Are There Any Foods Rich in Theanine?

If you tend to hit a mid-day slump, you may want to trade your coffee break for an afternoon tea where you can find L-theanine, an amino acid known for its soothing effects and potential to improve concentration. Finding foods rich in theanine is a tough task, though.

Drinking a glass of green tea may come with a number of benefits thanks to the theanine.

"Theanine is an amino acid that can help calm you down, reduce stress and anxiety, as well as improve attention, focus, memory and learning," says Karen Kjaerulff, RDN, a dietitian in Delray Beach, Florida.

The reason has to do with how L-theanine interacts with brain chemicals called neurotransmitters. The amino acid increases levels of GABA, serotonin and dopamine, which signal the brain to help regulate your mood and concentration, says Diana Orchant, RDN, a dietitian in New York City. It's chemically similar to glutamic acid, which helps transmit nerve impulses to the brain.

When it comes to using theanine supplements for anxiety for its calming properties, more studies and research are needed on the topic. Supplement forms of theanine are often taken alongside other products, so it's difficult to determine if the amino acid supplement itself can actually help anxiety, according to the Mayo Clinic.

Theanine may also improve sleep quality, although larger, well-designed trials are needed, says Uma Naidoo, MD, director of nutritional and lifestyle psychiatry at Massachusetts General Hospital in Boston and a Harvard Medical School faculty member.

​Read more:​ Can Certain Supplements Actually Help With Anxiety?

In a March 2018 review in ​Food Chemistry​, researchers recognized L-theanine as a compound with potential medical value, yet pointed out that its current use is limited.

Clinical studies, according to the review, have shown L-theanine has a positive effect in regulating central nervous system disorders, and it's a choice ingredient in medications because of its anti-stress and neuron-protecting roles, which may help slow cognitive decline in dementia, particularly Alzheimer's.

While some teas are rich in theanine, and it's available in supplement form, it's not abundant in food sources. Here are the most common food sources of L-theanine.

While green tea tends to contain the most theanine, there are other tea varieties that are also rich with the amino acid.

All tea comes from the same plant, ​Camellia sinensis​, says Jaime Gnau, RDN, a clinical instructor in the Department of Biomedical Sciences at Missouri State University in Springfield, but how the leaves are processed determines different types of tea. Typically, 2 to 3 grams of loose tea leaves are recommended to brew an 8-ounce cup of tea, she says.

Here's the average content of L-theanine in different types of tea, according to Gnau:

• Green tea: 6.56 mg/g
• White tea: 6.26 mg/g
• Oolong tea: 6.09 mg/g
• Black tea: 5.13 mg/g

"It's important to note that L-theanine content in tea can widely vary due to preparation time and tea processing," Gnau says.

A word of caution: Herbal teas are not made from traditional tea leaves and do not contain theanine, Kjaerulff says.

"L-theanine is an amino acid found primarily in tea, as well as some mushrooms, such as porcini, but in small amounts," Gnau says.

As a water-soluble amino acid, theanine is absorbed through the intestines, and peak plasma concentrations occur about 50 minutes after eating, Gnau says.

The most effective way to get theanine in your diet is by drinking green tea, Dr. Naidoo says. But remember: Green tea does contain caffeine. "Drinking a large amount of green tea can cause nausea, irritability and GI upset because of the caffeine content," Dr. Naidoo says.

If using oral supplements, be sure to look for labeling indicating third-party testing such as the United States Pharmacopeia (USP), Gnau says. "This ensures the safety of the product since supplements are not regulated [like medications] by the Food and Drug Administration," Gnau says. Always talk to your doctor before starting any new supplements.

​Read more:​ What Is the Best Green Tea?