Abstract
Does glucose oxidation yield 6 or 10 H
2
O? Debated 30 years ago and revived in 2025, the question underlies a brain metabolic water budget built on C
6
H
1
2
O
6
+ 6O
2
→ 6CO
2
+ 10H
2
O, which does not satisfy the law of conservation of mass. The balanced form, C
6
H
1
2
O
6
+ 6O
2
+ 4ADP
3
⁻ + 4HPO
4
2
⁻ + 4H⁺ → 6CO
2
+ 10H
2
O + 4ATP
4
⁻, combines combustion (6H
2
O) with substrate-level phosphorylation (4H
2
O). This reconciles both answers, resolving the controversy. How much water is secreted per glucose depends on the fate of ATP; choosing 6 or 10 changes estimates of brain metabolic water by two-thirds.