Can reduced calorie intake (and weight loss) help reduce breast cancer risk? The answer is unclear, but as Joseph Sparano, MD, Vice Chairman of Medical Oncology, Montefiore Einstein Center for Cancer Care and Associate Director for Clinical Research at Albert Einstein Cancer Center in the Bronx, New York, puts it, "There may be a role for dietary and lifestyle interventions in reducing the risk of breast cancer and breast cancer recurrence."

The Big Idea

The theory behind calorie restriction for breast cancer prevention and treatment is based on several studies showing that obesity and lack of regular physical activity are risk factors for breast cancer in postmenopausal women. Additionally, obese women who have been diagnosed with estrogen receptor-positive breast cancer—which accounts for about two-thirds of all breast cancer cases—have poorer outcomes than non-obese women.

"There’s something about obesity that contributes to developing breast cancer or having a reoccurrence if already diagnosed," Sparano says. "These factors may include inflammation, high levels of certain types of cholesterol, insulin, or estrogen—or maybe a combination of these factors."

"The association is especially convincing for recurrence of estrogen receptor-positive breast cancer, which starts to play out about three years after diagnosis." However, "This should provide sufficient time for lifestyle interventions to have an impact," he adds.

Scientists believe that lifestyle factors like obesity and lack of exercise raise our risk of cancer because they increase the amount of certain types of nutrients and hormones circulating in our blood stream, which may—directly or indirectly—control cancer cell growth. According to one study, in the US, 14% of cancer deaths in men and 20% in women are attributable to excess weight.

The theory is also based on the understanding that, like healthy cells, cancer cells need a steady supply of nutrients to grow. These nutrients come from the food we eat, like the complex carbohydrates our bodies ultimately digest as glucose (sugar). Although glucose provides energy for the body, in excess it can also cause tumor cells to multiply.

Data also shows that most breast cancer patients gain weight during treatment, which can contribute to worse outcomes.

Current Research

Researchers are investigating the benefits of different types of calorie-restricted diets. Although a long-term study recently concluded that calorie restriction did not result in improved survival in monkeys, in 2006, the Women’s Health Initiative Study demonstrated that a low fat diet reduced the incidence of invasive breast cancer. Meanwhile, researchers at Duke University have launched a clinical trial on the benefits of a ketogenic diet (one that’s low in carbohydrates, provides adequate protein, and is high in fat) in breast cancer patients. And at Thomas Jefferson University, scientists are looking at reducing calories by 25 percent in early stage breast cancer patients who are undergoing radiation therapy; the researchers suggest that fewer calories may help shrink tumors and enhance the effectiveness of radiation.

With regard to the different diets studied, while it’s "not clear what diet is optimal, in studies, low carb diets are associated with the most weight loss, and the most sustained weight loss," when compared with low fat and Mediterranean diets, Sparano notes. "There’s an interest in a low carb diet because it seems to be more effective in lowering insulin levels, and insulin acts fuel for cancer cells—obese people tend to have higher insulin levels and more insulin resistance." Insulin is a hormone released by the pancreas; it helps cells use energy from food. Insulin resistance means the body is not using the hormone efficiently; it can leads to several serious health problems.

At Montefiore, Sparano is currently working on a study of 30-40 patients with "potentially curable" breast cancer. "Patients are being put on a low carb diet prior to removal of breast cancer tumor removal," he says. "The study will and measure the effects of diet," including whether the diet seems to induce cancer cell death.

Reducing Risk

"For women with a normal BMI (18.5-25), there’s no real need to do anything other than maintain a healthy lifestyle," Sparano says. "For women with a BMI of more than 30 (obesity), implementing some changes in their diet and lifestyle would seem prudent. It may reduce their risk of cancer occurrence and have secondary benefits in terms of reducing the risk of developing hypertension, diabetes, arthritis, and other complications, or improving control of those conditions if they already exist." Even modest degrees of exercise and dietary changes can produce profound metabolic changes, which, if sustained, could add up—and benefit those who are overweight (with BMIs between 25 and 30), he added.

So while research to date only shows an association between calorie restriction and cancer outcomes, not cause and effect, in the future, scientists may be able to demonstrate the benefit of diet modifications in minimizing cancer cell growth and disease progression.

Joseph Sparano, MD, and Renee Stubbins, RD, (a registered dietician at Houston Methodist Cancer Center) reviewed this article.


Joseph Sparano, MD, Vice Chairman of Medical Oncology, Montefiore Einstein Center for Cancer Care and Associate Director for Clinical Research at Albert Einstein Cancer Center in the Bronx. 

Renee Stubbins, RD, Houston Methodist Cancer Center.

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