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Foods Rich in Theanine

author image Janet Renee, MS, RD
Janet Renee is a clinical dietitian with a special interest in weight management, sports dietetics, medical nutrition therapy and diet trends. She earned her Master of Science in nutrition from the University of Chicago and has contributed to health and wellness magazines, including Prevention, Self, Shape and Cooking Light.
Foods Rich in Theanine
Tea is rich in antioxidants. Photo Credit KOICHI SAITO/amanaimagesRF/amana images/Getty Images

Available as a dietary supplement, theanine is used to boost focus and concentration as well as to promote relaxation. The amino acid is found in rich amounts exclusively in tea. Research suggests it may enhance brain function and help your body deal with stress. While consuming theanine from tea is relatively safe, consult your health care provider if you're considering taking theanine supplements.

Theanine in the Diet

Some manufacturers add theanine to commercial beverages. Tea is the only naturally occurring source of the amino acid in your diet, however. Theanine comprises 1 percent to 2.5 percent of the dry weight of tea leaves. Because it's highly water-soluble, when tea is prepared, nearly all of the theanine from the leaves dissolves in the water. The theanine content of tea leaves varies, but green tea contains a richer amount than other teas, according to Billie J. Sahley, author of the book "L-Theanine: The Relaxation Amino Acid."

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Enhances Brain Activity

The Asia Pacific Journal of Nutrition published a study in 2008 confirming that theanine in amounts found in tea enhances brain activity. Researchers examined the brain activity of healthy adults after they consumed theanine. The researchers found that theanine significantly increased alpha brainwave activity. Alpha waves promote relaxation without causing drowsiness, which allows you to remain focused and alert, yet calm. A second study successfully replicated these results, the authors noted. The results show that theanine helps improve concentration and alertness, according to the study.

Combats Stress

Theanine appears to help combat stress, according to a study in the journal Pharmacology, Biochemistry and Behavior published in October 2013. Scientists evaluated the effect of theanine on graduate students during pharmacy practice. They found that theanine significantly lowered stress markers in the students under the stressful situation of pharmacy practice compared to a placebo group. The authors concluded that theanine may be useful as an anti-stress agent.

Precautions for Tea and Supplements

Herbal teas are not made from traditional tea leaves and thus do not contain theanine. Regular varieties of tea like green, black and oolong that contain theanine also supply caffeine. For this reason, it's not a good idea to drink large amounts of tea in order to get more theanine, as you may experience side effects from excess caffeine. Decaffeinated teas contain theanine concentrations comparable to caffeinated teas, according to Sahley.

Taking theanine supplements may decrease blood pressure, according to the Cleveland Clinic. If you have problems with blood pressure, talk to your health care provider before taking theanine.

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