How to improve gut health for sleep, stress, and performance

Originally published on August 7, 2024

Gut health affects digestion, sleep, stress tolerance, and even heart rate variability. In Episode 283 of the WHOOP Podcast, Global Head of Human Performance, Principal Scientist at WHOOP Kristen Holmes speaks with Dr. Megan Rossi, founder of The Gut Health Doctor, about what a healthy gut actually looks like, why gut testing still has limits, and which habits have the strongest evidence behind them.

Rossi is a registered dietitian, nutritionist, and gut health researcher with an award-winning PhD recognized with a Dean’s Award for Outstanding Research. Her framework is practical: build a resilient microbiome with food diversity, protect it with sleep and stress management, and treat supplements as targeted tools rather than shortcuts.

To listen to Episode 283 of the WHOOP Podcast in full, head to the WHOOP Podcast on YouTube.

What is a healthy gut, and can you improve it?

Yes. Rossi’s answer to Holmes was clear: people have agency over gut health, and a healthy gut shows up as better day-to-day function, not as a perfect lab number.

Rossi defines a healthy gut as one that supports regular digestion, helps you avoid getting sick all the time, and contributes to better sleep, steadier stress handling, and stronger mental health. That definition fits what researchers now understand about the gut microbiome: trillions of microbes interact with the immune system, the enteric nervous system, and hormone signaling. Gut health is not confined to bowel symptoms alone.

That wider frame matters for women’s health, too. Rossi noted that hormone changes can alter gut function, which helps explain why looser stools around menstruation are common. She also highlighted the estrobolome, a group of gut microbes involved in estrogen metabolism. Research in this area is still catching up, but the direction is clear enough that Rossi sees gut support as relevant to conditions such as PCOS and menopause. For more on nutrition, women’s health, and the difference between prebiotics and probiotics, see Episode 198 with Dr. Hazel Wallace.

Rossi tied all of that back to a simple point: the gut is deeply connected to whole-body function, so the quality of your digestion, sleep, mood, and resilience often move together.

Rossi made the hormone link explicit when she told Holmes:

"We know that our gut microbes can help actually regulate estrogen, so you may have heard of the term estrobolome. [...] They have a really important role in a lot of women’s health conditions, whether it is something like PCOS, polycystic ovary syndrome, or whether it is like going through menopause."

What you should take away

• A healthy gut shows up through digestion, sleep quality, stress tolerance, immune resilience, and mental health.
• Gut health is modifiable, which means food, sleep, stress management, and movement can all shift the picture over time.
• Hormone changes can affect gut function, and gut microbes also help regulate estrogen metabolism.
• Digestive symptoms are useful signals, but they are only one part of gut health.

If you want to hear Rossi unpack how clinicians define a healthy gut, listen to the full episode on Spotify

How much can gut tests actually tell you right now?

Once the definition is clear, the next question is measurement. Rossi’s view is that current commercial gut tests can be interesting, but they still have major limits.

Her first reason is scientific. Most gut testing still focuses on bacteria, even though the microbiome also includes viruses and fungi that interact with those bacteria. Her second reason is functional. Knowing which microbes are present is less useful than knowing what they are doing, because the same bacteria can behave differently in different gut environments. In Rossi’s words, identical bacteria in two people can act in anti-inflammatory or pro-inflammatory ways depending on context.

That is why Rossi’s research at King’s College London looks beyond names on a stool report and toward metabolites, the compounds microbes produce as they process food. She described work from her lab showing that volatile organic compounds, rather than bacterial names alone, were better at predicting how people responded to dietary or probiotic interventions.

She also pointed Holmes to a 6-year Stanford Medicine microbiome study that followed 86 people and found that healthy microbiomes were highly individualized. The important pattern was not uniformity. It was resilience and stability over time.

Rossi summarized the current gap this way:

"There’s still, I would say, like 30% of our microbiome, which we actually have no idea what these microbes are called, what they’re actually doing."

For now, gut tests work better as snapshots than as final answers. If you want a more useful real-world read, Rossi suggested looking at symptom patterns, sleep, stress, medication use, diet quality, and whether your digestion stays stable over time.

What you should take away

• Commercial gut tests are limited because they usually focus on bacteria and miss much of the microbiome’s viral, fungal, and functional activity.
• Metabolites may prove more useful than bacterial names for predicting how a person responds to food or probiotics.
• A healthy microbiome appears to be individualized, which means there is no single perfect gut profile to chase.
• Stability over time is one of the most useful signals researchers are seeing so far.

If you want to hear Rossi go deeper on why commercial gut tests can overpromise, watch the full episode on YouTube

How are gut health and HRV connected?

From measurement, the conversation naturally moves to physiology. Rossi sees the relationship between gut health and HRV as plausible, useful, and still developing.

Holmes brought up research linking lower heart rate variability to gut dysbiosis, a term used for an imbalanced gut microbiome. Rossi’s explanation centered on the gut-brain axis. The gut and brain communicate through the enteric nervous system and the vagus nerve, through immune signals that can increase inflammation, and through microbe-produced compounds such as short-chain fatty acids that may influence the brain and hormone regulation.

