No Differences in Muscular Adaptations to Long-Term Resistance Training Between Young Strict Vegetarian and Non-Vegetarian Women.

Some evidence suggests that strict vegetarian and non-vegetarian diets may influence muscular adaptations to resistance training (RT), but findings remain inconsistent. This study compared muscular and body composition adaptations in strict vegetarian (VEG) and non-vegetarian (NV) women following a 16-week RT program without protein supplementation. Twenty-five VEG (28.7 ± 4.6 years) and 20 NV (30.9 ± 6.5 years) trained twice per week while maintaining their usual diets. Pre- and post-intervention assessments included thigh and calf muscle thickness (MT) via ultrasonography, composite maximal strength (knee extensor, knee flexor, and plantar flexor 1-RM), and whole-body composition assessed by DXA. Dietary intake was monitored throughout the intervention. Both groups showed significant increases in thigh MT (VEG: 81.2 ± 9.9 to 85.6 ± 9.6 mm; NV: 80.8 ± 9.9 to 87.3 ± 9.6 mm; all p < 0.001) and in composite maximal strength (VEG 106.9 ± 21.3 to 132.6 ± 21.6 kg; NV 107.9 ± 21.3 to 133.1 ± 21.8 kg; all p < 0.001), with no differences between groups. Thigh lean soft tissue (LST) increased significantly in both groups (p < 0.001), while calf LST, gastrocnemius medialis MT, total fat mass, and bone mass remained unchanged (all p > 0.05). VEG consumed significantly less protein (1.0 ± 0.3 g/kg) than NV (1.3 ± 0.3 g/kg; p = 0.002), yet no between-group differences were observed in muscle hypertrophy or strength gains. Despite lower protein consumption in the VEG group, no differences in muscle size and maximum strength adaptations were observed between strict vegetarian and non-vegetarian women after a long-term RT program. Trial Registration: This study was also registered at Clinical Trials (NCT05576337).