What are GABA and theanine, and which foods have them?

GABA (gamma-aminobutyric acid) and theanine are both amino acids, but neither is one of the amino acids the body uses to build proteins. They come from different foods. GABA is found in germinated brown rice, tomatoes and some fermented foods: a Thai study found 585 mg per kg in germinated brown rice, about three times as much as in brown rice. Theanine is found almost only in the tea plant: a study of 37 commercial teas found an average of 5.13 to 6.56 mg per gram, depending on the type. Neither has a Thai Reference Daily Intake (Thai RDI).

In short:

• What they are: amino acids that are not used to build proteins
• GABA in food: germinated brown rice, tomatoes (more before they ripen), fermented foods
• Theanine in food: tea leaves (white, green, oolong and black tea); little in pu-erh
• Thai research: GABA in germinated Thai rice and in kung-som (fermented shrimp)
• Thai RDI: none for either

This article explains what the two substances are and how much of them foods contain. For the amino acids the body uses to build protein, see What are essential amino acids?

What are GABA and theanine?

The amino acids most people know are the ones that join together to make proteins. GABA and theanine are amino acids too, but they are found free, not built into proteins. Researchers at Prince of Songkla University describe GABA as a non-proteinogenic amino acid, and a 2023 review from Anhui Agricultural University in China describes theanine as a tea plant-specific non-proteinogenic amino acid.

Two amino acids at a glance

What the name GABA means

PubChem describes GABA as a gamma-amino acid: butanoic acid, a four-carbon acid, with an amino group on carbon 4. "Gamma" in the name refers to that position of the amino group.

What theanine is made of

PubChem names theanine N5-ethyl-L-glutamine: the amino acid glutamine with an ethyl group added to its side chain. PubChem notes that it has been isolated from green tea.

Which foods contain GABA?

GABA is found in many plants and in foods made by fermentation. The food that Thai research has studied most is germinated brown rice (ข้าวกล้องงอก), made by soaking brown rice until it starts to sprout.

White rice, brown rice and germinated brown rice

A 2023 study from Walailak University compared white rice, brown rice and germinated brown rice made from Yoom Noon, a southern Thai rice variety conserved under a royal initiative project in Nakhon Si Thammarat.

The same study found that germinated brown rice had the most protein and dietary fibre of the three, while white rice had the most carbohydrate.

Figures from other Thai studies

The figures use different units and methods, so they show a range rather than one number for all germinated brown rice.

Why germination raises GABA

A 2009 study from Kasetsart University found that as steeping time increased or the steeping water became more acidic, flour from both ordinary and glutinous germinated brown rice had more free GABA. A 2013 study from Chulalongkorn University developed a process of repeated soaking at 35 °C and incubation at 37 °C during germination, which gave the highest GABA. Long germination produced an unpleasant smell from microorganisms, which a 0.5% lactic acid soak controlled without changing GABA production or taste. How the rice is germinated therefore changes how much GABA it ends up with.

Tomatoes

A 2015 review from the University of Tsukuba in Japan describes the tomato as one of the major crops that build up relatively high levels of GABA in the fruit. The level changes a great deal as the fruit develops: it rises from flowering to the mature green stage, when GABA can make up to 50% of the free amino acids, and then falls rapidly as the fruit ripens.

Is there GABA in Thai fermented foods?

Some lactic acid bacteria, which are common in fruits and fermented foods, can make GABA naturally. Thai researchers have looked for them in local fermented foods.

Bacteria from Thai fermented foods

A 2020 study from Chiang Mai University obtained 36 isolates of GABA-producing lactic acid bacteria from Thai fermented foods. One isolate, taken from a Thai fermented sausage, produced 2.85 mg of GABA per millilitre in laboratory culture. This is a measure of what the bacteria can make in the lab, not of how much GABA is in the sausage.

Kung-som

Kung-som (กุ้งส้ม) is a Thai fermented shrimp. In a 2017 study from Prince of Songkla University, researchers added a lactic acid bacterium native to kung-som as a starter culture, together with 0.5% monosodium glutamate. The kung-som reached up to 10,500 mg of GABA per kg of fresh product, about four times the amount in kung-som made without the starter and in commercial kung-som. The starter also shortened fermentation from up to 19 days to under a week. These were experimental batches; the commercial kung-som in the study had less.

Which foods contain theanine?

Theanine is closely tied to tea. A 2023 review from Anhui Agricultural University in China describes it as a tea plant-specific amino acid and the most abundant free amino acid in tea leaves. It gives tea infusions part of their savoury, umami taste, and its content in the leaves is directly linked to the quality and price of green tea.

Where theanine is made in the tea plant

The same review explains that the tea plant makes theanine mainly in its roots and then moves it to the new shoots. The amount in the leaves depends on the cultivar, the season, nutrients and growing conditions.

Theanine in different types of tea

A 2016 study from the University of Szeged in Hungary measured theanine and caffeine in 37 commercial white, green, oolong, black and pu-erh teas.

The authors found that theanine varied widely within each type of tea, so the type of tea alone did not predict how much theanine a sample contained. Black teas were slightly lower, and pu-erh had practically none. The study was done in Hungary, and Thai teas were not tested.

How do GABA and theanine differ?

Both are amino acids that are not used to build proteins, and both are named after their structure. Beyond that, they come from different foods.

Is there a recommended daily amount?

GABA and theanine are not nutrients with a Thai Reference Daily Intake (Thai RDI), so there is no recommended daily amount for either in Thailand. The food figures in this article describe how much the foods contain, not how much anyone needs.

Amounts differ a lot between foods

The studies here show wide ranges: GABA in germinated brown rice depends on how it is germinated, GABA in tomatoes depends on ripeness, and theanine varies within each type of tea. A single figure for "GABA in rice" or "theanine in tea" is therefore only a rough guide.

Who should talk to a doctor or pharmacist?

If you are pregnant, breastfeeding, or taking prescription medication, check with a doctor or pharmacist before taking supplements.

Dietary supplements are not intended to prevent, treat or cure any disease.