What role do proteins play in maintaining the body’s fluid balance?

Proteins play a crucial role in maintaining the body's fluid balance primarily through the regulation of osmotic pressure in the bloodstream. They are involved in the synthesis of various plasma proteins, such as albumin, which help to hold water in the blood vessels. This action prevents fluid from leaking into surrounding tissues, which could lead to edema, a condition characterized by swelling. By maintaining proper osmotic pressure, proteins help to ensure that fluids are distributed appropriately between different compartments of the body, including vascular, interstitial, and intracellular spaces. Additionally, proteins are essential for maintaining acid-base balance by acting as buffers in the blood, supporting the body's pH levels amidst various metabolic processes. Thus, the integral role of proteins in regulating fluid and acid-base balance confirms this choice as the correct answer.