L-Theanine for Weight Loss: Does It Really Work?

  • By Cristian Fry
  • 8 minute read
L-Theanine for Weight Loss: Does It Really Work?

Weight loss is always a big thing. While gaining muscle, increasing speed, improving reaction time, and other athletic goals come and go, losing weight usually ranks pretty high on the agenda for most people.

There is no shortage of products available to help you achieve your weight loss goals, be it all-natural fat burners, weight loss pills, or even just a solid diet and exercise program.

But where supplements are concerned, there’s one we hear a lot about for boosting cognitive function and maybe even enhancing sleep, but could it be helpful for weight loss?

While the mechanism behind how L-theanine exerts its effects is largely related to its direct influence on the central nervous system (CNS), it may have a more indirect effect on neural activity, making it a major player in the game for weight and fat loss.

So, we’re breaking down the ins and outs of L-theanine and if it should have a place in your fat-burning stack.

But first, let’s start with the basics—what is L-theanine?

What is L-theanine?

L-theanine is an amino acid naturally found in tea leaves that has been touted for its benefits in cognitive function and mental health because of its ability to block the binding of L-glutamic acid to glutamate receptors in the brain.

The potency of L-theanine in tea is the main reason why a steaming cup offers such relaxing effects. As such, it can influence psychological and physiological states during periods of stress and mental exertion 1.

Because L-theanine is a structural analog of the neurotransmitter glutamate, an excitatory brain chemical, it blocks the effects of glutamate and thus increases GABA, an inhibitory neurotransmitter that promotes calmness and relaxation. Animal studies suggest it may also increase brain serotonin and dopamine, both of which play a role in regulating mood 2.

But what we’re interested in with L-theanine in the sports nutrition world is its ability to potentially mitigate some of the nasty side effects of high-dose caffeine.

Studies show that L-theanine may inhibit CNS stimulation produced by caffeine, as well as reduce heart rate, lower subjective levels of perceived ‘stress,’ elevate visual attentional performance, and improve reaction time response 3, 4.

How? It has been shown to increase alpha brain wave activity without inducing drowsiness 5, and alpha brain waves are the brain activity exhibited during the relaxed, yet an inattentive state.

How It Works

Perhaps one of the best-known roles of L-theanine is in supporting cognitive function, which is why it’s a key component of all the best nootropic supplements. But that’s not all this guy does.

As mentioned before, the main mechanism behind how L-theanine works in the body is via the glutamate pathway. Because theanine is structurally similar to the excitatory neurotransmitter glutamate, it can weakly bind to glutamate receptors and acts antagonistically to elicit inhibitory activity on glutamate transporters 6.

As such, it blocks the reuptake of both glutamine and glutamate and inhibits their activity. It’s also been shown to increase dopamine and serotonin production in the brain, which plays a significant role in relaxation, reward, and mood through enhancing alpha brain wave activity.

In doing so, it can result in:

  • Better focus and attention
  • Reduced levels of stress and anxiety
  • Enhanced sleep quality
  • Better mood
  • Increased motivation
  • Better memory

What’s more, it can also inhibit the negative effects of caffeine on the brain. In short, caffeine works by antagonizing adenosine receptors in the brain to cause stimulation. L-theanine, however, reduces the physiological responses to stress by inhibiting excitatory responses in the brain.

When taken together, caffeine and L-theanine synergistically increase energy and alertness without causing side effects like high blood pressure, nervousness, and anxiety that typically come alongside high doses of caffeine 7.

Additionally, because caffeine is a vasoconstrictor, it temporarily decreases the diameter of blood vessels and causes an increase in blood pressure and a reduction in blood flow.

L-theanine can counteract these effects by reducing caffeine’s vasoconstrictive tendencies to increase blood flow and reduce the inclination for headaches and post-consumption fatigue.

But L-theanine is also known to counteract the effects that caffeine can have on sleep 8. Studies show that L-theanine targets caffeine’s propensity to reduce slow-wave sleep—the sleep needed for repair and restoration.

L-theanine may help increase both slow-wave sleep and REM sleep, which means an improvement in overall sleep quality and a reduced chance of depending on caffeine for next-day function.

Simply put, it supports only the finest-tuned stimulation for optimal performance without the side effect.

