Does L-Theanine Help with Weight Loss? | Scientific Studies

You are more likely to run into the amino acid l-theanine as a nootropic ingredient than in a fat loss supplement. Its benefits to cognitive function have been covered extensively (including by me here). But how about weight management? Is l-theanine an asset to your weight loss plan? I have pored through the science to establish if the claim of weight loss efficacy is factual.

Key Points

  • L-theanine is best known as a nootropic supplement but may help with weight loss.
  • The overwhelming majority of research on l-theanine’s weight loss capabilities has involved animal studies.
  • L-theanine has been shown to reduce body weight, suppress fat accumulation, increase energy expenditure, improve insulin sensitivity, increase glucose tolerance, reduce bad cholesterol, increase good cholesterol, regulate protein metabolism and improve sleep quality.

What is L-Theanine

L-theanine is a non-protein water-soluble amino acid naturally occurring in the tea plant (Camellia sinensis) as well as some mushrooms. It contributes to tea’s favorable taste. L-theanine is best known for its ability to lower anxiety and stress but has sometimes been linked to weight loss. Let’s get to the studies.

L-Theanine and Weight Loss Studies

L-theanine isn’t an amino acid that routinely comes up in weight loss supplement conversation. So unsurprisingly, the bulk of studies on its weight loss efficacy have been done on animals. Human studies are few and far between.

Body Weight and Body Fat

In 2004, scientists set out to assess the anti-obesity effect of theanine, catechins, caffeine and green tea. For this study, they fed female mice diets containing these compounds single and in combination over a 16-week period. Mice on diets containing theanine saw a reduction in body weight. 

The results suggested theanine was one of the key compounds behind green tea’s ability to suppress fat accumulation and weight increase.

Thermogenesis and Blood Sugar Regulation

In 2021, researchers associated with the American Diabetes Association subjected mice to l-theanine treatment. They found that l-theanine enhanced thermogenesis and increased energy expenditure. In the sub-group placed on a high fat diet (HFD), l-theanine appeared to prevent obesity, improve insulin sensitivity and increase glucose tolerance. 

Increased thermogenesis and improved blood sugar regulation are crucial for weight loss and weight loss maintenance.


In a 2022 study, mice were fed with normal diet, HFD and HFD + l-theanine over a 16-week period. The data showed the mice on l-theanine showed a significant reduction in body weight and LDL cholesterol (bad cholesterol). 

Another study a few years earlier involved 400 day-old broiler chicks that were randomly placed on a placebo or varying quantities of l-theanine supplementation. Chicken on 200 mg/kg l-theanine exhibited a decrease in total cholesterol but an increase in HDL cholesterol (good cholesterol). However, they had faster weight gain.

Reducing levels of bad cholesterol is one of the main reasons people lose weight. This is definitely a plus on l-theanine’s weight loss scoreboard. The weight gain in the broiler chicks study is however concerning and would be counterproductive.

Sleep Quality

Natural weight loss stands on three core pillars –

  • exercise, 
  • healthy diet and
  • adequate sleep. 

You could however infer l-theanine’s contribution by looking at how it affects one of the main factors that impact weight gain – insomnia. And finally, here comes a human study.

2018 survey by the University of Arizona for example found a link between poor sleep on the one hand and junk food cravings and nighttime snacks on the other. Of 3,105 respondents, two in three reported a lack of sleep caused them to crave for junk food.

What does this have to do with l-theanine you ask? L-theanine has been shown to improve sleep quality. A 2011 review established that administration of l-theanine before bed can improve sleep quality and without causing daytime drowsiness.

Dosage Recommendation

L-theanine is widely used in nootropics and some weight loss supplements. The numerous studies on its cognitive benefits makes it relatively easy to figure out what is the ideal amount for that end goal. Weight loss is a whole different ball game. The amounts that work for cognitive enhancement may not do so for weight loss. Major fat burners that contain l-theanine have it in the 100 to 250 mg daily serving range.

Wrapping Up

I’d love to tell you unequivocally that l-theanine is great for weight loss. But I can’t do that. While animal studies make a strong case for it. The scarcity of human studies around the subject mean l-theanine is not really something you should turn to as a primary supplement for a weight loss plan. However, its proven benefits in improving sleep quality (a risk factor in weight gain) implies it can complement the actions of compounds and elements that can more directly drive weight loss.

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About the Author

Sam is a passionate health and fitness enthusiast who has been interested in supplements, fitness, and wellness for over 10 years. He is the founder of Great Green Wall - the health and wellness brand and has completed multiple fitness certificates, including personal training and nutrition certifications. Sam has been working as a personal trainer for the past three years and is dedicated to helping his clients achieve their fitness goals and lead healthier lifestyles. He believes that a healthy lifestyle is crucial to a happy and fulfilling life and is committed to sharing his knowledge and passion with others.

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