Many people know carbs are 4 kCal/g, protein is 4 kCal/g, and fat is 9 kCal/g.

Some people know that alcohol is 7 kCal/g

How many people know the energy content of citric acid? Citric acid is right there in the Krebs cycle (ATP cycle) so it must have energy content.

It is 2.5 kCal/g. Never listed on nutrition labels.