The effect of a space food bar diet on body and muscle mass in normal and hind-limb suspended rats

A food bar diet is used for rats in space flight. Since ground based studies have only been performed with the typical rat chow in dry pellet form, we tested whether the food bar diet allows normal growth and normal response of muscle protein content to unloading. These parameters were measured in normal and tail-cast hind limb suspended rats fed standard pellets or food bars. Body mass following 5 d of hind limb unloading was similar in bar-fed (97.9 ± 4.8 g) and pellet-fed (92.6 ± 3.4 g) animals (p > 0.05). In addition, gains in body mass were comparable between bar-fed (5.3 g/d) and pellet-fed (5.1 g/d) animals. Food bar consumption over 6 d incresed from 10.5 to 12.0 g/d animal. During 5 d of hind limb suspension, food bar consumption increased from 13.2 ± 1.4 to 19.1 ± 1.4 g/d per animal. In agreement with previous studies, hind limb unloading reduced soleus muscle mass and protein content per 100 g body mass in both diet groups (p < 0.05). Protein content per 100 g body mass was unchanged for the plantaris, extensor digitorum longus and tibialis anterior muscles during suspension in both diet groups. Rodent consumption of a food bar diet results in normal gains in body mass and muscle protein when compared to a standard pellet diet, and does not alter the atrophic response of skeletal muscle to unloading.