Dietary acid load and the risk of cancer: A systematic review and dose-response meta-analysis of observational studies

Aims Recent evidence suggests the link between adherence to an acidogenic diet and the risk of some types of cancers, such as colorectal and breast cancers. This systematic review and meta-analysis aimed to clarify the association between dietary acid load and cancer risk. Data search and synthesis Online databases (PubMed, Scopus, EMBASE, Scholar Google and ISI web of sciences) were searched between January 1990 and May 2021. The risk ratio (RR) was extracted from eligible studies and random-effects meta-analysis was performed to calculate pooled RR of studies. Nine studies (three cohorts, six case-control) were included. Higher dietary acid load scores [including potential renal acid load (PRAL) and net endogenous acid production (NEAP)] were associated with the increased risk of cancer [RRPRAL, 1.77; 95% confidence interval (CI), 1.27-2.46; n = 8; RRNEAP, 1.58, 95% CI: 1.20-2.09, n = 7). Dose-response analysis suggested that a 20-score increase in dietary PRAL and NEAP was associated with 27 and 8% higher risk of cancer, respectively (RRPRAL, 1.27; 95% CI, 1.02-1.60; nonlinearity P = 0.12; RRNEAP, 1.08; 95% CI, 1.02-1.13, nonlinearity P = 0.06). A significant positive relationship between dietary PRAL and risk of cancer was only observed in the subgroup of women. Associations were significant in both men and women for dietary NEAP. Subgroup analyses based on cancer type were only possible for breast cancer. There was no significant association between dietary acid load (PRAL and NEAP) and breast cancer risk. Conclusion Our analysis showed that high adherence to an acidogenic diet is associated with an increased risk of cancer. The protocol for this meta-analysis was registered in PROSPERO registration no. CRD42019146460.