If constipation were simply caused by not eating enough fibre, the solution would be straightforward: eat more fibre and wait for things to move.
But your bowel doesn't work in isolation.
Bowel movements depend on a whole system, including the amount of water available to the stool, physical activity, meal-related signals, the coordination of the pelvic floor, your nervous system and even the metabolic activity of the bacteria living in your gut.
That is why two people can eat a very similar diet and have completely different bowel habits.
1. Using fluid to keep things moving: fibre needs the right environment to work
“I’m eating more fibre and now I’m bloated and constipated” - sound familiar? One of the first things to consider when constipation is an issue is fluid intake.
Your colon absorbs water from the contents passing through it. As stool spends longer in the colon, more water can be removed, which can contribute to harder, drier stools that are more difficult to pass.
But this doesn't mean that “the more water you drink, the better you'll poo.”
Hydration is more relevant when someone isn't drinking enough to begin with, and the relationship becomes particularly interesting when fibre intake increases. If you think about fibre bulking up your stool, you need water and liquid to support with softening it to keep things moving along nicely.
One clinical trial involving adults with chronic functional constipation found that increasing fluid intake alongside a fibre intake of around 25 g/day improved stool frequency and reduced laxative use more than fibre intake alone. (1)
The takeaway: If you're increasing fibre pay attention to your fluid intake. More fibre requires more hydration in order for things to actually move on.
2. Movement: your gut likes movement too
We often think about exercise in terms of our muscles, heart and metabolism, but movement may also support digestive function. A simple walk can help massage the digestive tract and move food through.
Physical activity appears to have a positive effect on bowel function, and research suggests that regular exercise can help improve constipation symptoms in some people. (2)
For someone who spends much of the day sitting, simply walking more, breaking up periods of sitting and being consistently active may be a useful part of supporting healthy bowel function.
3. Regular and consistent meal times: eating actually tells your colon to move
You might assume that if you're constipated, eating less will give your digestive system a break.
But eating is actually one of the signals that can stimulate colonic activity.
It's known as the gastrocolic response, essentially, when food enters the stomach, signals are generated that can increase motor activity in the colon.
A review of the gastrocolic response describes an increase in colonic motor activity that usually occurs within minutes of eating. Gastric distension, calories and the fat content of a meal can all influence this response, which is mediated through neural and hormonal pathways. (3)
This helps explain why you might suddenly feel the urge to go after breakfast or another meal.
There's a second, complementary mechanism at play between meals: the migrating motor complex (MMC). This is a wave of electrical activity that sweeps through the stomach and small intestine during periods of fasting, clearing leftover food debris and bacteria through to the colon. It typically kicks in around two to three hours after your last meal, once digestion has settled. The moment you eat again, even a small snack, this sweeping action switches off and digestion restarts.
This is part of why we tend to encourage proper breaks between meals rather than grazing throughout the day. Constant snacking keeps the gut in a fed state and doesn't give the MMC the chance to complete its sweep, which over time may contribute to sluggish digestion and bacterial overgrowth in the small intestine.
If you're constantly skipping meals, eating very irregularly or ignoring your body's signals, you're potentially missing opportunities for these normal digestive reflexes.
Regular and consistent eating and timings can provide regular physiological signals to your digestive system.
For some people, making breakfast and the morning routine a consistent part of their day can create a useful opportunity to respond to the body's natural gastrocolic response.
4. Your pelvic floor matters too
Here's another reason why constipation isn't always a fibre problem. Passing stool requires more than simply producing a bowel movement.
Your abdominal muscles, rectum and pelvic floor need to coordinate properly to allow evacuation.
For some people with chronic constipation, particularly those experiencing difficulty evacuating despite having the urge, the issue can involve problems with pelvic-floor coordination or defecatory disorders.
You will often hear that putting your feet on a small stool, also known as a Squatty Potty, that can mimic a squatting position and make bowel movements easier.
There's a physiological rationale for this - raising the feet changes hip and trunk position.
5. Your nervous system and your gut are constantly talking
Your digestive system isn't simply a long tube processing food.
