Ongoing Community-Based Whole-Food, Plant-Based Lifestyle Effectively Preserves Muscle Mass during Body Mass Loss

Body fat and muscle mass showed opposing associations with mortality. The results of research on the effectiveness of popular body mass (BM) loss diets in obese subjects showed 20 to 30% loss of muscle mass within the total BM loss; conversely, when the subjects used a whole-food, plant-based (WFPB) diet, the loss was up to 42%. Therefore, we suggest an improvement. The aim of this retrospective analysis of data was to examine the assessment of changes in the body composition of 217 participants from all over Slovenia who joined our ongoing, community-based WFPB lifestyle programme from 2016 to 2021 and underwent two successive measurements of medically approved bioelectrical impedance. The WFPB lifestyle programme consisted of (i) nutrition, (ii) physical activity (PA) and (iii) a support system. The primary outcomes included the (vector of) change of body fat mass (BFM) per body height (BH), fat-free mass (FFM) per BH and whole-body phase angle (PhA) from the initial values to the first follow-up (FU) of the whole sample and for both sexes. Further, we examined the FFM change within the total BM loss according to their BMI classification and depending on how much BM they lost (5 kg < BM ≥ 5 kg) within the FU time (103.6 ± 89.8 day). Participants experienced a decrease in BFM per BH (−0.02 ± 0.02 kg/cm, p < 0.001), no change in FFM and an increase in PhA (0.2 ± 0.7°, p < 0.001). Importantly, the participants in the obesity BMI class achieved only partial FFM preservation (−1.5 ± 3.6 kg, p = 0.032 of FFM loss (20%) within −7.5 ± 6.1 kg, p < 0.001 of BM loss). However, the participants who lost BM < 5 kg had a significantly increased FFM (0.8 ± 3.2 kg, p = 0.001 of FFM (57%) within −1.4 ± 1.8 kg, p < 0.001 of BM loss), whereas the participants who lost BM ≥ 5 kg experienced a decrease in FFM (−2.2 ± 3.9 kg, p < 0.001 of FFM (−25%) within −8.8 ± 5.2 kg, p < 0.001 of BM loss). To conclude, the WFPB lifestyle, on average, effectively preserved FFM during BM and/or BFM loss among the normal and pre-obesity BMI classes but only partially among the obese BMI class and those who lost ≥ 5 kg of BM. Importantly, a customized PA strategy is needed for obese BMI class participants, where general resistance training is not possible or safe in order to preserve their muscle mass more effectively. In addition, muscle mass preservation is important for further improvements of BM, body composition and visual body image.