Cancer link offers another reason to avoid highly processed carbs

In the new study, regular consumption of sugary beverages was associated with a 3 times greater risk of prostate cancer and higher intake of processed lunch foods such as pizza, burgers and meat sandwiches doubled prostate cancer risk. By contrast, healthy carbohydrate-containing foods like legumes, non-starchy vegetables, fruits and whole grains were collectively associated with a 67 percent lower risk for breast cancer.

"One of the most important findings here is that the type of carbohydrate-containing foods you consume can impact your cancer risk," said Nour Makarem, a Ph.D. student at New York University and the study's lead author. "It appears that healthy carbohydrate sources, such as legumes, tend to protect us from cancer, but non-healthy ones, such as fast foods and sugary beverages, seem to increase the risk of these cancers."

Makarem will present the research at the American Society for Nutrition Scientific Sessions and Annual Meeting during Experimental Biology 2016.

The study is based on the health records of 3,100 volunteers tracked since the early 1970s. Researchers began tracking participants' diets through detailed food frequency questionnaires starting in 1991. For the new study, Makarem and her colleagues categorized all of the study participants' food sources by glycemic index -- a measure of dietary carbohydrate quality based on an item's relative impact on blood sugar levels as compared to a reference food -- and glycemic load, a measure of both the quantity and quality of carbohydrates in a given food item. They then analyzed the results in relation to volunteers' cancer rates.

After taking into account multiple cancer risk factors, the study found that eating foods with a higher glycemic load was associated with an 88 percent higher prostate cancer risk. Prostate cancer is one of the most common types of cancer and the second leading cause of cancer-related death in men.

"Our study showed very strong associations between certain foods and cancer, in particular with prostate cancer," said Makarem. "There had not been very many studies on food sources and prostate cancer previously."

The risk increase was most pronounced for people who regularly consumed processed lunch foods or sugary beverages, a category that includes sugar-sweetened soft drinks in addition to fruit juices, which can be naturally high in sugar and often contain added sugars.

"Americans consume almost half of their added sugars in beverages," said Makarem. "Sugar-sweetened beverages have been shown to increase the risk of obesity and diabetes, and our study documents that they may also have a detrimental impact on cancer risk."

By contrast, consuming low-glycemic index foods such as legumes, non-starchy vegetables, most fruits and whole grains was associated with a 67 percent lower breast cancer risk. Breast cancer risk was also reduced among women who had a higher level of carbohydrate intake overall as a proportion of their total calories. However, in this study participants with in the highest level of carbohydrate intake also had higher intakes of fruits and vegetables, whole grains and legumes. These findings underscore the idea that the type of carbohydrates matters more than the total amount of carbohydrates, said Makarem.

Among individual foods, legumes such as beans, lentils and peas were associated with 32 percent lower risk of all overweight- and obesity-related cancers, including breast, prostate and colorectal cancers.

By nature of the study design, the results point only to associations, not necessarily to cause-and-effect. Nonetheless, the findings are in line with previous studies, which have shown that malignant cancer cells seem to feed on sugar, and that diets high in refined carbohydrates may lead to a range of adverse health effects primarily due to their impacts on body fatness and on the dysregulation of insulin and glucose, both of which are factors that may increase cancer risk.

"Current cancer prevention guidelines recommend avoiding sugary drinks and limiting the consumption of energy-dense foods, which tend to be high in refined carbohydrates," said Makarem. "I think our findings add to the body of evidence behind this recommendation and strengthen the associations between these types of food and cancer."

One caveat that Makarem noted is that the volunteers involved in the study were 99 percent Caucasian. Further study is needed to determine if these associations hold true in more ethnically-diverse groups.

Makarem will present the findings during the Experimental Biology 2016 meeting on Tuesday, April 5.