Evaluation of NASA Foodbars as a standard diet for use in Short-Term rodent space flight studies

Objectives A standard rodent diet for space flight must meet the unique conditions imposed by the space environment and must be nutritionally adequate because diet can influence the outcome of experiments. We evaluated the use of National Aeronautics and Space Administration (NASA) Foodbars as a standard space flight diet for rats. Methods The Foodbarʹs semi-purified formulation permitted criteria such as nutrient consistency, high nutrient bioavailability, and flexibility of formulation to be met. Extrusion of the semi-purified diet produced Foodbars with the proper texture and a non-crumbing solid form for use in space. Treatment of Foodbar with 0.1% potassium sorbate prevented mold growth. Irradiation (15 to 25 kGy) prevented bacterial growth and, in combination with sorbate treatment, added protection against mold for shelf stability. Results During the development process, nutrient analyses indicated that extrusion and irradiation produces nutrient losses. Nutrients were adjusted accordingly to compensate for processing losses. Nutrient analysis of Foodbars continues to be performed routinely to monitor nutrient levels. It is important that the standard rodent diet provide nutrients that will prevent deficiency but also avoid excess that may mask physiologic changes produced by space flight. All vitamin levels in the Foodbars, except for vitamin K, conformed to or exceeded the current National Research Council (NRC) 1995 recommendations. All indispensable amino acids in Foodbar conformed to or exceeded the NRC nutrient recommendation for mouse growth and rat maintenance. However, some indispensable amino acids were slightly below recommendations for rat reproduction and growth. Short-term (18 to 20 d) animal feeding studies indicated that Foodbars are palatable, support growth, and maintain health in rats. Conclusions Results indicated that NASA Rodent Foodbars meet the physical and nutritional criteria required to support rodents in the space environment and thus may be used successfully as a standard diet for short-term space flight studies. However, the nutritional adequacy of NASA Rodent Foodbars as a standard diet on longer-duration (>20 d) space flight missions remains to be determined.