Study hints at potential risk between unhealthy low-fat diets and postmenopausal breast cancer

A recent study published in the journal Nutrition examined the associations between low-fat diets (LFDs) and the risk of breast cancer.

Breast cancer is one of the most common cancers among females, representing one in four new cancer cases. Several factors can influence the risk of breast cancer, and some are modifiable, e.g., diet. Besides the genetic predisposition, hormonal and lifestyle factors are linked to the risk of breast cancer. Dietary factors account for 20%-60% of cancers globally and a third of cancer deaths in Western countries.

The women’s health initiative trial addressed the effect of low-fat dietary patterns with a higher intake of fruits, cereals, and vegetables. The incidence of breast cancer after over eight years of follow-up was 9% lower among the intervention arm. Besides, another study found that a dietary pattern with high-fat choices was associated with breast cancer. Further, recent studies have emphasized the distinction between less healthy and healthy LFDs.

Applied nutritional investigation: Associations between overall, healthful, and unhealthful low-fat dietary patterns and breast cancer risk in a Mediterranean cohort: The SUN project. Image Credit: Nadiia Loboda / Shutterstock

About the study

The present study investigated the association between different LFD patterns and breast cancer risk in a Mediterranean cohort. The cohort was established in 1999, and participants completed baseline and biennial follow-up questionnaires after enrolment. The researchers included females who enrolled before March 2017 and completed the food frequency questionnaire (FFQ) before December 2019.

Subjects with a history of breast cancer, menopause before 35 years, and implausible total energy intake were excluded. Diet was examined at baseline and 10 years later using the validated FFQ. Participants were stratified according to the percent energy from proteins, carbohydrates, and fat. For proteins and carbohydrates, the researchers assigned 10 and 0 points to participants in the highest and lowest categories (of adherence). A reverse scoring method was adopted for fats.

Accordingly, the team estimated overall LFD, healthful LFD, and unhealthful LFD scores. The healthful LFD score was based on the percent of energy from saturated fats, plant protein, and high-quality carbohydrates. The unhealthful LFD score was based on the percent of energy from animal protein, unsaturated fats, and low-quality carbohydrates. Additionally, adherence to LFDs was classified by menopausal status. The primary outcome of the study was breast cancer incidence.

Cox proportional hazard regression was used to estimate hazard ratios and 95% confidence intervals for the overall risk of breast cancer. In addition, breast cancer risk was assessed before and after menopause. Models were stratified by age and enrolment period. Multivariable-adjusted models were used after controlling for confounders. Repeated measurements were adjusted for using data from the FFQs after 10 years of follow-up.

Findings

The study included 10,930 females with an average age of 35.2. The overall LFD score was 0-12 and 19-30 points for the lowest and highest tertiles, respectively. The healthful LFD score was 0-11 and 20-30 points for the lowest and highest tertiles, respectively. The unhealthful LFD score was 0-13 points for the lowest and 18-30 points for the highest tertile.

Participants with higher overall or healthful LFD scores at baseline were older, more likely to be former or never smokers, consumed less alcohol, more likely to have an earlier age of menarche, and were more physically active. Further, among these participants, there was a higher proportion of hormone replacement therapy use.

By contrast, females with higher unhealthful LFD scores were older, had less energy intake from high-quality carbohydrates, less fat intake, lower alcohol intake, and had a high body mass index (BMI). Participants were followed up for a median of 12.1 years. The researchers identified 150 cases of breast cancer from 1999 to 2000. Overall, unhealthful and healthful LFD scores were not associated with overall breast cancer risk.

Results were similar for repeated measurements after 10 years of follow-up. When stratified by menopausal status, LFD scores were not associated with pre-menopausal breast cancer risk. Nonetheless, moderate adherence to unhealthful LFD was significantly associated with post-menopausal breast cancer risk, which was non-significant with repeated measurements.

Conclusions

In summary, the study did not find any associations between LFD patterns and the risk of breast cancer. Notably, moderate adherence to unhealthful LFD was significantly associated with the risk of breast cancer after menopause. However, this should be interpreted with caution given the low number of post-menopausal breast cancer cases and the lack of significance with repeated measurements. Future studies should explore the relationship between LFD scores and sub-types of breast cancer with larger samples and longer follow-up times.