Water is an essential component of life, comprising around 60% of an average adult human’s body. It takes part in all the major physiological processes, from regulating temperature to lubricating joints, transporting nutrients, and removing waste products. One of the vitally important, but often overlooked, roles of water is in supporting digestion. When we consume food and drink, a series of mechanical, chemical, and biochemical processes help transform it into usable nutrients for the body, whilst eliminating waste.
In this article, we will examine how water supports each phase of digestion, the signs and consequences of dehydration on gut health, practical guidelines for optimal hydration, and common misconceptions.
The Role of Water in Digestion
The Mouth
Food undergoes a complex, multifaceted digestive journey, starting with chewing in the mouth and ending with its eventual elimination as waste. Throughout every stage of this trek, water acts as a medium, a solvent, and a lubricant [1,2]. The enzymes required for digestion work in an aqueous environment [3], which helps break down carbohydrates, proteins, and fats. Water also dissolves micronutrients (vitamins and minerals) as well as other small molecules, allowing their transport through the intestinal walls. Not only that, but water-based secretions keep food moving through the digestive tract and protect delicate tissues from mechanical damage [2]. Without adequate hydration, these fundamental processes become inefficient, leading to a cascade of digestive issues.
Digestion begins the moment we put food in our mouths. Saliva, which is about 98% water, contains amylase, lipase, and mucins. Amylase is an enzyme that begins the process of digesting starch, whereas lipase helps break down certain fats. Mucins create a slippery mucus that allows food to make a cohesive bolus.
When you’re dehydrated, saliva production drops. Dry mouth (xerostomia) not only makes chewing and swallowing uncomfortable but also slows the enzymatic initiation of digestion. A poorly formed bolus can increase the risk of choking and contribute to dysphagia (difficulty swallowing). For athletes, busy professionals, or anyone on the go, even mild dehydration can compromise this first critical step of the digestive process.
The Stomach
Once swallowed, the food bolus enters the stomach, where it encounters gastric juice. This is a mixture of hydrochloric acid, pepsin (a protein-digesting enzyme), intrinsic factor, and mucus. Over 90% of gastric juice is water, and it serves to unravel and cleave proteins, kill or inhibit any ingested pathogens, and produce a semi-liquid mass called chyme that is ready to enter the small intestine.
Dehydration can lead to reduced gastric volume and lower acid secretion, impairing protein digestion and increasing susceptibility to indigestion, bloating, or gastroesophageal reflux. Furthermore, insufficient fluid can alter stomach motility, leading to delayed gastric emptying and discomfort, especially during physical activity [4].
The Small Intestine
The small intestine is where the bulk of nutrient breakdown and absorption takes place. It receives pancreatic juice that is rich in enzymes and fluid, as well as bile. Here, water helps maintain a proper aqueous environment so that enzymes can diffuse through and access substrates. It also supports optimal pH levels for good enzyme activity and aids in the transport of nutrients across enterocytes (intestinal cells).
When hydration is poor, nutrient absorption efficiency declines. Essential vitamins, electrolytes, and macronutrients may pass through unabsorbed, potentially leading to deficiencies over time.
The Colon
By the time chyme reaches the large intestine, it contains indigestible residues, bacteria, and a mix of water and electrolytes. The colon’s primary functions are to reabsorb water (around 1-1.5 L) to maintain fluid balance, condense waste material into stools, and assist in the fermentation of some fibers.
Dehydration hampers water reabsorption balance. Too little water in the lumen leads to hard, dry stools and constipation. Conversely, overly rapid transit with insufficient water uptake can result in loose stools or diarrhea, both impairing nutrient and fluid balance. Chronic constipation can contribute to hemorrhoids, anal fissures, and diverticular disease, making hydration a frontline defense here.
Implications of Dehydration for Digestive Health
Digestive-specific symptoms of dehydration often overlap with general dehydration signs but have a gastrointestinal focus: a dry, sticky mouth and reduced saliva; thick mucus or hoarseness; bloating, cramping, or a feeling of fullness; constipation, hard stools, or infrequent bowel movements; heartburn or acid reflux; and nausea or reduced appetite.
Long-term or severe dehydration can exacerbate gastroenterological disorders such as irritable bowel syndrome, gastritis, and ulcers, as well as kidney stones.
Fiber, Water, and Digestive Synergy
Dietary fiber, both soluble and insoluble, is celebrated for its beneficial effects on digestion, but its efficacy is tied directly to hydration. Soluble fiber dissolves in water to form a gel, slowing gastric emptying and stabilizing blood glucose (sugar) levels. Insoluble fiber attracts water into the colon, increasing stool bulk and promoting regularity.
Without sufficient water, fiber can bind up residual fluids in the gut, worsening constipation rather than alleviating it. Therefore, any increase in dietary fiber should be accompanied by a corresponding increase in fluid intake to maintain stool softness and promote healthy bowel function.
Hydration and the Gut Microbiome
The gut microbiome is a vast ecosystem of bacteria, fungi, and other microorganisms. It plays a pivotal role in digestion, immunity, and even mental health. Adequate hydration supports this ecosystem by maintaining mucosal integrity, facilitating metabolite transport, and preventing pathogen overgrowth [5,6].
