Background: The influence of diverse dietary patterns on fat-free mass (FFM) in people with overweight or obesity, beyond individual dietary components, remains underexplored.
Aim: To synthesise evidence from observational studies on the association between various dietary patterns and FFM in adults from general populations with overweight or obesity.
Methods: We systematically searched Embase, Medline, Web of Science, and Google Scholar for observational studies published in English (-June 2024). Pooled effect estimates were calculated using the standardised mean difference (SMD) with 95% confidence intervals (95%CIs) in random-effects meta-analyses. Subgroup analyses and heterogeneity statistics (I2, Q, and τ2) were also employed.
Results: From 3,381 initial records, 47 studies were included in the systematic review and 20 in the meta-analysis. Healthy dietary patterns showed no overall significant association with combined measures of FFM (-0.14[-0.36,-0.08]; I2=78.7%, τ2=0.07, Q=40.73, p<0.001). However, FFM measured in kilograms showed a significant negative association (-0.23[-0.38,-0.09]; I2=41.1%, τ2=0.01, Q=8.03, p=0.15), particularly in advanced economies. Neutral dietary patterns also showed no significant association (-0.31[-0.67, 0.04]; I2=99.5%, τ2=0.52 Q=518.72, p<0.001), though FFM percentage showed a negative association (-1.40[-2.59,-0.20]; I2=99.4%, τ2=0.42, Q=339.94, p<0.001). Notably, protein intake within neutral patterns showed a significant negative association with FFM (-0.54[-1.07,-0.01]; I2=96.2%, τ2=0.26, Q=137.29, p<0.001) and in advanced economies. Unhealthy dietary patterns had no overall significant association with FFM (0.08[0.18,0.34]; I2=88.2%, τ2=0.09, Q=50.56, p<0.001), but a significant negative association was observed in studies that included both working-age (18–64) and older adults (>65) (-0.09[-0.17,-0.01]; I2=0.0%; τ2=0.00, Q=2.20, p=0.53). High heterogeneity was observed across many analyses.
Conclusion: The relationship between dietary patterns and FFM in people with overweight or obesity is complex. While overall associations were often non-significant, specific healthy dietary patterns and, interestingly, higher protein intake showed some negative associations with FFM in certain subgroups. Unhealthy patterns generally lacked significant associations. Further research is needed to understand these relationships and the sources of heterogeneity.