Final answer:
Excessive plasma protein decreases fluid loss through capillaries by increasing the blood's osmotic pressure, drawing more water back into the blood vessels.
Step-by-step explanation:
Excessive protein in the blood plasma will decrease the loss of fluid through the capillaries. This process is primarily influenced by the osmotic pressure in the capillaries, which is determined by the concentration of solutes such as proteins. Plasma proteins, particularly albumin, exert a significant osmotic force known as colloid osmotic pressure or oncotic pressure, which draws water into the bloodstream and helps maintain blood volume and pressure. When plasma protein levels are high, the osmotic pressure in the blood vessels increases, drawing more water back into the capillaries and thus reducing fluid loss into the tissue spaces.