or IGF. Cancer is the uncontrolled proliferation of cells, so it might be that the high-glycemic foods are fueling the growth of tiny tumors.
"IGFs have been shown to play a critical role in regulating cell proliferation and differentiation in cancer and there is evidence to suggest that IGFs are elevated in lung cancer patients," Wu's team wrote.
It's a suspect in several types of cancer.
"Previous studies have investigated the association between glycemic index, and the related measure glycemic load, and a variety of cancers including colorectal, stomach, pancreas, endometrial, ovarian, prostate, and thyroid but these studies are limited and results have been largely inconclusive," the researchers wrote.
This study is not conclusive, either. For one thing, the researchers asked their volunteers to remember what they ate. For another, it's an association. People who eat high-glycemic foods may also do something else that also raises their risk of cancer. And this particular study focused only on non-Hispanic white people.
Marji McCullough, an expert in nutritional epidemiology at the American Cancer Society, says it will be important to look at people who don't have cancer now and watch what they eat for years or decades, and see who develops cancer.
Lung cancer is the No. 1 cancer killer in the U.S., killing more than 150,000 people a year. It causes only vague symptoms at first, so when most people are diagnosed, the cancer has already spread and is then far more likely to be fatal.
Experts know diet and lifestyle can affect cancer. Obesity, lack of exercise, eating red meat and lots of high-fat dairy foods, and eating too few fruits and vegetables can all raise a person's odds of developing cancer.
This study adds to a growing body of evidence that people can lower their cancer risk not only by staying away from tobacco and exercising more, but by choosing a healthier diet.
"Aside from not smoking, it's important to follow cancer prevention guidelines that maintain healthy body weight, physical activity, and eating an overall healthy diet rich in vegetables and plant food and lower red and processed meat. Choose foods that help maintain healthy body weight," McCullough said.
According to the American Diabetes Association, low-glycemic foods include:
- 100 percent stone-ground whole wheat or pumpernickel bread
- Oatmeal (rolled or steel-cut), oat bran, muesli
- Pasta, converted rice, barley, bulgar
- Sweet potato, corn, yam, lima/butter beans, peas, legumes and lentils
- Most fruits, non-starchy vegetables and carrots
Medium glycemic index foods include:
- Whole wheat, rye and pita bread
- Quick oats
- Brown, wild or basmati rice, couscous
High glycemic index foods include:
- White bread, including bagels
- Corn flakes, puffed rice, bran flakes, instant oatmeal
- Shortgrain white rice, rice pasta, macaroni and cheese from mix
- Russet potato, pumpkin
- Pretzels, rice cakes, popcorn, saltine crackers
- melons and pineapple