Effects of conjugated linoleic acid and endurance training on peripheral blood and bone marrow of trained mice

Fat supplements, especially conjugated linoleic acid (CLA), are increasingly popular ergogenic aids among endurance athletes. To evaluate the importance of fat supplementation in the practice of endurance sports, we investigated the effects of CLA supplementation on body weight, muscle hypertrophy, peripheral blood composition, and bone marrow composition in healthy, young, endurance-trained mice. Young, healthy mice were subdivided into control, trained, and treated groups, according to their running attitudes. Training was performed over a period of 6 weeks on a treadmill, at a gradually increasing duration and speed. CLA-treated groups were gavaged with 0.425 mg.d(-1) CLA supplement for the entire training period. The exercise protocol induced a significant decrease in body weight (p < 0.003) and a consistent muscle hypertrophy (p < 0.003). A morphological evaluation of bone marrow from trained mice revealed an accelerated turnover of the erythroid lineage, i.e., a relative increase in proerythroblasts. Conjugated linoleic acid supplementation did not induce a further decrease in total body weights in either untrained or trained mice (p = 0.747), but induced a further increase in muscle hypertrophy in trained mice (p = 0.009). Furthermore, CLA feeding induced an important lymphopenia in peripheral blood of CLA-fed trained mice (p <= 0.05). These findings suggest that CLA may improve the performance of endurance athletes by increasing muscle hypertrophy, and, at the same time, that it may cause oxidative stress damage, leading to a peripheral blood lymphopenia and a consequent neutrophilia as a defensive response. Despite the positive increase in muscle hypertrophy claimed by the pharmaceutics companies, we suggest that endurance athletes and those looking to improve their own skeletal muscle mass refrain from CLA supplementation, because it seems to intensify the oxidative stress caused by exhaustive exercise.