Caffeine and L-theanine: the Good, the Bad and the Myths

We all know that when you say "I need coffee”, you actually mean “I need caffeine” - and it seems we just can't get enough of the stuff! On the flipside, coffee and caffeine are associated with some negative effects: insomnia, hypertension, dehydration, and so on. Since many people drink coffee, often even multiple times a day [1], we felt it was our civic duty as a nutritionally complete food company to investigate if any of these negative effects associated with coffee and caffeine are actually true. 

The Good, the Bad, and the Myths

Most of us can probably relate: if we had to choose between coffee or cereal, the first thing we’d consume in the morning would definitely be the drink – not just because we love the flavour, but because we need it. We can still feel the sleep in our eyes, our movements are sluggish, and we feel that between going back to bed, or drinking a cup of coffee, the latter is probably better as it won’t get us fired. 

But why do we feel like we need it?

When digested, caffeine partly goes to your brain, where it picks a fight with adenosine, the neurotransmitter responsible for making you feel drowsy [2]. 

As the day passes, adenosine gets produced because you’re doing physical work, or because you’re using your brain intensively. Adenosine then sort of floats around until it finds a receptor it can bind to, which causes your muscles to relax and makes you feel sleepy [3, 4]. But caffeine prevents this from happening. Caffeine has a similar chemical structure to adenosine, but it doesn’t bind to the adenosine receptors - it just blocks them [5]. Just imagine your dog, hopping onto your favourite chair and claiming it. It wasn’t made for him, but he still sits on it. Rude.



Ideally, you wake up without any adenosine molecules in your system. Getting a good night’s sleep should metabolise them [6], but if you don’t sleep (well) enough, some of those molecules will linger. And then you wake up feeling groggy. 

Caffeine can also be a cause for your morning grogginess: because caffeine blocks adenosine, the adenosine molecules heap up [7]. By the time the caffeine wears off and adenosine can bind to its receptors again, this surplus of adenosine needs to be metabolised during your sleep. But because there is so much of it (you just had to drink that after-dinner espresso, didn’t you?) you’ll likely wake up with left-over adenosine in your body, making you groggy.

Anyway, based on these properties, you could say that caffeine is helpful: it’s known for being good at keeping you awake and alert, and rightfully so. But it can also turn drinking coffee into a vicious circle: you’re battling grogginess with coffee which leads to grogginess which leads to drinking more coffee which leads to…. You get the picture. Still, caffeine gets associated with some other things too. Keep reading to find out where some of these claims come from, and whether they’re actually true or false.  

Caffeinated drinks dehydrate the body

Caffeine in itself is dehydrating: it has a mild diuretic effect [8, 9]. This means that it promotes the production of urine, meaning you lose more fluid. This diuretic effect is probably the reason why the myth that “coffee dehydrates you” is still around. To actually have a significant effect on your hydration status, you’d need to consume at least 500mg of caffeine a day – roughly 5 cups of coffee [10–12]! It is a fact that caffeine causes you to lose more water, but since you consume the caffeine as a beverage, you make up for it. 

In short: coffee and other caffeinated drinks will not dehydrate you, especially if you drink them in moderation. 

Coffee or caffeine causes constipation

The myth that caffeinated drinks cause dehydration could actually be the reason why it’s also believed that they cause constipation. Dehydration can cause constipation: if you lose too much water there’s not enough fluids left to properly process your stools. But coffee doesn’t cause dehydration! And if, besides coffee, you also drink some water throughout the day, you’ll more than make up for the slight diuretic effect of the coffee. This way, there’s no way you’ll get constipated from consuming some caffeinated drinks. 

In fact, coffee might even have a slight laxative effect – not on its own, but in combination with stomach acid. In a study performed in 1986 it was found that both caffeinated and decaffeinated coffee stimulate the production of gastrin [13]. Gastrin is a hormone that promotes digestion and speeds it up, causing you to have to have a bowel movement [14]. In another study it was found that having a cup of coffee in the morning makes this process happen even faster: roughly twenty minutes after the subjects drank their coffee, they needed to use the bathroom already [15]. This doesn’t affect everyone, and the effects of caffeine differ per person. What we can conclude is that coffee does have an effect on your bowel movements, but it will most likely promote them rather than constipate you. 

