There is a long history of controlling diets before missions, and providing very specific foods for these missions to not upset the stomach. See an MRE from the

There is a long history of controlling diets before missions, and providing very specific foods for these missions to not upset the stomach. See an MRE from the U-2: https://www.youtube.com/watch?v=LZuEGAsO4CA https://www.youtube.com/watch?v=LZuEGAsO4CA