Two weeks without coffee are enough to change more than just your energy level

For many people, coffee is almost automatically part of the day. Upon waking up, after eating, during a work break, or before starting to study. We know that caffeine stimulates the nervous system and that suddenly stopping its intake can cause headaches, fatigue, or drowsiness. But what happens when we eliminate coffee from our routine seems to go far beyond just feeling low on energy.

A study published in April this year in Nature Communications precisely followed that process: it compared habitual coffee drinkers with people who did not drink it and then asked those accustomed to drinking it to completely eliminate it for two weeks. Later, they reintroduced it, this time divided between caffeinated and decaffeinated coffee.

The researchers did not limit themselves to observing whether they were more active or more tired. They analyzed their gut microbiota, metabolites, stress, sleep, memory, attention, anxiety, and behavior, among other parameters. The goal was to study an increasingly researched relationship: the one between what happens in our gut and what happens in our brain.

Two weeks without coffee to see what changes

The study initially included 62 healthy adults: 31 habitual coffee drinkers and 31 people who did not drink it. After the first evaluation, only the first group continued with the experiment.

For 14 days they stopped drinking coffee. Afterwards, 16 participants returned to drinking caffeinated coffee for three weeks and another 15 received decaffeinated coffee. This way, the researchers could observe not only what happened when withdrawing and reintroducing the beverage but also to what extent the changes really depended on caffeine.

And here appears one of the first keys of the work: coffee and caffeine are not synonyms.

A cup contains caffeine, but also polyphenols, melanoidins, and numerous compounds derived from the bean itself, roasting, and preparation. Some reach the intestine and come into contact with the bacteria that form our microbiota.

The microbiota also notices that we have stopped coffee

From the beginning, the researchers found differences between the gut microbiota of habitual coffee drinkers and those who did not drink it. It was not just about having more or fewer amounts of certain bacteria: substances produced or transformed in the intestine that participate in processes related to digestion and communication with the nervous system also varied.

For example, habitual consumers showed greater abundance of bacteria from the genera Cryptobacterium and Eggerthella and lower levels of several metabolites, including indole-3-propionic acid and GABA, a neurotransmitter involved in regulating nervous system activity. The study does not allow interpreting these differences as good or bad by themselves, but it does show that habitual coffee consumption leaves a biological footprint that goes beyond caffeine and the feeling of being more awake.

Moreover, part of those metabolic modifications changed when participants stopped coffee for two weeks and returned when reintroduced. Reintroduction altered the microbiota both with regular and decaffeinated coffee, which suggests that other components of the beverage also participate in that interaction. Among them are polyphenols and melanoidins, compounds that reach the intestine and have been linked in previous research to bacteria capable of producing short-chain fatty acids, substances important for intestinal health.

That is precisely what is interesting: a cup of coffee does not act solely on the brain through caffeine. It also comes into contact with an intestinal ecosystem capable of transforming some of its components and generating metabolites that later interact with other body systems.

That does not mean there is a single “coffee drinker’s microbiota” nor that drinking it is automatically beneficial for the gut. The composition of the microbiota also depends on diet, medications, environment, and numerous individual differences. But the experiment shows that a habit as everyday as drinking coffee every day leaves detectable changes and, at least in part, reversible when it disappears from the diet.

From the gut to the brain

The gut and brain maintain constant communication. This does not mean that an intestinal bacterium “directly controls” our mood or memory, but it does mean that the substances produced or transformed by bacteria are part of a network that also involves hormones, the immune system, and nerve connections.

That is why the researchers did not limit themselves to checking how the microbiota changed. They also measured stress, anxiety, sleep, impulsivity, attention, and memory to see if intestinal differences appeared simultaneously with changes in these functions.

And they found several striking coincidences. At the start of the study, habitual coffee drinkers showed greater impulsivity and emotional reactivity than those who did not drink it. When they stopped coffee for two weeks, both scores decreased. Later, upon reintroduction, both the group that took regular coffee and the one that received decaffeinated coffee recorded less perceived stress, depressive symptoms, and impulsivity than at the beginning of that phase.

Differences also appeared depending on the type of coffee. Those who resumed caffeine reduced some measures of anxiety and psychological distress and improved on an attention test. In contrast, the group that took decaffeinated coffee improved sleep quality and scored better on several memory tests, something especially interesting because it again points out that not all coffee effects depend on caffeine.

When analyzing all data together, the team also identified nine metabolites closely related both to certain intestinal bacteria and some of these cognitive measures. Among them were caffeine, theophylline, and several compounds derived from coffee polyphenols.

The interesting part is that intestinal changes and those related to sleep, memory, attention, or mood appeared in parallel, reinforcing the idea that coffee acts on several systems at once. The next step will be to clarify the weight of each mechanism and which of these relationships really respond to the microbiota, other coffee compounds, or the combination of both.

Quitting coffee did not produce exactly what was expected either

During the first days without coffee, some of the most well-known symptoms of caffeine withdrawal appeared, especially drowsiness and headache. However, both significantly decreased from the fourth day onward.

The most striking thing is that, as the two weeks of withdrawal progressed, participants did not feel progressively more tired. On the contrary: reported fatigue decreased and the feeling of energy increased. That is, the initial discomfort associated with quitting coffee did not persist throughout the entire abstinence period.

This result fits with an important idea to interpret the study: part of what we associate with coffee depends on the body's adaptation to habitual consumption. When it disappears from the routine, the first days can be uncomfortable, but that response does not necessarily remain the same over time.

So, what does this study really tell us?

The research was conducted with a small sample: 62 participants in the initial comparison and only 31 in the withdrawal and reintroduction phases. Also, its main objective was to study the microbiota, so results related to sleep, memory, anxiety, or attention should also be interpreted within that context.

Still, the experiment shows something especially interesting: coffee leaves detectable effects far beyond the feeling of being awake. When eliminated for a time and reintroduced, metabolites, certain intestinal bacteria, and several measures related to behavior and cognition changed.

And perhaps that is the most relevant part. We tend to reduce coffee to a simple equation: caffeine equals energy. But a cup contains many other compounds that also interact with the body and, in particular, with the intestinal ecosystem.

That is why analyzing what happens when we stop drinking coffee allows us to observe something that normally goes unnoticed: to what extent such an everyday routine relates to changes in the gut, metabolism, and some brain-linked functions.