A soy-based supplement alters energy metabolism but not the exercise-induced stress response.

Objective: To determine the changes in endurance capacity as well as in metabolic, hormonal and inflammatory markers induced by endurance training combined with a soy,protein based supplement.

Design: Randomized controlled study consisting of moderate endurance training without (GO) or with (G1) a soy protein based supplement.

Subjects: Two groups of 15 subjects (10 males and 5 females in each group): healthy sports students aged 23.6 +/- 1.9 years.

Measurements: Body composition (body mass (BM), body density (BD) by air displacement) and physical fitness (determined by treadmill ergometry) were measured at baseline and after 6 weeks of the intervention; changes in circulating metabolic and hormonal parameters (glucose, lactate, urea, uric acid, ammonia, cortisol, insulin, IGF-1), and exercise-induced stress and inflammatory markers (CK, LDH, myoglobin, hs-CRP, IL-6, IL-10, blood cell counts) were determined after the intervention period in afield test (11.5 km running on hilly ground).

Results: 30 participants completed the 6-week study; 28 students were able to perform the field test. No significant changes in BM and BD were noted after intervention with only slight increases in running performance and maximum aerobic capacity in the total group (2%, p=0.016). Subjects in the G1 group showed significant improvements in running velocity and lower lactate values following the intervention (-12%, p=0,003). In addition, the G1 group showed significantly lower differences in the exercise-induced increase of metabolic parameters (triglycerides, uric acid) and insulin in the post-exercise recovery period.

Conclusions: Our data suggest that moderate endurance training in combination with a soy-based protein supplement improves aerobic energy supply and metabolic function in healthy sports students, even without changes in body composition and without changes in the exercise-induced stress and inflammatory reaction.