Which simplification is most correct when using the energy balance equation for short-term predictions (days to a few weeks)?

Energy balance is useless short-term because water fluctuations completely mask any caloric effects and invalidate the equation.

Energy balance gives exact weight change even in the short term because metabolic adaptation does not begin until months have passed.

Using daily intake minus daily expenditure approximates short-term weight change reasonably well, though body composition shifts and water changes may occur.

Short-term predictions require only measuring BMR; activity and intake can be ignored for periods under one month.