Citric acid: what it actually does in the body

Metabolite Encyclopedia › Energy metabolism

Citric acid is the first thing made by the cycle that extracts energy from nearly everything you eat. It is also why lemons taste sour and why a great deal of packaged food stays stable on a shelf.

Also calledCitrate
Made inEvery mitochondrion you have
The cycle is named for itKrebs cycle
Industrially made byA mold, Aspergillus niger

Three things worth knowing

The world's citric acid does not come from lemons. Essentially all commercial citric acid is produced by feeding sugar to the mold Aspergillus niger. That process was scaled up industrially in the 1920s and ended Italy's long hold on the citrus-derived supply. The sour note in a soft drink was grown by a fungus.

It carries fat out of the mitochondrion. When energy is plentiful, citrate does not stay in the cycle. It is exported to the surrounding cytoplasm and split back apart to supply the carbon for building new fatty acids. The cycle's first molecule doubles as construction material.

It is a signal, not only a step. How much citrate is around tells the cell whether to keep breaking down sugar. High citrate inhibits one of the committing enzymes of glucose breakdown. The pathway reads its own output and slows itself down.

Citrate sits at a fork. Stay in the cycle and it becomes energy. Leave, and it becomes the carbon skeleton of a new fat.

The cycle itself

The cycle is named for the molecule at the top, which is the first thing it makes and the first thing it hands on.

Where you meet it in food

Lemons
Limes
Oranges
Tomatoes
Strawberries
Most sodas

On an ingredient label it is usually there as an acidity regulator or preservative rather than as a nutrient. Your own cells make far more of it than any food delivers.

The honest part: citric acid has no established relationship to sleep, and we are not going to manufacture one. It is in this encyclopedia for two reasons. It was quantified in the elixirs, and it happens to be one of the most central molecules in human metabolism, which makes it worth understanding on its own terms.

Questions people actually ask

Is the citric acid in food the same as the one in your cells?

Chemically, yes, the same molecule. The difference is scale and purpose. Your mitochondria cycle through enormous amounts of it continuously, while the amount in a food is small and is there for taste or stability.

What is the Krebs cycle?

The series of reactions that takes acetyl-CoA, derived from carbohydrate, fat or protein, and strips the energy out of it. Citrate is the first intermediate, which is why the cycle carries its name.

Is citric acid in soda bad for teeth?

Acids of any kind soften tooth enamel, which is why dentists talk about acidic drinks generally rather than citric acid specifically. That is a dental question, not a metabolic one.

Why is it in a mushroom encyclopedia?

It appears in AHARA's metabolomic map of its Reishi and Lion's Mane elixirs, which is how it ended up here.

Citric acid is one of more than 2,000 metabolites AHARA mapped across its Reishi and Lion's Mane elixirs. You can browse the rest of what is in the bottle.

Open the Metabolite Encyclopedia

References
Akram M. Citric acid cycle and role of its intermediates in metabolism. Cell Biochem Biophys. 2014;68(3):475-478. doi:10.1007/s12013-013-9750-1
Martínez-Reyes I, Chandel NS. Mitochondrial TCA cycle metabolites control physiology and disease. Nat Commun. 2020;11(1):102. doi:10.1038/s41467-019-13668-3

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