If you’ve ever noticed that your digestion feels a bit “off” in the evenings — or that reflux seems to flare up just as you’re trying to sleep — you’re not alone. Our digestive system runs on its own internal clock, quietly guided by circadian rhythms that influence everything from hunger and enzyme activity to stomach acid production.
When we eat at times that don’t quite fit that rhythm, or when stress and disrupted sleep throw it off course, digestion can start to struggle.
And for many people, this shows up as night-time reflux, bloating, or a sense that food just sits too long.
Let’s look at what this internal timing looks like — and why understanding it can help bring digestion back into balance.
A Natural Rise and Fall
We often think of stomach acid as something that only appears when we eat, but it’s actually produced around the clock — just in varying amounts. Research shows that basal acid secretion rises naturally during the late evening and early night, peaking somewhere between 10 pm and 2 am (Moore, 1991; Vaughn et al., 2014). That may seem odd — after all, our ancestors weren’t sitting down to big dinners at that time of night! But this pattern makes sense once we look at what the body’s trying to achieve.
Why We Produce More Acid at Night
From an evolutionary point of view, higher acid levels overnight served a few important purposes:
- Keeping the gut clean: The stomach’s acid helps reduce harmful bacteria — a sort of natural night-time disinfectant.
- Preparing for the day ahead: A stomach that’s “primed” with acid first thing in the morning can digest food more efficiently.
- Supporting a balanced microbiome: Consistent acid levels overnight discourage bacterial overgrowth in the upper gut.
So, the body’s intention was never about digesting a midnight feast — it was about protection and preparation.
When Modern Life Gets in the Way
Fast forward to today and our lifestyles look very different. Late dinners, snacking in front of the TV, disrupted sleep, and the widespread use of acid-suppressing medications all interfere with that natural rhythm.
This combination can set up a bit of a vicious cycle:
- Reflux and indigestion: Eating when acid levels are naturally higher can push contents back up into the oesophagus.
- Weaker digestion: If sleep or medication suppresses acid at the wrong time, we may not break down food efficiently.
- Microbiome shifts: Less acid means more opportunity for bacteria to move into areas they shouldn’t.
- Nutrient shortfalls and fatigue: Over time, reduced absorption and inflammation can leave us feeling flat (Bishehsari et al., 2025).
Essentially, the stomach’s finely tuned timing clashes with our modern schedules — and the result can be ongoing digestive discomfort.
Simple Ways to Realign Your Rhythm
The good news is that you don’t need to overhaul your life to work with your gastric rhythm. A few small shifts can make a real difference:
- Keep evening meals light and earlier where possible. Try not to eat too close to bedtime — and if reflux is a problem, smaller portions and gentler foods are your friends.
- Support your digestion naturally. If you’re on reflux medication or notice that your digestion feels sluggish, gentle support for the stomach can help — such as mindful eating, thorough chewing, or including bitter foods before meals. If you’re considering supplements, it’s best to speak with a qualified nutrition professional for individual advice.
- Focus on good sleep habits. Regular sleep times, a dark room, and calming evening routines all support the nervous system and healthy acid balance.
- Discuss medication timing with your clinician. Adjusting when you take your PPI (for instance, before breakfast rather than in the evening) can sometimes reduce night-time issues.
These small adjustments help you work with your stomach’s natural timing — not against it.
In Summary
Our stomach acid follows a rhythm that evolved to keep us healthy — cleaning, protecting, and preparing the gut overnight. But modern life often runs on a completely different schedule, leading to reflux, bloating, and disrupted sleep. Understanding and respecting that rhythm is a simple but powerful way to restore digestive harmony.
References
- Moore JG. Circadian dynamics of gastric acid secretion and pharmacodynamics of H₂ receptor blockade. Ann NY Acad Sci. 1991; 618:150–158.
- Vaughn BV, Rotolo S, Roth HL. Circadian rhythm and sleep influences on digestive physiology and disorders. Chronobiol Int. 2014; 31(9):1011–1022.
- Bishehsari F et al. Circadian rhythms in gastroenterology: the biological clock’s role in gastrointestinal health. Gastroenterology. 2025; 168(1):1–13.
Disclaimer
This article is for general educational purposes only and is not intended to diagnose, treat, or replace medical advice.
If you are experiencing digestive symptoms or take prescription medication, please consult your GP or a qualified healthcare professional before making any changes to your diet or supplement routine.