Effect of Low-Fat Diet on Depression Score in Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Clinical Trials

Abstract Context Current evidence on the effect of a low-fat (LF) diet on depression scores has been inconsistent. Objective To explore the effect of an LF diet on depression scores of adults by systematic review and meta-analysis of randomized controlled trials (RCTs). Data Sources The PubMed, ISI Web of Science, Scopus, and CENTRAL databases were searched from inception to June 7, 2023, to identify trials investigating the effect of an LF diet (fat intake ≤30% of energy intake) on the depression score. Data Extraction Random-effects meta-analyses were used to estimate pooled summary effects of an LF diet on the depression score (as Hedges g). Data Analysis Finding from 10 trials with 50 846 participants indicated no significant change in depression score following LF diets in comparison with usual diet (Hedges g = −0.11; 95% CI, −0.25 to 0.03; P = 0.12; I2 = 70.7% [for I2, 95% CI, 44%, 85%]). However, a significant improvement was observed in both usual diet and LF diets when the content of protein was 15-20% of calorie intake (LF, normal protein diet: n = 5, Hedges g = −0.21, 95% CI, −0.24 to −0.01, P = 0.04, I2 = 0%; usual, normal protein diet: n = 3, Hedges g = −0.28, 95% CI, −0.51 to −0.05, P = 0.01, I2 = 0%). Sensitivity analysis also found the depression score improved following LF diet intervention in participants without baseline depression. Conclusion This study revealed that LF diet may have small beneficial effect on depression score in the studies enrolled mentally healthy participants. Moreover, achieving to adequate dietary protein is likely to be a better intervention than manipulating dietary fat to improve depression scores. However, it is not clear whether this effect will last in the long term. Conducting more studies may change the results due to the low-certainty of evidence. Systematic Review Registration CRD42023420978 (https://www.crd.york.ac.uk/PROSPERO).