Which of the following increases solute concentration in the blood?

A high sodium intake increases solute concentration in the blood because it directly contributes to the overall osmolarity of the blood. When sodium levels rise, they create an osmotic gradient that leads to the retention of water in the bloodstream, increasing the concentration of solutes. Sodium is a crucial electrolyte, and its presence in higher amounts can draw water into the bloodstream, thereby elevating the concentration of other solutes as well, such as glucose and urea.

On the other hand, excessive drinking of water would dilute solute concentration in the blood, potentially leading to a condition known as hyponatremia, where sodium levels are abnormally low. A low protein diet would decrease the levels of proteins in the blood, which are significant solutes, thus potentially reducing overall solute concentration. Increased fiber intake generally affects digestion and does not directly impact blood solute concentration in the same way that high sodium intake does.