What would be the best explanation for Mrs. Lenzo's 4-pound weight gain over two days?

A 4-pound weight gain over just two days is most commonly associated with changes in body fluid rather than with changes in body fat or other factors. This rapid increase in weight is typically indicative of fluid retention, which can occur for various reasons, such as diet, medications, or underlying medical conditions.

During brief periods, fluctuations in body weight can often occur due to changes in hydration status rather than significant changes in body mass. For example, a high salt intake can lead to the body retaining more water, resulting in noticeable weight gain. Similarly, certain medications or medical issues like heart failure or kidney dysfunction can lead to edema, contributing to fluid retention.

While factors like overeating or clothing changes may influence weight measurements, they cannot account for such a rapid change as this. Therefore, attributing Mrs. Lenzo's weight gain to body fluid is the most accurate and clinically relevant explanation.