Benefits of L-theanine

In addition to what we just mentioned, studies have shown that L-theanine can exhibit a whack of other benefits in the body, including 6, 9, 10:

  1. Neuroprotection: L-theanine has been shown to protect against neural damage and improve cognitive function. It may help to inhibit certain neurological functions that result in reductions of antioxidants and oxidative damage. Nerve cell apoptosis (death) is also reduced with L-theanine supplementation.
  2. Reduce blood pressure: Studies show that L-theanine has anti-hypotensive properties with anti-stress activity by suppressing cortical neuronal excitement, reducing anxiety, and managing blood pressure during high-stress conditions via increasing the production of 5-HT (serotonin).
  3. Reduces fatigue: It may increase concentrations of dopamine and hepatic glycogen, along with reducing concentrations of 5-HT, which can contribute to physical exhaustion. Longer-term supplementation with L-theanine has been shown to further reduce levels of 5-HT, serum, urea, lactate, and increase both dopamine and hepatic glycogen levels, which serve as an important reserve during stress and intense activity.
  4. Boosts mood: L-theanine has been shown to have powerful anti-depressive and anti-anxiety effects that prevent stress-induced impairments to neuronal firing and memory via reducing heart rate and salivary IgA concentrations in response to stress. It may also attenuate an increase in sympathetic nerve activation or suppress the excitation of cortical neurons.
  5. Enhances brain function: As mentioned before, the ability of this amino acid to increase concentrations of brain neurotransmitters like dopamine, 5-HT, glycine, and GABA make it a powerful nootropic supplement for boosting cognitive function.
  6. Regulates sleep: Because of many of its inherent properties like modulating neurotransmitter activity and reducing physiological stress, studies show that a combination of L-theanine and GABA work synergistically to promote better sleep by decreasing sleep latency and increasing sleep duration. And we all know that sleep is a major factor in how well you perform in the gym and how well you recover. Without sufficient sleep, you can say goodbye to your gains.

Can L-Theanine Support Weight Loss?

While L-theanine offers all these amazing health benefits, the big question remains: Can L-theanine help with weight loss?

Its effects on physical and psychological state may offer a powerful indirect advantage for anyone looking to drop a few pounds, but L-theanine may also offer a more direct route to weight loss through a few main mechanisms.

1. Appetite Regulation

Have you ever felt the urge to binge on all the bad foods when you’re stressed? The phenomenon of ‘stress eating’ is real, and it can lead to some major side effects for your waistline.

While acute stress may curb your appetite due to the cascade of stress hormones that temporarily put eating on hold, chronic stress can have the opposite effect.

Studies suggest that long-term stress alters eating patterns and the salience and consumption of hyperpalatable foods, which could trigger neurobiological adaptations that promote compulsive eating behaviors 11.

Research suggests that it may be mediated by changes in the hypothalamic-pituitary-adrenal (HPA) axis, glucose metabolism, insulin sensitivity, along with appetite-related hormones and hypothalamic neuropeptides.

Altogether, these changes enhance reward sensitivity, food preference, and the need to consume hyper-palatable foods, resulting in weight and body fat mass changes.

However, a rodent study found that the anti-obesity effect of green tea, a popular weight loss supplement, is due to three major compounds—catechins, caffeine, and theanine 12.

Researchers found that the combination of caffeine and theanine was primarily responsible for the suppressive effect of green tea powder (GTP) on increases in body weight and fat mass.

2. Energy Metabolism

How your body handles energy has everything to do with body composition, and research suggests that L-theanine may play a role in regulating energy metabolism.

A 2021 rodent study on the effects of L-theanine in obese mice found that not only did consumption of theanine increase energy expenditure, but it also ameliorated obesity, improved glucose tolerance and insulin sensitivity, and reduced plasma triglyceride levels, total cholesterol, and free fatty acids in the mice consuming a high-fat diet 13.

Another study looked at the effect of green tea (GT) consumption containing L-theanine and caffeine or catechins on mice fed varying diets 14. They found that the high-fat diet with theanine and caffeine-rich green tea reduced the fat-promoting effects of a high-fat diet.

They concluded obese mice showed changes associated with abnormal lipid and energy metabolism, which were mitigated by consuming green tea containing L-theanine.

3. Fat Loss

Fat loss and weight management aren’t just a combination of a solid training program and a good diet. Other lifestyle factors like stress and sleep also play critical roles, and studies suggest that L-theanine’s sleep-promoting properties may support fat loss.

While there may not be a direct link between L-theanine consumption and fat loss, a large body of evidence suggests that sleep deprivation and poor sleep quality undermine dietary effort to reduce adiposity 15.

They repeatedly show that insufficient sleep may compromise the efficacy of typical diets for promoting weight loss and related metabolic risk reduction. And because L-theanine can improve sleep quality, it may be a key player in the game to achieving a healthy weight.

Final Thoughts

With all of that said, L-theanine hosts a long list of health benefits that you need to cash in on. But if you’re looking for weight loss, it also offers some good potential for regulating appetite and energy metabolism, both of which play a role in body composition.

Its known benefits for sleep can be a major bonus for anyone who struggles to maintain a healthy weight due to chronic sleep disruption.


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