Numerous studies have investigated the associations between high glycemic index/load diets and breast cancer risk, with somewhat inconsistent results. Some studies have found an association between such diets and breast cancer risk only for some breast cancer types or according to menopausal status. Nevertheless, based on the available evidence, diets with high glycemic load appear to increase the risk of breast cancer even in women who are not overweight.
Diets with abundant high glycemic index foods have high glycemic load
The glycemic index ranks foods based on their immediate effect on blood glucose (blood sugar)levels. Glucose itself has a ranking of 100 and other foods are ranked in relation to it based on their influence on blood sugar. Diets dominated by high glycemic index foods have a high glycemic load. Glycemic load is calculated by multiplying the glycemic index, carbohydrate content, and intake frequency of individual foods. In studies measuring glycemic index and glycemic load, glycemic index values typically are assigned to foods consumed based on published figures. Glycemic load is then calculated by multiplying the carbohydrate content and intake frequency of individual foods consumed by their glycemic index.
A small piece of sugar candy has a high glycemic index but a low glycemic load. A bag of the candy will have a high glycemic load in addition to having a high glycemic index. Common high glycemic foods include sweetened breakfast cereals, white rice, white potatoes, pancakes, granola, oatmeal, white bread, fried ripe plantains, sweet potatoes, molasses, sugar and candy and cake and sweet desserts.
High glycemic index/load diets and breast cancer risk
Studies of the influence of glycemic index and glycemic load on breast cancer risk have not always found an association. There are obvious problems with assessing dietary intake that make it difficult to generate valid results. Retrospective studies in particular are subject to unintentional recall bias on the part of participants. In addition, it is difficult to separate the glycemic index from other nutritional characteristics of food that influence breast cancer risk. Nevertheless, attempts continue to be made to study this question because it is plausible that a high glycemic diet could increase breast cancer risk through its influence on blood glucose and insulin levels, sex hormones, and insulin-like growth factor 1 (IGF-1).
High glycemic diet and menopausal status
Several prospective studies that have examined the association have reported contradictory results as to whether a high glycemic diet is more closely linked to breast cancer risk before or after menopause:
- A 2012 study of Italian women in the European Prospective Investigation into Cancer and Nutrition (EPIC) who were followed for a median of 11 years reported that women in the highest quintile of glycemic load had 1.45 times the risk of breast cancer as those in the lowest quintile. The results did not vary according to menopausal status or body mass index.
- A Chinese study that included 74,942 women aged 40 to 70 years who were followed for an average 7.35 years reported that both high carbohydrate intake and glycemic load were associated with higher risk of breast cancer among women under 50.
- A Canadian study with 49,613 participants who were followed for a median of 16.6 years, found an association between glycemic index and breast cancer risk, but only among postmenopausal women. The association between glycemic index/glycemic load and risk in postmenopausal women was slightly stronger among normal-weight women.
- A study that included 8,926 Italian women who were followed for 11.5 years reported that both high glycemic index and high glycemic load diets were associated with higher risk of breast cancer. Total carbohydrate consumption was not found to be related to greater breast cancer risk, however high carbohydrate consumption from high-glycemic index foods was. When the women were divided into groups based on baseline menopausal status and body mass index (BMI), the increased risk of glycemic load was found to be restricted to those who were premenopausal, particularly those with normal BMI (below 25).
- A study that included 62,739 postmenopausal French women who were followed for nine years reported a positive association between glycemic index and breast cancer among overweight women and women with the highest waist circumference. There was also found to be an association between carbohydrate intake, glycemic load, and estrogen receptor-negative (ER-) breast cancer risk.
High glycemic diet and breast cancer type
Several other prospective studies, in addition to the French study above, have found an association between high glycemic diets and breast cancer risk by subtype:
- A 2012 study of 334,849 women in the European Prospective Investigation into Cancer and Nutrition (EPIC) study reported that diets with high glycemic load and carbohydrate intake were linked to an increased risk of developing ER- and ER-/PR- breast cancer among postmenopausal women.
- A study of 148,767 Women's Heath Initiative (WHI) participants who were followed for a median of eight years reported no associations overall between high glycemic diets and breast cancer. However, there was a trend toward significance for the positive association between glycemic load and noninvasive cancers (DCIS or LCIS).
- A study including 61,433 women in the Swedish Mammography Cohort who were followed for an average of 17.4 years reported that glycemic load but not carbohydrate intake or glycemic index was weakly positively associated with risk of breast cancer. When the data was analyzed by estrogen receptor (ER) and progesterone receptor (PR) status, significant positive associations of carbohydrate intake, glycemic index and glycemic load with risk of ER+/PR- breast cancer were found. No associations were observed for ER+/PR+ or ER-/PR- breast tumors.
- A Danish study of 23,870 postmenopausal Danish women found no associations for intake of glucose, fructose, sucrose, maltose, lactose, or starch and breast cancer risk, and no associations for glycemic index or glycemic load. A borderline significant positive association between glycemic index and ER- breast cancer was found.
Possible insulin connection
Although not all studies are in agreement, the finding of some studies that normal weight women might be more susceptible to high glycemic diets is interesting, in part because it is unexpected. Along with other studies that have found a higher risk of breast cancer among women who consume a lot of sweets or sweet desserts, this finding suggests that the frequent insulin spikes produced by habitual high glycemic index food consumption might contribute to breast cancer risk and should be avoided by those at high risk for breast cancer, as well as survivors.
Please see our article on how to optimize your breast cancer diet for information on what to eat during all stages of treatment and recovery. Below are links to recent studies on glycemic load. For a more complete list of studies, please click on the tag glycemic index/load.