A growing body of evidence is showing a strong association between diet and breast cancer risk and survival, particularly high glycemic load and sugar intake. Two large population studies at the 2020 San Antonio Breast Cancer Symposium supported these observations.1,2
Findings from the Nurses’ Health Study and Nurses’ Health Study II linked reduced mortality risk among breast cancer survivors to greater adherence to a diet known to reduce the risk for type 2 diabetes.1 Investigators of the French NutriNet-Santé study examined the flip side and showed that diets high in glycemic load may increase the risk of developing breast cancer.2
Nurses’ Health Studies: Diabetes Risk-Reduction Diet
In a substudy of the large Nurses’ Health Study and Nurses’ Health Study II, greater adherence to the “diabetes risk-reduction diet” was linked to better survival after a breast cancer diagnosis.1 “Promoting dietary changes consistent with the prevention of type 2 diabetes may be important for breast cancer survivors,” said Tengteng Wang, PhD, MSPH, MBBS, a postdoctoral research fellow in the Channing Division of Network Medicine at Brigham and Women’s Hospital, Harvard Medical School, and Harvard T.H. Chan School of Public Health.
Type 2 diabetes is a risk factor for breast cancer and possibly also breast cancer–related mortality; a diagnosis of breast cancer also increases the likelihood of developing type 2 diabetes. “Identifying modifiable strategies to prevent type 2 diabetes among breast cancer survivors may be important to improve survival,” Dr. Wang said.
“Promoting dietary changes consistent with the prevention of type 2 diabetes may be important for breast cancer survivors.”— Tengteng Wang, PhD, MSPH, MBBS
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The analysis included 8,320 women with stage I to III breast cancer who participated in the Nurses’ Health Study and Nurses’ Health Study II. Participants provided updated information on diet and other covariates through questionnaires once every 2 to 4 years; researchers looked for associations between survival after breast cancer diagnosis and the cumulative average adherence to the diabetes risk-reduction diet after diagnosis. The diabetes risk-reduction diet is a scale with points (8–32) corresponding to each quartile of intake of several dietary factors. A higher score indicates a healthier overall diet.
The diabetes risk-reduction diet emphasizes higher intake of cereal fiber, coffee, nuts, whole fruits, and polyunsaturated fat (vs saturated fat) and lower intake of trans-fat, red meat, and sugar-sweetened beverages and fruit juices. In a previous analysis of the Nurses’ Health Study and Nurses’ Health Study II, the diabetes risk-reduction diet reduced the risk of type 2 diabetes by about 40%.3 The hypothesis for the current study was that a higher diabetes risk-reduction diet score after breast cancer diagnosis may be associated with better survival.
Women in the highest diabetes risk-reduction diet quintile vs the lowest had a higher median individual income, were more likely to have used postmenopausal hormone therapy, and were more likely to be physically active and lean, but the quintiles were similar with regard to mean age at diagnosis, race, and tumor and treatment characteristics.
At a median follow-up of 13 years since diagnosis, 2,146 women had died, including 948 due to breast cancer. The multivariate analysis showed that women with higher postdiagnosis cumulative average diabetes risk-reduction diet scores had a 13% nonsignificant lower risk for breast cancer–specific mortality (P = .13) and a 31% significantly lower risk for all-cause mortality (P < .0001), Dr. Wang reported.
Benefits were also provided by improving one’s diabetes risk-reduction diet score after a breast cancer diagnosis. Those moving from a lower to a higher category reduced their risk for breast cancer–specific death by 20% and their all-cause mortality risk by 14%, compared with women who consistently maintained lower scores before and after diagnosis. Those who kept a high diabetes risk-reduction diet score had an 18% lower risk for all-cause mortality. Findings remained consistent regardless of estrogen receptor status or disease stage.
“Our results do not support [the possibility] that the association between diet and better survival was mediated by weight change after a breast cancer diagnosis,” said Dr. Wang. Among deaths from all causes, ~250 were due to cardiovascular disease; various causes contributed to the remaining deaths.
As for presumed mechanisms of benefit, gene-expression profiles in tumors of a subgroup of patients showed that high diabetes risk-reduction diet scores were most associated with pathways related to immune regulation and cell proliferation.
Charlotte Debras, MSc
Mathilde Touvier, PhD
In the large prospective French NutriNet-Santé cohort of 103,020 participants (81,256 men and 21,494 men), consumption of a diet with a high-glycemic load was associated with higher risk for postmenopausal breast cancer, according to Charlotte Debras, MSc, and Mathilde Touvier, PhD, of the Nutritional Epidemiology Research Team (Inserm/Inrae/Cnam/Sorbonne Paris Nord Universit).2
“Greater consumption of sugar, added sugars, and sugary food and beverages was associated with an increased risk of breast cancer, especially before menopause,”4 Ms. Debras said. If replicated in other large populations, the findings suggest “that sugar and sugary foods, whose consumption is increasing in Western countries, may potentially represent a modifiable risk factor for breast cancer prevention.”
“Greater consumption of sugar, added sugars, and sugary food and beverages was associated with an increased risk of breast cancer, especially before menopause.”— Charlotte Debras, MSc
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In the NutriNet-Santé study, which opened in 2009, participants answered online questionnaires every 6 months about sociodemographic and lifestyle factors, physical activity, and diet. Cancer cases that developed within the cohort were validated and linked to national medical databases and the national mortality registry.
The researchers evaluated participants’ glycemic index (which defines the hyperglycemic power of a food and compares carbohydrate foods) and glycemic load (which corresponds to the amount of carbohydrates ingested, multiplied by the glycemic index of the food, taking into account both the quantity and quality of food consumed). Sweet foods and beverages have a high glycemic index.
High Glycemic Load Associated With Increased Cancer Risk
According to the questionnaires, breads and sugary foods contributed 53% to the mean dietary glycemic load of the respondents. Of 103,020, who were followed for a median of 7.7 years, 3,131 patients developed cancer, and 924 of these cases were breast cancer.
Significant associations were shown between diet and cancer risk (most exposed quintile 5 vs less exposed quintile):
Ms. Debras and her colleagues next plan to analyze the results according to specific subtypes of breast cancer. Both Dr. Wang and Ms. Debras cautioned that their study results may not be extrapolatable beyond the study populations and that they require validation.
DISCLOSURE: Dr. Wang and Ms. Debras and Dr. Touvier reported no conflicts of interest.
1. Wang T, Farvid M, Kang JH, et al: Diabetes risk reduction diet and survival following breast cancer. 2020 San Antonio Breast Cancer Symposium. Abstract GS2-09. Presented December 9, 2020.
2. Debras C, Chazelas E, Srour B, et al: Glycemic index, glycemic load and breast cancer risk: Results from the prospective NutriNet-Santé cohort. 2020 San Antonio Breast Cancer Symposium. Abstract GS2-07. Presented December 9, 2020.
3. Rhee JJ, Mattei J, Hughes MD, et al: Dietary diabetes risk reduction score, race and ethnicity, and risk of type 2 diabetes in women. Diabetes Care 38:596-603, 2015.
4. Debras C, Chazelas E, Srour B, et al: Total and added sugar intakes, sugar types, and cancer risk: Results from the prospective NutriNet-Santé cohort. Am J Clin Nutr 112:1267-1279, 2020.
Neil M. Iyengar, MD, Assistant Attending Physician at Memorial Sloan Kettering Cancer Center, New York, has researched the links between breast cancer and lifestyle. He provided comments on these two abstracts from the 2020 San Antonio Breast Cancer Symposium (SABCS) for The ASCO Post.