A lack of which substance can lead to an increase in edema?

The correct answer is the lack of protein or albumin. Albumin, a type of protein found in the blood, plays a crucial role in maintaining oncotic pressure, which is the force that keeps fluid within the blood vessels. When there is an insufficient amount of albumin in the bloodstream, this pressure decreases, allowing fluid to leak into the surrounding tissues. This leakage results in edema, which is the swelling caused by the accumulation of excess fluid in the interstitial spaces.

In contexts such as liver disease, nephrotic syndrome, or malnutrition, albumin levels can drop, subsequently leading to an increase in fluid accumulation in tissues and thus promoting edema. This mechanism highlights the importance of proteins in fluid balance and homeostasis within the body.