That makes HRV relevant in a practical sense. If WHOOP data shows your HRV staying low and your Recovery staying under pressure even when training load looks reasonable, gut-related stressors may deserve attention alongside sleep and training. Rossi did not present HRV as a direct gut diagnostic. She framed it as one useful signal inside a wider pattern.

She also described clinical work from her team’s psychologist showing that gut-directed hypnotherapy, gut-directed yoga flows, and breathing practices can reduce gut symptoms while also affecting the same stress pathways that shape autonomic flexibility. That is one reason the gut-HRV conversation is worth following. For a related discussion of brain health, exercise, and recovery, read Episode 200 with Dr. Tommy Wood.

Rossi explained the connection to Holmes like this:

"Our brain and our gut constantly communicating via what is known as the enteric nervous system. People probably heard of the vagus nerve, you know, hundreds of millions of nerves innervating and connecting the two."

What you should take away

• HRV may reflect part of the gut-brain connection, especially when stress, inflammation, and recovery are all in play.
• Lower HRV is associated with gut dysbiosis in emerging research, although HRV alone is not a gut health test.
• WHOOP HRV trends can be useful when they are interpreted alongside sleep, recovery, stress, diet, and symptoms.
• Breathing, gut-directed relaxation work, and better stress regulation can support both digestion and autonomic recovery.

If you want to hear Rossi unpack how gut health may show up in HRV and dysbiosis, listen to the full episode on Spotify

What foods actually support a healthier gut?

When Holmes asked what people should actually eat, Rossi’s answer centered on diversity. The strongest pattern in the research is that people who eat a wider variety of plants tend to have healthier gut microbiomes than people who rotate the same few foods.

Rossi’s practical framework is the “Super 6”: legumes, vegetables, fruit, whole grains, nuts and seeds, and herbs and spices. Her logic is straightforward. Each plant carries its own mix of fibers and phytochemicals, and different microbes prefer different foods. If you only feed a narrow slice of your microbiome, you limit the range of functions it can perform.

She urged people to think in weekly variety, not daily perfection. Swapping blueberries for mixed berries, choosing a seed mix over one single seed, and rotating grains all push the microbiome toward greater breadth. Rossi also called out fermented dairy and oily fish as useful additions. Fermented dairy brings bioactive compounds created during fermentation, while oily fish appears to support the microbiome enough that Rossi advises an omega-3 supplement if a person rarely eats salmon, sardines, mackerel, anchovies, or herring.

Her view on grains is also more precise than the usual internet debate. Rossi does not treat gluten as a universal problem. Her concern is that many people eat too many gluten-containing grains and too few other whole grains, which limits variety. That same theme runs through Episode 306 with Dr. Michael Greger, Episode 178 with Dr. Julie Foucher, and Episode 157 with Dr. Hazel Wallace.

Rossi is also studying emulsifiers, a category of food additives found widely in packaged food. Her team’s work is still in progress, and her advice stayed measured: focus first on adding more beneficial foods rather than trying to create a zero-tolerance food rulebook.

Rossi gave Holmes the clearest target of the conversation here:

"What I would say is just thinking, what is one thing that you could then implement? You know, is it just focusing on that plant diversity, you know, getting in at least 30, if not more, different types in a week?"

What you should take away

• Plant diversity is one of the strongest diet signals for a healthier gut microbiome.
• Rossi’s Super 6 framework includes legumes, vegetables, fruit, whole grains, nuts and seeds, and herbs and spices.
• Fermented dairy and oily fish can add useful compounds that support gut health.
• Weekly variety matters more than chasing one superfood or cutting out large categories of food without a clear reason.

If you want to hear Rossi go deeper on plant diversity, grains, and food additives, watch the full episode on YouTube

How do sleep and stress shape the gut-brain connection?

Food is one lever, but Rossi repeatedly returned to sleep and stress as equally important pillars. A gut-friendly diet can only go so far if sleep is poor and stress stays high.

Rossi cited research showing that two nights of sleep deprivation, with participants getting around four to five hours of sleep, changed the microbiome. She also mentioned a probiotic study that improved sleep duration, which supports the idea that the sleep-gut relationship runs both ways. Her explanation was simple: gut microbes follow circadian rhythms too. If sleep quantity, sleep quality, or sleep consistency is off, the microbiome loses some of the recovery window it depends on.

Stress works through the same network. Butterflies before a big event are a familiar example of top-down signaling from the brain to the gut. At a clinical level, Rossi pointed to irritable bowel syndrome, or IBS, as a case where gut-brain communication becomes dysregulated. The Rome Foundation defines IBS as a disorder of gut-brain interaction, and Rossi noted that chronic stress and trauma can be part of the picture.

Her practical advice was refreshingly basic and still evidence-based: use a sleep routine, get light exposure soon after waking, keep meals sensible before bed, write worries down before sleep, do five minutes of diaphragmatic breathing before meals if digestion is reactive, and slow down enough to chew food properly. Rossi said better chewing can raise nutrient absorption, citing work showing a clear difference between fewer chews and more thorough chewing.

