Diets delivering a sugar kick appear to increase breast cancer risk


Consuming a diet with a high glycemic index or glycemic load may increase the risk of breast cancer, according to results of the NutriNet-Santé cohort study.

Previous research in this cohort implicated consumption of sugar and sugary drinks as risk factors for cancer, noted Charlotte Debras, a PhD student at Inserm, University of Paris 13 in Bobigny, France.

“The mechanisms involved could be elevated postprandial glucose and insulin levels and insulin resistance, as well as diabetes and obesity,” she said.

To further explore the underlying mechanisms, Ms. Debras and colleagues looked at the glycemic index (a ranking of foods from 1 to 100 based on how they affect blood glucose levels) and glycemic load (the amount of carbohydrates ingested multiplied by the glycemic index of the food) in this cohort. The team assessed the relationship between glycemic measures and cancers overall as well as breast cancer in particular.

Charlotte Debras
The researchers evaluated 103,020 patients – 81,256 of them women – who had a mean age of 42 years and did not have cancer or diabetes at baseline.

The patients completed online questionnaires every 6 months that included three 24-hour dietary records, as well as questions about sociodemographics, lifestyle factors, health status, and physical activity. The dietary records were used to calculate glycemic index and glycemic load.

Ms. Debras reported the results of this research at the 2020 San Antonio Breast Cancer Symposium (abstract GS2-07).

Study results

The patients’ mean total carbohydrate intake was 198.4 g/day, their mean sugar intake was 92.8 g/day, their mean dietary glycemic index was 50.7, and their mean dietary glycemic load was 101.2 g/day.

The main contributors to dietary glycemic load were bread (27%), sugary items such as cakes and breakfast cereals (25%), and starch-based and processed savory dishes such as pizza (13%).

At a median follow-up of 7.7 years, 927 patients had received a breast cancer diagnosis and 3,131 had received any cancer diagnosis.

To assess associations between cancer and dietary glycemic index or glycemic load, the researchers performed multivariate analyses comparing the fifth and first quintiles for glycemic measures.

They found that higher dietary glycemic load was significantly associated with an increased risk of cancer overall (hazard ratio, 1.25; P = .0008) and postmenopausal breast cancer (HR, 1.64; P = .03).

Patients had an increased risk of any cancer (HR, 1.21; P = .002) and breast cancer (HR, 1.34; P = .04) if their diets had a higher contribution of medium- or high-glycemic-index foods to caloric intake. A medium/high glycemic index is a value greater than 55.

Patients had an increased risk of any cancer (HR, 1.27; P = .0001) and breast cancer (HR, 1.48; P = .002) if their diets had a higher contribution of medium-/high-glycemic-index foods to carbohydrate intake.

In stratified analyses, the association between breast cancer and the caloric intake measure was significant only for postmenopausal breast cancer. The association with the carbohydrate intake measure was significant for both premenopausal and postmenopausal breast cancer.

Patients had reduced overall cancer risk if their diets had a higher contribution of low-glycemic-index foods to carbohydrate intake (HR, 0.80; P = .0006) or caloric intake (HR, 0.83; P = .005).

Patients had reduced breast cancer risk if their diets had a higher contribution of low-glycemic-index foods to carbohydrate intake (HR, 0.74; P = .02). After stratification, this association was significant only for postmenopausal breast cancer.

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The researchers are conducting additional analyses to look at risks for specific breast cancer subtypes and at markers of inflammation in the cohort, according to Ms. Debras.

“A potential mechanism [for the observed associations] is weight gain, but other mechanisms are probably involved, including inflammation, oxidative stress, and increased insulin levels,” she proposed.

Next steps

“These results need to be replicated and confirmed in other large-scale cohort studies, and the underlying mechanisms need to be clarified by experimental data, but eventually, glycemic index and glycemic load may represent modifiable risk factors for primary cancer prevention,” Ms. Debras said. “This could be integrated in our diets every day since there are already some people who are following a low-glycemic-index diet – people with insulin resistance or diabetes.”

Furthermore, she noted, certain popular diets with higher fiber content and more whole-grain foods, such as the Mediterranean diet, also have a lower glycemic index.

“Dietary modification to lower glycemic load is a viable option for broad-scale [cancer] prevention,” agreed invited discussant Marian L. Neuhouser, PhD, of Fred Hutchinson Cancer Research Center in Seattle. “There are several consumer-facing tools to evaluate the glycemic index of foods. Probably the most well-known one is from Australia.”

Dr. Neuhouser went on to say that there are “sufficient observational data” to support associations between higher glycemic load diets and higher breast cancer risk.

“So what should be the next steps?” she asked. “Often, a randomized, controlled trial is the next step, but long-term dietary modification trials are very expensive and logistically challenging. They require tens of thousands of participants.”

A good alternative may be to pair with precision nutrition initiatives under development that seek to tailor dietary guidance to individual needs, Dr. Neuhouser proposed.

Dr. Marian L. Neuhouser

The study was funded by the Ministère de la Santé, Santé Publique France, Institut National de la Santé et de la Recherche Médicale, Institut National de la Recherche Agronomique, Conservatoire National des Arts et Métiers, and Sorbonne Paris Nord University. Ms. Debras disclosed no conflicts of interest. Dr. Neuhouser disclosed grant/research support from institutes within the National Institutes of Health.

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