Different sources of dietary fat may influence cancer risk in obesity

Obesity raises the risk of many cancers and makes it harder for immune cells to fight tumours. Until now, most studies focused on obesity rather than how much fat people eat and not what kind of fat. 

Findings from a decade-long international study reported in the current issue of the journal, Nature Metabolism has shown that the source of dietary fat can change how well key immune cells work in obesity. 

The research is led by Professor Lydia Lynch from the Ludwig Institute for Cancer Research and Princeton University with collaborators including Professor Helen Roche from UCD School of Public Health, Physiotherapy and Sports Science and Director, UCD Conway Institute. 

The team fed mice a high-fat diet (45% of calories from fat) made mostly from one of six sources: lard, beef tallow, butter, coconut oil, olive oil or palm oil. All diets caused equal weight gain. After 10 weeks, the mice received melanoma cancer cells under the skin. The diets continued while researchers tracked tumour growth and studied immune cell function inside the tumours.

The study reveals that not all fats are equal when it comes to cancer immunity in obesity. Animal fats (lard, beef tallow, butter) create blood metabolites that block immune cells from doing their job. This poor immune function caused faster tumour growth.  

In contrast, feeding plant fats (coconut, olive, palm oils) avoided these harmful byproducts and helped maintain stronger anti-tumour immune responses. Importantly, feeding plant derived fats did not speed up tumour growth despite resulting in the same level of obesity.  

“These findings highlight the significance of diet in maintaining a healthy immune system,” said Lynch. “More important, they indicate that modifications to fat in the diet may improve outcomes in obese people undergoing treatment for cancer and suggest such measures should be clinically evaluated as a potential dietary intervention for such patients.”

An estimated one billion people worldwide with obesity are at risk for a variety of obesity-related diseases, including cardiovascular disease and cancer.
Obesity is emerging as a significant risk factor for cancer because it reduces the robustness of our immune surveillance system. This system should clear unhealthy or cancerous cells. 

Professor Helen Roche added, “Our study clearly demonstrates that diet has a role in determining anti-tumour immunity in obesity. Future investigation must focus on how modulation of diet in humans alters the metabolic milieu, immune function and tumour outcomes to evaluate the potential for diet-based interventions to support successful cancer treatment.”

This study was supported by the Ludwig Institute for Cancer Research, the Mark Foundation, the U.S. National Institutes of Health, Research Ireland, the European Research Council, the Cancer Research Institute and the Landry Cancer Biology Consortium. Prof. Roche’s team were supported by Research Ireland.

The study is published in the July edition of Nature Metabolism and available online.

Journal citation: Kunkemoeller, B., Prendeville, H., McIntyre, C. et al. The source of dietary fat influences anti-tumour immunity in obese mice. Nat Metab (2025). https://doi.org/10.1038/s42255-025-01330-w