Final answer:
A common reason for weight gain between dialysis treatments is fluid retention, often due to excessive sodium reabsorption in the renal tubes because of increased water reabsorption in the kidneys.
Step-by-step explanation:
A common reason for weight gain between dialysis treatments is fluid retention. This occurs primarily due to excessive sodium reabsorption by renal tubes, which can be driven by mechanisms like increased water reabsorption in the kidneys. Consequently, when there is higher sodium in the body, it attracts more water, thus leading to fluid accumulation and weight gain. This ties in with the concept of decreased aldosterone secretion leading to decreased sodium reabsorption and therefore less water retention, which would be the opposite effect of what is commonly observed in this scenario.