It has its own extensive nervous system, the enteric nervous system (ENS) which coordinates many aspects of gastrointestinal function, including movement.
And it is constantly communicating with the brain.
This is why stress can affect your gut.
Research into the gut-brain axis has demonstrated that psychological stress can influence gastrointestinal motility, secretion and visceral sensitivity. In people with disorders such as IBS, stress can also amplify gastrointestinal symptoms and alter patterns of gut motility. (4)
This is why some people notice their bowel habits change when they're:
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travelling
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under pressure at work
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sleeping badly
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going through a stressful period
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rushing meals
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out of their normal routine
The gut and brain are physically and chemically connected. A resilient digestive system isn't one that never responds to stress. It's one that can adapt to changes in food, routine, stress and environment without symptoms becoming overwhelming or persistent.
6. And then there's your gut microbiome...
Your gut is home to trillions of bacteria, and we're increasingly understanding that your gut microbes and bowel movements are connected in both directions.
The bacteria living in your gut produce compounds such as short-chain fatty acids (SCFAs) when they ferment fibre and carbohydrates. These compounds can communicate with cells in the gut and may influence the signals involved in intestinal movement and motility. (5)
There are also links between the microbiome, bile acids and serotonin, all of which can play a role in how your gut moves.
So, in simple terms:
What you eat → your gut bacteria → microbial metabolites → signals to your gut → bowel movement.
Research has also found differences in the gut microbiome of people with constipation, including changes in certain bacterial groups and increased methane production. However, we don't yet know that there's one specific “constipation bacteria” that needs to be added or increased. (6)
The takeaway? Your gut microbiome is part of the bigger picture when it comes to healthy bowel function. Supporting your gut isn't simply about eating more fibre — it's about creating the conditions for your whole digestive ecosystem to thrive.
A healthy gut isn't about having perfect digestion every single day. It's about creating the right conditions for your gut to move, adapt and respond — through nourishing food, enough fluid, movement, regular routines, and supporting your gut microbiome. Small, consistent habits can make a bigger difference
References
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Anti M, Pignataro G, Armuzzi A, Valenti A, Iascone E, Marmo R, Lamazza A, Pretaroli AR, Pace V, Leo P, Castelli A, Gasbarrini G. Water supplementation enhances the effect of high-fiber diet on stool frequency and laxative consumption in adult patients with functional constipation. Hepatogastroenterology. 1998 May-Jun;45(21):727-32. PMID: 9684123.
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Gao R, Tao Y, Zhou C, Li J, Wang X, Chen L, Li F, Guo L. Exercise therapy in patients with constipation: a systematic review and meta-analysis of randomized controlled trials. Scand J Gastroenterol. 2019 Feb;54(2):169-177. doi: 10.1080/00365521.2019.1568544. Epub 2019 Mar 7. PMID: 30843436.
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Dorfman L, El-Chammas K, Mansi S, Kaul A. Gastrocolonic Response. Curr Gastroenterol Rep. 2022 Nov;24(11):137-144. doi: 10.1007/s11894-022-00849-2. Epub 2022 Nov 3. PMID: 36324042.
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Schaper SJ, Stengel A. Emotional stress responsivity of patients with IBS - a systematic review. J Psychosom Res. 2022 Feb;153:110694. doi: 10.1016/j.jpsychores.2021.110694. Epub 2021 Dec 14. PMID: 34942583.
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Vicentini FA, Fahlman T, Raptis SG, Wallace LE, Hirota SA, Sharkey KA. New Concepts of the Interplay Between the Gut Microbiota and the Enteric Nervous System in the Control of Motility. Adv Exp Med Biol. 2022;1383:55-69. doi: 10.1007/978-3-031-05843-1_6. PMID: 36587146.
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Dimidi E, Christodoulides S, Scott SM, Whelan K. Mechanisms of Action of Probiotics and the Gastrointestinal Microbiota on Gut Motility and Constipation. Adv Nutr. 2017 May 15;8(3):484-494. doi: 10.3945/an.116.014407. PMID: 28507013; PMCID: PMC5421123.
