While the laws of thermodynamics state that matter cannot be created or destroyed, in the mummification process, bodies are capable of losing mass through several ways. One way is in the beginnings of the mummification process itself, where internal organs were removed. While the total weight of internal organs varies, it's generally around 20 pounds, or 9.07 kilograms. Another way the body loses mass in mummification is through the dehydration of bodily tissue through the application of salt to the mummy, both internally and externally. Humans average around 60% of their total body weight being composed of water. Through completely effective, which is nearly impossible, total dehydration of the body would leave only around 40% of the body's initial mass present, (0.4(remaining mass))(200kg)=80 kg, but that is nearly impossible without highly sophisticated instruments with exceptional climate control. However, this dehydration would also decrease a mummy's mass greatly.