First Middle East study finds significant association between glycaemic index and breast cancer

15-Dec-2021 - Last updated on 15-Dec-2021 at 02:41 GMT

Past studies especially in developed countries have reported inconsistent results on the role of GI and GL on the risk of breast cancer. It is known at the GI can increase blood glucose and insulin concentrations, which is also said to be associated to the amount, type and digestibility of carbohydrate consumed, which is quantified by GL. ©Getty Images

A significant association was found between dietary glycaemic index (GI) and risk of breast cancer, but not glycaemic load (GL), according to the ‘first’ study in Iran to examine carbohydrate quality with the onset of the disease.

The Middle East is a huge consumer of refined carbohydrates, so this study aimed to examine the relation between GI, GL, carbohydrate quality index (CQI) with the odds of breast cancer among women in a case-control study.

“According to our knowledge, there was no study with large sample size in Middle East in this regard. Due to different dietary pattern in Middle East, conducting research to find out this relationship is necessary in this region,” researchers from Tehran University of Medical Sciences wrote in Nutrition Journal.

Study design

This study recruited Iranian women aged 19 to 80 years old between 2014 and 2016. A total of 461 women with breast cancer diagnosed within the previous year, and 495 women without breast cancer were enrolled.

A validated food-frequency questionnaire was used to assess dietary intake over the previous year.

From the data, researchers were able to calculate GI, GL and carbohydrate quality index. Carbohydrate quality was determined as the ratio of solid carbohydrates to total carbohydrates, dietary fiber intake, GI and the ratio of whole grains to total grains.

Mean GI and GL of participants were 57.5 ± 7.2 and 245.7 ± 64.7 respectively.

GI is directly associated

Results revealed how individuals in the highest quartile of GI were 1.41 times more likely to have breast cancer than those in the lowest quartile for the whole population. For premenopausal women, those in the highest quartile of GI were 1.85 times higher likely to have breast cancer than those in the lowest quartile.

“The suggested mechanism is high insulinemia that resulted in high glyceamic diets, may inhibit apoptosis and synthesis of IGF binding proteins which promotes cellular proliferation,” researchers explained.

However, no significant association was observed between GL and breast cancer risk in the whole population.

For carbohydrate quality index (CQI), women in the highest quartile of CQI had significantly lower risk of breast cancer than those in the lowest quartile, among all participants and those in the premenopausal stage.

“We found no significant association between carbohydrate quality and odds of breast cancer in postmenopausal women.”

Recent discussion recommend that fibre and whole grain should be considered for carbohydrate quality.

“A high fibre diet provides many health benefits including weight loss, lower cholesterol levels, and decrease insulin resistance. In addition, fibre can reduce circulating estrogen levels by changing the gut microbiota which affect the reactivation of conjugated estrogens.”

“Therefore, the CQI that consider fibre, GI, solid or liquid form of carbohydrate and whole or refined grains seems to be better index for assessment.”

One of the explanations for the role of CQI in decreasing risk of cancers is through its anti-inflammatory properties.

“Whole grains are rich in antioxidants which are major elements of antioxidants enzymes activities and have been inversely linked to breast cancer risk. So, whole grains have phytoestrogens and polyphenols which have antioxidant properties and potential to inhibit cell multiplication and angiogenesis and to consequence cell apoptosis.”

Researchers added: “To our knowledge, this case-control study is among the first investigation that reports the association between total carbohydrates, GI, GL and CQI with odds of breast cancer with large sample size in a Middle Eastern country.”

“So, considering the carbohydrate type intake might be important for cancer control in society.”

One of the limitations of this study was its case-control design which cannot infer causality. prospective cohort studies are needed to examine the association of carbohydrate quality and risk of breast cancer, especially between pre- and post-menopausal women.

Source: Nutrition Journal

https://doi.org/10.1186/s12937-021-00752-y

“Dietary carbohydrate quality and risk of breast cancer among women”

Authors: Bahareh Sasanfar, et al.