Rossi gave Holmes a tight summary of the sleep link:

"After 2 nights of sleep deprivation, I think the clinical trial used, it was like 4 or 5 hours of sleep, actually their microbiome started to change."

What you should take away

• Sleep loss can alter the microbiome quickly, which makes sleep duration, quality, and consistency relevant to gut health.
• Gut microbes follow circadian rhythms, so irregular sleep can disturb gut recovery.
• IBS is increasingly understood as a disorder of gut-brain interaction, not only a food problem.
• Diaphragmatic breathing before meals and slower chewing can reduce digestive stress and improve nutrient handling.

Do probiotics, supplements, and exercise improve gut health?

By the end of the conversation, Holmes pushed into the interventions people often ask about first. Rossi’s answer was nuanced: exercise usually helps, while supplements need to be specific.

On training, Rossi said the best evidence currently points to endurance-style exercise. Research suggests that exercising about three times per week at moderate to high intensity is associated with a more diverse microbiome, even independent of diet. The mechanism is still being worked out. Rossi mentioned several candidates, including changes in gut motility, more exposure to outdoor microbes, and the possibility that lactate itself can feed certain beneficial bacteria.

That last point connects to one of the most interesting athletic findings in the field. Rossi referenced research on Boston Marathon runners whose microbiomes contained bacteria especially good at metabolizing lactate. Follow-up animal work on Veillonella atypica and exercise performance found about a 13% improvement in treadmill performance, which hints at how tightly gut function and performance biology can intersect.

Supplements, in her view, should be used with the same precision. Rossi does not recommend taking a general probiotic every day for vague “gut health.” She does recommend specific probiotics for specific cases. Her clearest example was antibiotic use, where she said the evidence supports Lactobacillus rhamnosus GG at 10 billion units twice daily during antibiotics and for one week after. By contrast, she sees little support for broad-spectrum digestive enzyme blends unless there is a clear medical reason, such as pancreatic insufficiency.

Rossi put the probiotic point in concrete terms:

"There’s really good evidence and it’s guidelines that you should take a specific probiotic called Lactobacillus rhamnosus GG. You would take it at 10 billion units twice a day throughout your antibiotic period and for a week after."

What you should take away

• Exercise is associated with a more diverse microbiome, with the clearest evidence currently coming from endurance-style training.
• Gut microbes may influence performance partly through how they process lactate and other exercise-related metabolites.
• Probiotics work best when they are matched to a specific need, not when they are treated as a general daily shortcut.
• Broad-spectrum digestive enzyme supplements have weak support for routine use outside clear medical indications.

The bottom line

• A healthy gut is defined by function, including regular digestion, better sleep, steadier stress tolerance, and fewer signs of immune strain.
• Current commercial gut tests can be interesting, but today’s science still misses much of the microbiome’s viral, fungal, and metabolic activity.
• Gut health and HRV are connected through the gut-brain axis, inflammatory signaling, and microbe-produced compounds, which makes HRV one useful signal inside a larger picture.
• Plant diversity is one of the strongest diet levers for gut health, and Rossi’s practical target is at least 30 different plant foods per week.
• Fermented dairy, oily fish, and a wider variety of whole grains can support the gut without turning the diet into a restrictive project.
• Sleep quantity, sleep quality, and sleep consistency all affect the gut, and even short periods of sleep deprivation can shift the microbiome.
• Stress management matters because digestion is shaped by the same gut-brain pathways that influence sleep, HRV, and day-to-day recovery.
• Probiotics and digestive supplements make the most sense when they are used for a clear reason, with a specific strain, dose, and timeline.

Frequently asked questions about things discussed in this episode

How does WHOOP measure heart rate variability?

WHOOP measures heart rate variability during sleep, when the body is more stable, which makes overnight HRV a useful way to track changes in autonomic recovery alongside stress, illness, sleep loss, and other gut-related strain.

What does WHOOP show about sleep consistency and gut health?

WHOOP shows sleep consistency through your timing patterns, and regular sleep timing matters because gut microbes follow circadian rhythms that can shift when sleep becomes irregular.

How can WHOOP help you spot whether diet changes are helping your gut?

WHOOP helps you spot patterns by pairing trends in Recovery, HRV, Sleep, and resting heart rate with changes you log around food variety, meal timing, alcohol, and training load.

What does WHOOP track that can reflect stress affecting digestion?

WHOOP tracks HRV, resting heart rate, Sleep, and Recovery trends, and changes across those metrics can surface accumulating stress that may also be showing up as digestive symptoms.

How does WHOOP support better recovery when you start eating more fiber or more plants?

WHOOP supports that transition by showing whether sleep quality, recovery patterns, and strain tolerance stay stable as your diet changes, which can help separate short-term adjustment from broader overload.

What can WHOOP tell you if your HRV stays low even when training looks normal?

WHOOP can show that low HRV is persisting even when Strain is steady, which can point you toward other levers discussed in this episode, including sleep regularity, stress load, digestive symptoms, and diet quality.

For questions like whether a harder training block, a week of poor sleep, or a less varied diet is showing up in your recovery, WHOOP helps make the gut-performance connection easier to see.