Could dairy processing help explain inconsistent findings on dairy consumption and breast cancer risk?

The relationship between dairy consumption and breast cancer risk has raised questions for scientists for years, with various studies reporting differing results. Recent work has begun to explore whether these inconsistent findings could be explained by the degree of food processing.

Although nutritional composition (such as the amount of calcium, fat, vitamin D or hormones in a product) has traditionally been considered the primary factor for explaining these inconsistent results, emerging laboratory and food chemistry research suggests that processing methods may also influence the biological properties of dairy foods.

A new review paper, published recently in the journal Advances in Nutrition, led by researchers at the University of Toulouse, aims to move the research beyond a nutrient-only explanation for the differences in association and asks whether food-processing chemistry should be built into future study designs.

Dr Silia Ayadi, first author on the paper, has been funded by the Wereld Kanker Onderzoek Fonds, (WKOF) – the Netherlands-based charity within the World Cancer Research Fund network of charities.

Dr Silia Ayadi, Ph.D., said:

“Through this work we have proposed a novel hypothesis linking the processing of dairy products to the formation of molecules that may influence breast cancer-related pathways.

“By combining research from nutritional epidemiology, food chemistry, and molecular mechanisms, this review paper provides a new potential perspective for explaining the differences we see in the existing research that has examined the dairy and breast cancer association.”

What does the evidence say so far?

When exploring how diet and nutrition can impact cancer risk, dairy products have received considerable attention due to their complex composition, which includes macronutrients, hormones, and a wide range of bioactive lipids. Bioactive lipids are compounds that regulate biological processes within the body, such as inflammation or cell growth.

To date, studies examining a possible link between dairy consumption and breast cancer have found inconsistent results, with reports of neutral, inverse, or positive associations depending on the population, tumour type, and type of dairy product consumed.

Milk, fermented products, cheeses, and highly processed dairy foods differ not only in fat content and fermentation status, but also in their exposure to technological processes such as heating, drying, and storage. Recent laboratory research suggests that these processing methods can generate a wide range of bioactive molecules beyond conventional nutrients, some of which may affect biological pathways, even at very low levels.

Proposing a new framework

To dig further into the existing literature, the authors integrated findings from 82 publications covering three areas of research – studies on dairy consumption and breast cancer, research on food chemistry, and lab studies on how these changes might affect cancer-related pathways.

A central hypothesis is that processing dairy products can generate or modify bioactive fat-derived molecules, including oxidised forms of cholesterol. In experimental models, some of these compounds can influence biological pathways relevant to breast cancer, including inflammation and hormone signalling. The review also notes that fermentation may generate metabolites with potentially different, possibly protective, biological effects.

This work proposes an original framework suggesting that dairy processing, not only nutrient composition, may help explain the differing results seen in this area of breast cancer research. The team highlights that the evidence is mainly from laboratory and mechanistic and epidemiological research and is not sufficient to draw conclusions about cause and effect, or steer clinical advice.

Dr Marc Poirot, Ph.D., Research Director at Inserm, said:

“Different dairy products, including milk, cheese, yoghurt, butter, fermented products and ultra-processed dairy foods, undergo different forms of heating, fermentation, storage and industrial processing, which may change their molecular composition.

“By integrating nutritional epidemiology, food chemistry, and molecular biology, this work offers a novel angle to explain the differences in the associations observed across dairy products and cancer outcomes.”

World Cancer Research Fund International Assistant Director of Policy and Research Dr Helen Croker, said:

“The WCRF network’s evidence syntheses have shown suggestive protective effects of dairy foods and high calcium diets, but the findings are not conclusive. The current work outlines the heterogeneity of dairy foods, including the level of processing, and may help to explain previous inconclusive findings.

“The focus on processing is interesting and in line with emerging research on ultra-processed foods. This represents a promising avenue for advancing our understanding of how processing of dairy foods could influence the development of cancer.”