Caffeine causes insomnia

Remember adenosine? This claim probably derived from exactly what caffeine does: it keeps you awake by blocking adenosine from doing its job. But whether that leads to a diagnosis of insomnia remains the question. Caffeine definitely can cause sleeping problems, especially when you consume it too late in the day, as it’ll increase the time it’ll take for you to fall asleep. On average, the time it takes for caffeine to wear off is around 6 hours, so drinking coffee a few hours before bedtime may mean having to count 5 million sheep before finally falling asleep [16]. According to some studies, caffeine can also decrease your sleep quality if you consume too much (more than 400mg a day) [17–19], but according to another study, the consumption of caffeinated beverages does not have a significant relationship with sleep quality [20]. 



When caffeine is consumed in low or moderate amounts during morning hours, people who normally do not have sleeping problems don’t experience any sleeping problems, and even people who do experience them usually do not feel like caffeine worsens these problems [21]. Of course, this is obviously only the case if you generally don’t possess a gene that could make you more susceptible to any of the effects caffeine might have on a person.

So, don’t fret. If you keep an eye on your own caffeine consumption and keep it low, you should be able to get enough rest during the night! If you want to accurately keep track of how much caffeine you’re consuming, you should try out our Plenny Shake Coffee! Each shake contains 25mg caffeine per 100ml, so roughly 100mg per 400 ml shake! 

Caffeine causes hypertension

Another commonly believed fact is that caffeine can cause hypertension. Let’s break down what this exactly means. 

When you have hypertension, it means that your blood pressure is constantly elevated for a long period of time, compared to your “normal” reading. Every person has different blood pressure, and what’s high for someone else might be normal for you. However, when your blood pressure is even higher on average during the majority of the day, you may get diagnosed with hypertension, often also called high blood pressure [22]. 

So, why is it believed that caffeine causes hypertension? Studies have shown that a cup of coffee with 140 mg of caffeine does raise blood pressure, but only for roughly 2 to 3 hours after consuming it [23]. It’s unsure why it goes up, it’s only been observed that it does go up. Because it only goes up for roughly 2 to 3 hours, you can argue that it raises your blood pressure, but it doesn’t necessarily mean that you have high blood pressure [24]. On top of that, it’s also concluded that the blood pressure elevations that happen after consuming caffeine are bigger in people who do not regularly consume caffeine [25]. From these studies can be concluded that caffeine does not give you hypertension, only temporarily elevated blood pressure.

However, if you do have hypertension, it’s advised that you keep track of how much caffeine you consume. You can definitely have a cup of coffee daily, as it seems unlikely that it has a significant effect on your BP, but if you start increasing your dose of caffeine, or suddenly start drinking caffeine when you usually never do so, it might increase your blood pressure [26]. 

You know yourself the best, so use this information to see what applies to you. If you’ve always been drinking your morning coffee and have hypertension, don’t worry, you’ll be fine. And if you don’t have hypertension and still drink it every day – you don’t have to worry either. Caffeine won’t cause it, but if hypertension does run in the family, you might want to get your BP checked regularly as genetics do play a role [27].

Caffeine helps you lose weight

Is coffee actually the magic drink that helps you lose weight? Several studies have pointed to different answers: some came to the conclusion that it plays a role, while others say it can’t be determined whether coffee plays such a big role, or whether the weight loss was a result of drinking coffee and having a healthy lifestyle with healthy eating habits. Let’s take a look at some of the findings.

First of all, keep in mind that the whole “coffee can help you lose weight” claim is about black coffee. A cup of coffee contains less than 5 calories per cup if you drink it black, but can actually cause you to gain weight if you add a lot of sugar, milk or cream, as it increases your calorie intake[28]. Pretty logical, right? 

With that in mind it might make sense as to why coffee could help you lose weight. As a cup is low in calories, it’s way better than drinking, say, a glass of Cola. Weight loss occurs when you burn more calories than you take in, so if you consume fewer calories by substituting a high calorie drink with a lower calorie drink, such as coffee, you might already be setting a step into the direction of weight loss (assuming you’re taking other steps as well). 

It’s also been found that the caffeine that’s in coffee boosts metabolism [29, 30]. A faster metabolism means you will burn more calories while “at rest”, meaning that you burn more calories while doing… Almost nothing! Yay! However, this doesn’t apply to everyone. As we said before, everything affects everyone differently: don’t get your hopes up too high – coffee might not even be the miracle weight loss drink you think it is!

