Increased consumption of carbohydrate-rich foods, especially starches, may boost the risk of breast cancer recurrence, new research finds.
Researcher Jennifer Emond, a public health doctoral student at the University of California, San Diego, looked at changes in the amount of carbohydrates, particularly starchy foods such as potatoes, that breast cancer survivors ate over a one-year period. Then she tracked the number of recurrences.
"Women who increased their carbohydrates and particularly their starch intake had a greater risk of recurrence than the women who decreased [it]," she said.
A link between a high-carb diet and a higher breast cancer risk has been reported before, but this new study focused particularly on starchy carbs, said Emond. She was scheduled to present the findings this week at the 2011 San Antonio Breast Cancer Conference.
Carbohydrates provide needed nutrients and energy, but some carbs are healthier than others. Refined carbohydrates, such as white breads and white pasta, contain more starch than whole grains. "We didn't pinpoint the exact foods," Emond said.
Emond looked at a subset of women who participated in the Women's Healthy Eating and Living Dietary Intervention Trial, which evaluated the effects of a plant-based diet for breast cancer survivors.
She divided the roughly 2,650 women into four groups, based on lowest to highest carbohydrate intake. She found that cancer recurred in 9.7% of those who decreased starch consumption the most compared with 14.2% of those with the biggest increase in starch consumption.
The women reported their carb intake at the start of the study and a year later. Carbohydrate intake was about 233 g a day at the study's start. Those whose cancer recurred had an average increase in carbohydrates of 2.3 g a day. Those who did not see a recurrence had an average decrease of 2.7 g of starch a day.
Elevated insulin levels
Changes in starch consumption were behind nearly half the carbohydrate intake change, she found. Those whose cancer did not return decreased starch intake by 8.7 g a day, while those with a recurrence decreased starch by only 4.1 g a day, she said.
According to the US Department of Agriculture, one slice of bread has 12.5 g of carbohydrate, of which 10 grams are starch. A cup of pasta has 43 g of carbs, 36 of which are starch.
Emond said she cannot explain the link between starch and breast cancer recurrence with certainty. However, starchy foods boost insulin levels, and elevated insulin levels have been linked with higher breast cancer risk, she said. The insulin may stimulate the growth of tumour cells, she explained.
The increased risk with higher starch intake held even when weight changes were taken into account, Emond said. Obesity and breast cancer have long been linked.
Marji McCullough, strategic director of nutritional epidemiology for the American Cancer Society, said the findings are noteworthy. "This is an important area of research because women who have been diagnosed with breast cancer want to know how to lower their risk of recurrence," she said.
But it's too soon to advise making any dietary changes, McCullough said. "Dietary recommendations change when several studies show the same thing," she said.
Breast cancer recurrence risk
The effect of diet on breast cancer recurrence risk is much less clear than the data on the importance of maintaining a healthy body weight, she said.
"The American Cancer Society recommends that breast cancer survivors strive to achieve and maintain a healthy weight through a mostly plant-based, varied diet and regular physical activity," McCullough said.
Emond agreed it's too soon to make new diet recommendations. However, she suggested women follow the 2010 Dietary Guidelines for Americans, which recommend limiting foods and beverages with added sugars that contribute to starch intake, she said.
In a second study involving diet and breast cancer, researchers found that following a low-carbohydrate diet just two days a week produced more significant weight loss than a standard low-calorie diet followed daily. People following the intermittent diet for four months lost an average of 9 pounds while the other dieters lost an average of 5 pounds, the British researchers found.
The two-day-a-week low-carb plan was also better than the daily diet at lowering blood levels of insulin, the researchers said. McCullough called that finding ''intriguing."
Because this research was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.