Don’t Snooze On The Gut-Brain Connection When It Comes To Sleep

Sleep and gut health may at first glance appear like two separate domains– one in the realm of pillows and dreams, the other in the world of digestion, microbes and meals. Yet an emerging body of research shows these systems are intimately connected: the trillions of microbes in our gut (the gut microbiome) and the rhythms of our sleep–wake cycle (our circadian rhythm) engage in a dynamic, bi-directional conversation.

To help unpack this complex relationship, we turned to one of our AG1 Sleep Experts: Adriano Dos Santos, MSc, rNutr, IFMCP, MBOG, RSM—also known as The Circadian Nutritionist™—known for his work at the intersection of circadian biology, gut microbiome science, and personalized nutrition.

What are circadian rhythms, and why are they so important to health?

Dos Santos: “Circadian rhythms are 24-hour cycles that synchronise physiology (sleep–wake cycles, hormone release, metabolism, immune system) with the day–night cycle. Properly aligned rhythms (i.e., in synchrony with light, food and behaviour) allow physiological systems to operate smoothly; when misaligned (shift work, exposure to evening light, irregular eating times) they can contribute to the development of sleep disturbances, insulin resistance, inflammation and mood disorders.”

Circadian rhythms derive from an internal “clock” system within the body, anchored in the hypothalamic suprachiasmatic nucleus (SCN) in mammals and complemented by peripheral clocks in organs such as the liver, gut, kidney, and immune cells. These clocks generate predictable oscillations in gene expression, hormone release (e.g., melatonin, cortisol), metabolism, immune responses and other physiological processes.¹²³

Why is this so important? Misalignment of these rhythms (through shift-work, late-night eating, exposure to light at night or erratic sleep schedules) has been linked to a range of health issues: sleep disturbances, poorer glucose control, increased inflammation and mood disorders.⁴⁵⁶ In short: when internal rhythms match the external environment, physiology runs smoothly; when out of sync, the system is stressed.

How do the microbes in my gut affect my sleep and circadian rhythm?

Dos Santos: “Through multiple pathways: Gut metabolites (especially short-chain fatty acids, SCFAs) can affect clock-gene expression and neurotransmitters; immune signals influence neuroinflammation; and the vagus nerve carries microbial signals from the gut to the brain. These pathways may influence sleep architecture, REM/NREM cycles and clock gene timing.”

Let’s unpack that. Research increasingly shows the gut microbiome actively interacts with the body’s internal clock. Many of our gut microbes follow diurnal rhythms- meaning they operate on their own 24-hour cycles.⁶⁷ Short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate, are produced when gut microbes ferment dietary fiber and have been shown to influence clock gene expression through mechanisms such as histone deacetylase (HDAC) inhibition and G-protein-coupled receptor (GPCR) activation. In a systematic review, dos Santos’ team found that these gut-derived compounds may play a key role in regulating circadian processes.⁸

Are certain nutrients affecting my sleep more than I realize?

Actually, fiber often gets overlooked when it comes to sleep, but it plays an important role in connecting the gut microbiome and our body’s internal clock. High-fiber diets feed gut bacteria that ferment fiber into SCFAs, supporting gut lining integrity and lowering inflammation. Research links fiber and prebiotics to improved sleep quality, less nighttime wakefulness, and healthier microbiome activity. By strengthening the gut barrier and reducing endotoxins, fiber helps prevent disruptions in circadian rhythms and metabolic balance.⁹

Dos Santos: “Fiber nourishes SCFA-producing gut bacteria. SCFAs can support gut barrier function, reduce inflammation, and signal to the brain through the vagus nerve and circulation. These effects are consistent with stable sleep and cardiometabolic health, and regular fiber intake is a practical way to “tune” microbiome signals that influence circadian health.”

What is chrononutrition, and why does timing of meals matter?

Dos Santos: “Chrononutrition is the study of how the timing of food intake interacts with circadian biology. Eating is a timing signal for peripheral clocks (e.g., pancreas, liver, gut, kidney and even blood). We showed in our last publication at the Frontiers in Physiology that daytime, regular eating supports metabolic flexibility and glucose control; late-night or irregular meals can disrupt circadian clocks and impair sleep and insulin sensitivity.”

Meal timing is increasingly recognised as a critical circadian cue. When you eat is almost as important (in some cases) as what you eat. Eating during the biological night (i.e., when the internal clock expects you to be asleep) can cause peripheral clocks to fall out of sync with the central clock, leading to reduced insulin sensitivity, larger post-meal glucose spikes, and poorer sleep outcomes.² Eating the bulk of calories earlier in the day and maintaining consistent meal times helps support both metabolic health and sleep via the microbiome–circadian axis.