Another effect caffeine has is that it might decrease your hunger feeling. A study from 2014 found that daily coffee-drinking caused their participants’ hunger feeling to decrease, as the ghrelin levels in their blood decreased [31]. Ghrelin is the hormone that causes you to “feel” hungry: it’s also dubbed the hunger hormone for this reason [32]. On top of that, drinking coffee can also increase the satiety hormone called peptide YY, which is the hormone responsible for making you feel satiated [33, 34]. This obviously means you’ll eat less.

On the other hand, other studies have concluded the opposite: some studies concluded that the intake of caffeine can promote weight loss, but the impact of the effect seems small, and whether it’s clinically relevant is also questionable [35]. Other studies found that caffeine might even hinder weight loss and instead cause you to gain weight. 

The reason for this is that caffeine can lead to reduced sleep, which we’ve mentioned above. Getting enough sleep is important in general, and if you want to find out why, check out our article on why sleep is important. In this case, getting enough sleep is also important, as reduced sleep can lead to a decrease of leptin [36], the hormone responsible for decreasing appetite, and an increase of ghrelin, the hunger hormone we’ve talked about before, which can lead to an increased appetite for high-calorie foods ) [37]. This craving, if repeatedly listened to, can lead to weight gain. Reduced sleep also means you have more time during the day, which means more time to eat. If you’re not good at controlling cravings in general, you might indulge more often, which is also a cause for weight gain. In short, drinking too much coffee or drinking it too late might be counterproductive if your goal is to lose weight. 

It’s safe to conclude that if weight loss is your goal, the solution is to be mindful of how much caffeine you consume and at what time. If you’re looking for some tips on how to lose weight, check out our guide to weight loss.

Then… It’s not bad?

Coffee, or caffeine in itself definitely isn’t bad for you – if you drink coffee or consume caffeine in moderation, you should hardly experience any problems, granted you’re healthy and not allergic to any ingredients. The most important thing to keep in mind when consuming caffeine is what time it is when you consume it, and when you’d like to go to bed. Just drink it in moderation, and don’t drink it too late, and caffeine can give you that boost that you might need in the morning. If you find that caffeine on its own can’t keep you focused, you could maybe even try a combination of caffeine and L-theanine.


L-theanine! What, you’ve never heard of it!? Just kidding, we don’t judge. We’ll explain it here anyway.

L-theanine is an amino acid that is mainly found in green tea. It’s what gives green tea its unique flavour [38] and it’s believed to improve mental function, as it has a similar chemical structure as glutamate [39]. Glutamate helps transmit nerve impulses in your brain (making it a neurotransmitter) and occurs naturally in your body. L-theanine behaves similar to glutamates as it binds to the same glutamate receptors, but the effect is different. Whereas glutamate has an excitatory effect (causing a neuron to fire an action potential), L-theanine has an inhibitory effect (preventing an action potential). Blocking the effects of glutamate stimulates the production of the neurotransmitter GABA, which has a stress-regulating quality and helps relieve anxiety [40]. In short, consuming L-theanine causes you to relax without making you drowsy, as it lowers your blood pressure as you’re less stressed.



L-theanine also has been found to cause better focus. During a study done in 2012, they observed people who ingested L-theanine or a placebo and found that the group who didn’t get the placebo made fewer errors in a sustained attention task and had improved focus [42]. In other studies, it’s been found that L-theanine combined with caffeine produced even better results when it came to focus [43]. It was found that people who had a dose of both caffeine and L-theanine were better at attentional switching and were faster and more accurate when doing so [44]. 

So, caffeine in itself is beneficial already when the goal is to stay awake and feel less tired, and apparently, L-theanine on top of caffeine seems to increase your focus as well.

So, you’re saying… Chug all the coffee!?

No, no, no! Didn’t you pay attention? Don’t drink too much! Caffeine definitely has its good qualities, but you should definitely not drink all of the coffee you can find, as it’ll be detrimental to your health. As long as you don’t overdo it and keep your caffeine intake below 400mg a day, you should be fine. So, are we suggesting you should mix up your coffee with green tea then? You’re free to experiment of course, but to make things a little easier we developed the Plenny Bar Mocha, which has 15mg of caffeine per 400 kcal bar! Great for on the go, can serve as both your morning coffee and breakfast, and will help you stay focused to boost your productivity. Plus: filled with 26 vitamins and minerals, rich in fibres, 20g of protein, and much more good stuff!

So what is it going to be? A plain old regular coffee, or a deliciously nutritious  Plenny meal? 



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