Why do astronauts excrete out substantially higher amount of calcium in therir urine as they go to space? Please tell me if the composition of urine changes depending on the food consumed.If so, please give examples.

In space, there is no gravitational force acting on the body of the astronauts. Without the effects of gravity, skeletal muscle is no longer required to maintain posture. In a weightless environment, astronauts put almost no weight on the back muscles or leg muscles used for standing up. Those muscles then start to weaken and eventually get smaller. Consequently, some muscles atrophy rapidly, and without regular exercise astronauts can lose up to 20% of their muscle mass in just 5 to 11 days. This results in extensive bone loss and associated increased calcium levels in the urine. The astronauts face an increased risk of developing kidney stones, due to decreased urine output, urine acidity, and increased calcium excretion as a result of bone loss.

The composition of urine changes depending on the diet we consume.

• A high-protein diet facilitates greater production of urine volume. The increase of urea in the body requires more filtration by the kidneys. This means that more water is pulled from the blood to compensate for urea removal. Excessive urination while following a high-protein diet can lead to dehydration.
• Increased protein consumption leads to increased calcium in the urine. Excessive calcium is associated with a loss in bone mineral density and an increase in osteoporotic conditions, especially in the elderly.