Caffeine and Metabolism

A cup of black coffee on a table with food in the background.

For most of us, coffee or tea in the morning is a must. So much so that the smell of coffee in the morning becomes unanimous with waking up and getting going for the day – and for an obvious reason: caffeine. Coffee and tea are popular morning staples for many adults because they provide a small kick to wake you up.  

Caffeine is the most popular substance consumed all over the world. Approximately 80% of the world’s population consumes caffeinated products every day, and 90% of adults in North America consume caffeine on a daily basis. Caffeine is found in various foods and drinks such as coffee, tea, cola, energy drinks, chocolate, cacao, kola nuts, and supplements. The most popular ways of consuming caffeine are of course, drinking tea and coffee, with coffee being the most concentrated source of caffeine. 

For centuries, products containing caffeine have been consumed all over the world across cultures for the purpose of increasing alertness and energy levels. Because caffeine is a stimulant, it’s common to think that because coffee gives you that energy boost, it must also make your metabolism work faster. But, is that or is it a myth? Does caffeine actually have an impact on the fuel you burn, or how efficiently your body uses it? Let’s see what science says about it:

Caffeine has a significant impact on metabolism 

It’s a fact that caffeine is the most widely used brain stimulant in the world. The substance is rapidly absorbed in the gut and raises its concentration in blood after only 15 minutes, this means you can experience some of its effects just a few minutes after you take the first sip of coffee. In addition to the effects you feel in mood and energy, caffeine has an impact on numerous functions in the body:

Caffeine impacts different body tissues in a variety of ways

Caffeine affects the central nervous system, the release of hormones, renal function, cardiovascular (heart and blood vessels) function, and many other bodily functions. The half life of this substance, which is the amount of time it takes to your body to eliminate its presence by 50%, ranges from 5 to 9.5 hours, which means caffeine’s effects can last for many hours. There are many factors related to this wide variation in caffeine’s half life, such as genetics, body weight, body composition (fat mass and muscle mass percentage), smoking and of course, what the dosage is (how much caffeine you consume). Tolerance to caffeine is another factor , among others factors. When it  comes to metabolism, here’s how caffeine breaks things down (literally!):

1. Caffeine has a fat burning effect:

The main mechanism related to this is by blocking the receptors of a neurotransmitter called adenosine. This allows an increase in the activity of enzymes in charge of breaking down the adipose tissue (fat) for producing energy, a process known as lipolysis .

2. Caffeine can have a positive impact on weight management: 

Caffeine stimulates the nervous system which helps to create satiation signals decreasing hunger levels at the same time. Studies have shown that caffeine can slightly increase your energy expenditure, especially in active people, which can help you to burn more calories. 

3. Caffeine improves performance: 

This substance is classified with the highest level of evidence (level A) according to the Australian Institute of Sports which means, its benefits in sports have been widely reported by multiple studies. Research shows that because caffeine interacts with chemical substances called neurotransmitters, it improves endurance exercise performance by increasing fat mobilization from adipose tissue for producing energy, allowing for “spare” muscle glycogen. Caffeine has also proved to be an effective supplement for short-duration high intensity exercises (1-5 min), such as in HIIT, as well in ultra endurance events (more than 4 hours) and also in team sports.

In addition, the improvements in performance are not related only to enhaced fat burn, but also to other benefits associated with caffeine such as: 

  • reduction of fatigue
  • Increase in energy levels 
  • Improved concentration
  • Improved reaction speed 
  • Improved motor function 

4. Other effects of caffeine

Under certain individuals and under certain conditions, caffeine consumption has also been linked adverse effects where the main factors involved are related to the amount of caffeine consumed, the individual’s genetic susceptibility metabolize this substance and also, specific conditions related to the person such as the biological state (pregnancy, breastfeeding), specific medications, and sleep disorders where caffeine is not recommended at all.

The common factor among all these is that caffeine stimulates the nervous system, and because of that it has also been shown to increase the release of adrenaline and cortisol hormones. While this effect is usually not significant in most populations, it can generate a shift towards burning carbs due to the body’s fight or flight response generated by these hormones. Moreover, these hormones are also related to other side effects such as increased heart rate, appetite suppression, irritability, anxiety and sleep disruption. 

The body’s response to caffeine

The response to caffeine is not the same for everyone – and there are multiple reasons  for this, recent findings have confirmed that a major factor is related to the genes. 

The genes control the enzyme activity, which have the tough task of keeping all your metabolism working with an outstanding synchronization. New evidence suggests that individuals can have a greater capacity for metabolizing caffeine, meaning they can tolerate higher doses of caffeine and experience less adverse effects, these are known as fast metabolizers.  

Conversely individuals having other genetic variations can be slow metabolizers, meaning it takes for them more time to process caffeine, and are more likely to experience adverse effects such as the ones described above. 

Lumen and Caffeine

As a device that measures your metabolism in real-time, Lumen’s is researching the impact of caffeine on the Lumen measurement results. If you are a Lumen user and would like to participate in the study, click here to sign up. Please note that we need participants to follow a 5 day measurement protocol and drink straight black coffee. 

The take home message: 

  • Caffeine can have a significant impact on the fuel you burn (fats vs carbs).
  • More is not better, while caffeine has proven benefits in the metabolism, these are dose-dependant, meaning, the amount you consume matters.  
  • We all respond differently to caffeine, there are multiple reasons such as gender, the genetics, the body weight, the habituation, among many others. 
  • Know your body, the best way to realize the impact of caffeine in your metabolism is to test it by yourself, as different people have different sensitivities and react differently to caffeine. 


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  • Hodgson AB, Randell RK, Jeukendrup AE. The metabolic and performance effects of caffeine compared to coffee during endurance exercise. PLoS One. 2013;8(4):e59561. 
  • Harpaz E, Tamir S, Weinstein A, Weinstein Y. The effect of caffeine on energy balance. J Basic Clin Physiol Pharmacol. 2017 Jan 1;28(1):1-10. 
  • Tabrizi R, Saneei P, Lankarani KB, et al. The effects of caffeine intake on weight loss: a systematic review and dos-response meta-analysis of randomized controlled trials. Critical Reviews in Food Science and Nutrition. 2019 ;59(16):2688-2696
  • Pickering C, Kiely J. Are the Current Guidelines on Caffeine Use in Sport Optimal for Everyone? Inter-individual Variation in Caffeine Ergogenicity, and a Move Towards Personalised Sports Nutrition. Sports Med. 2018 Jan;48(1):7-16.
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