FNDC5 and prediabetes syndrome: Subgroup analyses by health status of participants revealed a significant change in irisin for patients with type 2 diabetes [0.00 (95 % CI, 0.00 to 0.01), p = 0.002; I2 = 0.0 %; six interventions] and prediabetes [-0.06 (95 % CI, -0.10 to -0.02), p = 0.002.