Do people change their eating habits after a diagnosis of cancer? A systematic review

People who live with and beyond cancer are considered to be motivated to change their diet. However, there is a lack of reviews conducted on what specific dietary changes people make and further evaluation may inform future interventional studies. Hence, we aim to summarise the evidence on dietary changes in observational studies before and after a cancer diagnosis.

This systematic review followed the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analysis. Electronic searches were conducted in four databases to identify cohort and cross-sectional studies on dietary changes before and after a cancer diagnosis, excluding studies that evaluated an intervention. Quality assessment was undertaken, and meta-analyses were conducted where suitable.

We identified 14 studies with 16,443 participants diagnosed with cancer, with age range 18-75 years. Dietary change was assessed <1-5 years before diagnosis and up to 12 years post-diagnosis. Meta-analyses showed that the standard mean difference (SMD) for energy (SMD-0.32, 95% confidence interval = -0.46 to -0.17) and carbohydrate consumption (SMD 0.20, 95% confidence interval = -0.27 to -0.14). Studies showed inconsistent findings for fat, protein and fibre, most food groups, and supplement intake. A small decrease in red and processed meat consumption was consistently reported.

All studies reported some positive changes in dietary intake and supplement consumption after receiving a cancer diagnosis without any intervention. However, differences for food groups and nutrients were mainly small and not necessarily clinically meaningful. Evidence demonstrates that a cancer diagnosis alone is insufficient to motivate people to change their dietary intake, indicating that most people would benefit from a dietary intervention to facilitate change.