Gut Health and Caffeine

Many people rely on a cup of coffee to kick-start their day. But that energizing jolt of caffeine can have notable effects on the digestive system, both positive and negative.

In this note we take a more in depth look at the science behind caffeine and the gut. We explore how caffeine stimulates our nervous system, how it can speed up digestion (sometimes a bit too much), its impact on sensitive guts (like those with IBS) and even how it ties into sleep and gut health.

Caffeine as a Stimulant: Impact on Brain and Gut

Caffeine is considered a drug because it stimulates the central nervous system, increasing alertness and countering fatigue. Part of this “fight or flight” boost comes from caffeine prompting the release of adrenaline (epinephrine) – the hormone that raises heart rate and energises the body. However, caffeine’s stimulatory effect isn’t limited to the brain. It also activates the nervous system in our gastrointestinal tract, causing intestinal muscles to contract more rapidly. In simple terms, caffeine can “fire up” the gut, which leads us to its effects on digestion and bowel movements.

Digestive Effects: Speeding Up Digestion and Bowel Movements

One reason many feel the need to visit the toilet after a morning coffee is that caffeine can act as a laxative. Multiple studies suggest that caffeine increases bowel activity. In general, caffeine speeds up peristalsis (the wave-like contractions that move food through the gut). This means food and waste travel faster through the intestines, which for some people can result in looser stools, diarrhea, or sudden urgency to go. Essentially, that morning latte might “get things moving” a bit quicker than usual, leading to cramping or an urgent trip to the loo in sensitive individuals.

Caffeine, IBS and Sensitive Guts

For people with irritable bowel syndrome (IBS) or otherwise sensitive digestive systems, caffeine’s effects can be especially pronounced. IBS involves a sensitive gut nervous system, and stimulants like caffeine can over-excite the gut, triggering cramps, urgency, and loose bowel movements. It’s no surprise that the NHS lists caffeine as a common trigger for IBS flare-ups. Health guidance in the UK recommends that those with IBS limit caffeine; for example, NHS advice is to have no more than 3 cups of tea or coffee per day to avoid worsening symptoms. Keeping caffeine in check (along with other triggers like alcohol or spicy food) can help calm an easily irritated gut.

Caffeine and Acid Reflux (Heartburn)

Caffeine can also aggravate acid reflux or heartburn in susceptible individuals. One way is by increasing stomach acid production - caffeine is known to stimulate the release of gastric acid in the stomach. More acid can mean a higher chance of it creeping up into the oesophagus. Additionally, caffeine belongs to a class of compounds (methylxanthines) that tend to relax the ring of muscle that normally tightens to prevent stomach contents from refluxing upward. Combined with more stomach acid this is a recipe for reflux: acidic contents can splash back up, leading to that burning sensation in the chest or sour taste in the throat. Coffee (and caffeine in general) is frequently cited as a food/drink that worsens heartburn. Notably, simply switching to decaffeinated coffee may not completely solve the problem - British dietary experts point out that both caffeinated and decaf coffee can exacerbate reflux symptoms. This suggests that components in coffee aside from caffeine (such as natural acids) can trigger acid reflux. In other words, caffeine plays a role in reflux, but coffee’s overall effect on heartburn involves more than just the caffeine.

Caffeine, Adenosine, and Sleep

Why does caffeine keep us awake? The answer lies with a brain chemical called adenosine. Adenosine naturally accumulates in our brain during the day – when it binds to its receptors, it produces feelings of drowsiness and signals that it’s time to rest. Think of adenosine as the body’s “sleep pressure”: the longer you stay awake, the more adenosine builds up, making you tired. Caffeine, however, has a similar molecular shape to adenosine, and it binds to those same receptors without activating them. By blocking the adenosine receptors, caffeine essentially prevents the brain from sensing how tired it really is. As a result, you feel alert and awake, even when your body has accrued a substantial sleep drive. This is great for shaking off grogginess, but it can lead to difficulties with sleep – caffeine in your system (especially if consumed later in the day) can delay the onset of sleep or reduce sleep quality since the brain’s normal adenosine signalling is being interfered with.

Poor Sleep and Gut Health

Caffeine’s influence on sleep is important for gut health because poor sleep itself can harm the gut. In fact, the relationship between sleep and gut is a two-way street. Research has shown that even a short period of sleep deprivation or an inconsistent sleep schedule can disrupt the balance of microbes in your digestive tract. After just two nights of insufficient sleep, studies observed:

• Reduced “good” gut bacteria: Levels of beneficial gut microbes drop when you don’t get enough sleep.
• Increased gut inflammation: Lack of sleep raises stress hormones and pro-inflammatory compounds, which can increase intestinal permeability (the so-called “leaky gut”).

This creates a vicious cycle: poor sleep disrupts your gut environment, and an imbalanced gut can in turn make it harder to get restful sleep. Many people with chronic gut issues (like IBS) report that their symptoms worsen when they haven’t slept well. There is emerging science to back this up. For example, a recent King’s College London study found that even a 90-minute variation in your usual sleep time (the kind of social jet-lag many experience on weekends) was associated with shifts in gut bacteria, including an increase in species linked to negative health effects. In short, sleep and gut health are deeply interconnected - protecting one can benefit the other. This also circles back to caffeine: if caffeine habitually disrupts your sleep, it may indirectly affect your gut health over time via these sleep-gut interactions.

Decaf, Half-Caf, and Low-Caffeine Alternatives

If you enjoy coffee or tea but want to avoid the tummy troubles or sleep problems associated with caffeine, there are strategies to manage your intake. One approach is switching to lower-caffeine or caffeine-free options. Decaf coffee or lower caffeine options let you still savour your morning cup while moderating your caffeine intake. This can reduce the stimulant impact on both your nervous system and gut. Many people find that cutting down the caffeine dose in this way helps with issues like jitteriness, urgency to use the toilet, or heartburn. It’s worth noting that even decaffeinated coffee can stimulate stomach acid due to compounds like chlorogenic acid in the beans. These acids can prompt the stomach to produce acid and speed up digestion, which is why some people sensitive to coffee still feel effects from decaf.

For individuals whose gut symptoms are primarily driven by caffeine itself (for example, caffeine-induced diarrhea or anxiety), a solid strategy is to reduce your intake of caffeine by replacing some coffees with decaf or lower caffeine options. For example, you might enjoy a decaf coffee in place of your second cup of regular coffee. By moderating caffeine in this way, you can still enjoy a coffee ritual while easing the impact on your gut and sleep.

Summary

In summary, caffeine affects not just our energy levels but also our digestive function - understanding these effects allows you to make informed choices, whether that’s cutting back on the espresso shots or switching to gentler alternatives, for the sake of your gut. At Calm Coffee Roastery, we specialise in coffees at lower caffeine levels – so you can enjoy a coffee ritual with the right level of caffeine for you. You can checkout our decaf and lower caffeine options here.

References

British Dietetic Association (BDA). (2022). Irritable Bowel Syndrome (IBS) and Diet. Retrieved from https://www.bda.uk.com/resource/irritable-bowel-syndrome-diet.html [Accessed 18 May 2025].

NHS. (2023). How to sleep well. Retrieved from https://www.nhs.uk/every-mind-matters/mental-wellbeing-tips/how-to-fall-asleep-faster-and-sleep-better [Accessed 18 May 2025].

Cox, S. R. et al. (2023). Social jetlag associated with adverse gut microbiome profiles in UK adults. King’s College London & ZOE Health Study. Published in the European Journal of Nutrition. Retrieved from https://www.kcl.ac.uk/news/irregular-sleep-patterns-harmful-gut-bacteria [Accessed 18 May 2025]