What probiotic strains or dietary patterns stand out as particularly helpful for circadian or metabolic balance?

Dos Santos: “We know that there is not a single ‘magic’ probiotic, but rather ‘microbiome networks that impact both circadian and metabolic homeostasis’. However, there is strong recent evidence that there are specific strains that are involved in the sleep, circadian and ultimately metabolic processes. I call them somnobiotic or chronobiotic bacteria, which are various microbes that produce metabolites linked to relaxation, neurotransmitter synthesis, and rhythmicity support.”

Key somnobiotics include:

• Lactobacillus rhamnosus GG, L. plantarum and L. helveticus R0052 modulates GABA
• Faecalibacterium prausnitzii, Roseburia, Eubacterium, and Lachnospiraceae UCG004
• Bifidobacterium longum 1714™ improves stress response and other Bifidobacterium spp.
• Akkermansia muciniphila and Clostridium sporogenes
• Streptococcus thermophilus and Lactococcus spp

As Dos Santos describes, some gut bacteria may actually help your body relax and sleep better - these are often called “somnobiotics.” Certain microbes (Faecalibacterium, Roseburia, Eubacterium) make a compound called butyrate, which helps keep your gut lining strong and reduces inflammation - both important for deep, restorative sleep. Others, like Bifidobacterium longum 1714™, have been shown in studies to lower stress hormones and improve how rested people feel after sleep. Strains such as Lactobacillus rhamnosus GG and L. plantarum help increase levels of GABA and tryptophan - natural compounds that calm the brain and support healthy sleep–wake cycles. Microbes like Akkermansia and Clostridium sporogenes support gut–brain communication, helping your internal clock stay in sync. And others, such as Streptococcus thermophilus and Lactococcus, may support brain-signaling balance and help fine-tune sleep-related rhythms. In short: these beneficial bacteria act like tiny conductors, helping your gut, brain, and internal clock “play in harmony” to support better sleep and overall balance.

What lifestyle factors help balance circadian rhythms and support gut health?

Dos Santos: “Light, timing and diet quality are three main factors. Morning light and reducing mainly blue-light exposure in the evening helps; regular sleep and mealtimes day-to-day are important; and a fibre-rich, less-processed diet that nourishes short chain fatty acid (SCFA)-generating microbes is a good goal. Together, these practices promote central and peripheral clock genes stability and minimise metabolic stress.”

Let’s consider each of these three pillars:

1. Light exposure: Morning bright light helps entrain the central clock (SCN) and sets the tone for the day. Conversely, high blue-light exposure in the evening (from screens or lamps) delays melatonin onset and shifts circadian phase, which then can disrupt both sleep and downstream metabolic rhythms.
2. Timing of behaviours (sleep, meals): Consistency matters. Regular bedtimes, wake times, and meal schedules help keep circadian rhythms aligned. Irregular routines—such as shift work or social jet lag—can lead to circadian misalignment, altered microbiome rhythms, and metabolic disruption.⁵
3. Diet quality: Diets rich in whole, fiber-dense plant foods and low in ultra-processed foods and added sugars support a healthy, diverse microbiome, including SCFA-producing microbes. These microbes promote gut barrier integrity, reduce inflammation, and help synchronize circadian and metabolic rhythms.

Think of your microbiome as a key player in your body’s circadian orchestra. When it’s “in tune” supported by regular meals, adequate fibre, and consistent daily routines it helps keep your internal clocks synchronized. When it’s “out of tune” due to irregular eating, low fiber intake, or disrupted sleep it can contribute to misaligned circadian rhythms and metabolic disturbances.

The takeaway

Over the past decade, research has revealed that the gut microbiome is not just a player in digestion and immune health - it’s an integral part of the body’s time-keeping system. The rhythms of our microbes, their metabolic signals, our feeding schedules, light exposure, and sleep patterns all converge to shape how we digest, rest, repair, and regulate metabolism.

As Adriano Dos Santos puts it, “every meal becomes a circadian cue.” When light, meals, sleep, and the microbiome are aligned, the body’s physiological orchestra performs in harmony - supporting restorative sleep, balanced metabolism, and overall well-being. When these rhythms fall out of sync, even subtly, microbial activity can falter, inflammation rises, metabolism destabilizes, and sleep suffers.

Ultimately, caring for your sleep, metabolism, gut health, and circadian rhythm means paying attention to diet, light exposure, and behavioral timing. Your gut microbiome is a central mediator in this intricate system, translating lifestyle cues into rhythms that keep your body (and mind) in sync.