Chronic low-grade dehydration may shift microbial balance toward less beneficial species, potentially contributing to inflammatory bowel conditions, autoimmune disorders, and metabolic dysregulation.
Practical Guidelines for Optimal Hydration
Hydration needs are individual, influenced by age, activity level, climate, diet, and health status. A classic rule is to consume 1 mL of fluid for every kcal of food energy consumed. The European Food Safety Authority recommends 1.6 L/day for females and 2.0 L/day for males [7].
While plain water is ideal, all non-diuretic fluids (e.g., herbal teas, diluted fruit juices) and high-fluid content foods count towards hydration goals.
Thirst is a late indicator of fluid depletion [8]. This is especially so the older we get [9,10]. Thirst also tends to be alleviated before full rehydration is achieved [11]. Regular, mindful drinking better prevents the subtle gastrointestinal impacts of mild dehydration. Additionally, when we are thirsty, we tend to overestimate the volume of cold and carbonated (fizzy) drinks that we ingest [12], so consider this.
Conclusion
Maintaining adequate hydration is far more than quenching your sensation of thirst. It’s a cornerstone of overall health. Water acts as the medium for enzymatic reactions, the solvent for nutrient absorption, and the lubricant that keeps food moving smoothly throughout the gastrointestinal tract. From reducing constipation and acid reflux to nurturing a balanced gut microbiome, ample hydration safeguards against a host of digestive complaints and chronic conditions.
If you're interested in learning more about gut health and the gut microbiome, check out the blogs below:
References
[1] U. Laforenza, Water channel proteins in the gastrointestinal tract, Molecular Aspects of Medicine 33 (2012) 642–650. https://doi.org/10.1016/j.mam.2012.03.001.
[2] B.M. Popkin, K.E. D’Anci, I.H. Rosenberg, Water, hydration, and health, Nutrition Reviews 68 (2010) 439–458. https://doi.org/10.1111/j.1753-4887.2010.00304.x.
[3] J.R. Ross, M.M. Shaw, THE EFFECT OF DEHYDRATION ON THE PANCREATIC AND INTESTINAL ENZYMES, Journal of Biological Chemistry 104 (1934) 131–139. https://doi.org/10.1016/S0021-9258(18)75799-2.
[4] M.A. Van Nieuwenhoven, B.E.P.J. Vriens, R.-J.M. Brummer, F. Brouns, Effect of dehydration on gastrointestinal function at rest and during exercise in humans, European Journal of Applied Physiology 83 (2000) 578–584. https://doi.org/10.1007/s004210000305.
[5] K. Sato, M. Hara-Chikuma, M. Yasui, J. Inoue, Y.-G. Kim, Sufficient water intake maintains the gut microbiota and immune homeostasis and promotes pathogen elimination, iScience 27 (2024) 109903. https://doi.org/10.1016/j.isci.2024.109903.
[6] T. Vanhaecke, O. Bretin, M. Poirel, J. Tap, Drinking Water Source and Intake Are Associated with Distinct Gut Microbiota Signatures in US and UK Populations, The Journal of Nutrition 152 (2022) 171–182. https://doi.org/10.1093/jn/nxab312.
[7] O. Masot, J. Miranda, A.L. Santamaría, E. Paraiso Pueyo, A. Pascual, T. Botigué, Fluid Intake Recommendation Considering the Physiological Adaptations of Adults Over 65 Years: A Critical Review, Nutrients 12 (2020) 3383. https://doi.org/10.3390/nu12113383.
[8] E.L. Kenney, M.W. Long, A.L. Cradock, S.L. Gortmaker, Prevalence of Inadequate Hydration Among US Children and Disparities by Gender and Race/Ethnicity: National Health and Nutrition Examination Survey, 2009–2012, Am J Public Health 105 (2015) e113–e118. https://doi.org/10.2105/AJPH.2015.302572.
[9] L. Hooper, D.K. Bunn, A. Downing, F.O. Jimoh, J. Groves, C. Free, V. Cowap, J.F. Potter, P.R. Hunter, L. Shepstone, Which Frail Older People Are Dehydrated? The UK DRIE Study, GERONA 71 (2016) 1341–1347. https://doi.org/10.1093/gerona/glv205.
[10] S. Li, X. Xiao, X. Zhang, Hydration Status in Older Adults: Current Knowledge and Future Challenges, Nutrients 15 (2023) 2609. https://doi.org/10.3390/nu15112609.
[11] R.W. Kenefick, Drinking Strategies: Planned Drinking Versus Drinking to Thirst, Sports Med 48 (2018) 31–37. https://doi.org/10.1007/s40279-017-0844-6.
[12] C. Peyrot Des Gachons, J. Avrillier, M. Gleason, L. Algarra, S. Zhang, E. Mura, H. Nagai, P.A.S. Breslin, Oral Cooling and Carbonation Increase the Perception of Drinking and Thirst Quenching in Thirsty Adults, PLoS ONE 11 (2016) e0162261. https://doi.org/10.1371/journal.pone.0162261.
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