Written by Dr Jafar Jafari, GI Cognition
This article reflects the opinions of a healthcare professional. The views expressed are their own. The intended use for the GastroCH4ECK® is to aid in the diagnosis of the following disorders:
- Lactose Intolerance,
- Small Intestinal Bacterial Overgrowth (SIBO).
Hydration and nutrition are often discussed as two separate topics. In reality, they work together every single day inside the digestive system. What we drink influences how comfortably we tolerate fibre, how easily our bowels move, and how efficiently our digestive system works. What we eat influences digestion, gas production, stool pattern, energy levels, and symptoms such as bloating or abdominal discomfort.
A simple way to think about this relationship is to imagine trying to mix ingredients in a completely dry container. Nothing moves properly. The contents simply sit there. Digestion works in a similar way: without adequate fluid, the digestive system struggles to move food smoothly through the gut. Hydration provides the medium in which digestion happens, while nutrition provides the materials the body, and the microbes in our gut, need to function.
But how do we know whether our gut is responding well to what we eat and drink? Interestingly, one of the most informative signals can come from something we rarely think about: our breath.
Your Breath as a “Thermometer” for the Gut1
One of the reasons I became so interested in hydrogen–methane breath testing (HMBT), and ultimately wrote a book about it The Essential Guide to Hydrogen and Methane Breath Testing, the book offers a unique window into how our digestive system is functioning.
Human tissues do not produce hydrogen or methane gases. These gases are produced when microorganisms in the gut ferment carbohydrates that escape digestion. Some of this gas enters the bloodstream and eventually reaches the lungs, where it is exhaled in our breath. By measuring hydrogen and methane in breath samples over time, clinicians can gain insight into microbial fermentation patterns in the gut.
In a way, breath testing acts like a thermometer for gut activity. Just as a thermometer shows how the body is responding to infection or inflammation, breath testing can reveal how gut microbes are responding to the food and drink we consume.
The interesting point is that this signal often appears much earlier than other markers of health. For example, nutritional deficiencies such as low iron or low vitamin B12 can take months or even years to develop before they are detected in blood tests. But changes in microbial fermentation can occur much more quickly, reflecting the daily interaction between diet, hydration, gut motility and microbial activity.
In that sense, microbial fermentation may provide one of the earliest signals that something in our digestive habits is not working well.
Why “Healthy Foods” Sometimes Cause Symptoms
One of the most common questions people ask is: “Why do I react to foods that are supposed to be healthy?”
- The answer is surprisingly simple: healthy does not always mean symptom-free.
Foods such as fruit, beans, lentils, whole grains and many vegetables are rich in fibre and nutrients2. These foods are beneficial for long-term health and support the growth of beneficial microbes in the gut.
However, they are also fermentable. For people with slower gut movement, increased microbial activity in the small intestine, or heightened gut sensitivity, fermentation of these foods may produce more gas than the body comfortably tolerates1.
This does not mean those foods are harmful or should be permanently avoided. It simply means that digestion sometimes requires a more personalised approach, including attention to portion size, timing, food combinations and underlying digestive function. Understanding these patterns is where breath testing can sometimes be helpful.
Hydration: The Forgotten Partner of Fibre
Another question I frequently hear is whether drinking more water can help symptoms such as constipation or bloating. Hydration alone is rarely a complete solution, but it plays a crucial role in maintaining normal digestive function.
Adequate fluid intake supports healthy bowel movement and gut motility. When the body is dehydrated, the intestines absorb more water from the stool, making it harder and more difficult to pass.
Hydration also becomes particularly important when people increase fibre intake. Fibre and fluid work together. Increasing fibre rapidly without increasing fluid can sometimes make symptoms feel worse, especially in people with sensitive digestive systems.
For most adults, general NHS guidance suggests roughly 6 to 8 glasses of fluid per day3, though individual needs vary depending on activity level, environment and health status. A simple daily indicator of hydration is urine colour, pale yellow generally indicates adequate hydration3.
Another useful indicator of digestive health is the Bristol stool chart4, which describes stool consistency. It is a simple but surprisingly helpful way of monitoring how well the digestive system is functioning4.
These simple daily observations, hydration, stool pattern, and symptoms, can act as basic “thermometers” of gut health. Breath testing simply provides a more advanced version of this thermometer, offering deeper insight into microbial fermentation patterns, when the basic thermometers are not sufficient anymore1.
Why Testing Before Treatment Matters1
When people experience persistent digestive symptoms, they often feel tempted to experiment with probiotics, restrictive diets, or various supplements. Trying something new can feel proactive. However, in some situations this approach may not address the underlying cause and can occasionally make symptoms worse.
For example, if someone already has excessive microbial activity in the small intestine, adding more bacteria through probiotics may not always be beneficial. Similarly, eliminating large groups of foods without a clear reason can lead to unnecessary dietary restriction and reduced nutritional balance.
Restrictive diets may sometimes reduce symptoms temporarily, but they can also reduce the intake of important nutrients such as fibre, vitamins and minerals, all of which support long-term gut and overall health. In addition, overly restrictive eating patterns may deprive the beneficial microbes in the gut of the nutrients they rely on for their normal activity and balance.
A more rational approach is to test first, understand the underlying mechanism, and then treat accordingly. This is where tools such as hydrogen–methane breath testing can provide valuable information5,6.
Breath testing should always be interpreted carefully within the clinical context, to ensure accurate results5,6. It remains the only validated clinical test that provides a functional assessment of microbial fermentation activity in the gut1. Unlike many emerging microbiome analyses, which are currently not standardised or reliable enough to guide treatment decisions, breath testing can help identify patterns such as carbohydrate malabsorption, abnormal fermentation, or possible bacterial overgrowth when used appropriately.
These insights can guide more targeted management rather than trial-and-error approaches, especially, if you are really suffering from the symptoms.
A Note on IBS, Stress and Unexplained Symptoms7
Another important point is that conditions such as irritable bowel syndrome (IBS) must be considered as diagnoses of exclusion. In practice, this means that when major structural or inflammatory diseases have been ruled out, completely, then, symptoms may be grouped under the IBS label.
However, this does not mean the symptoms are imaginary or simply due to stress. While stress can influence gut function, it is often too simplistic to attribute persistent symptoms to psychological factors alone. In practice, almost any symptom can be linked to stress if we stop looking for other explanations! In the same way, many gut symptoms can quickly be labelled as IBS!
In many cases, subtle physiological mechanisms, such as altered gut motility, microbial fermentation, gut hypersensitivity, or food intolerance, may be contributing to symptoms even when routine tests appear normal1. Advances in gut physiology and microbiome research are gradually helping us understand these mechanisms better.
Practical Advice for Hydration and Nutrition Week
For Hydration and Nutrition Week, my message is simple.
- Drink fluids regularly throughout the day rather than all at once3.
Use urine colour as a simple guide to hydration.
- Include fibre in your diet but increase it gradually to avoid developing symptoms2.
Use stool pattern as a simple guide to fibre intake.
- If you have persisting symptoms despite eating and drinking well, consider whether there may be an underlying reason that deserves further investigation1.
Use Hydrogen-Methane Breath Test as a validated medical grade guide to the root causes.
Digestive symptoms are rarely random. The body always has a reason for them.
In everyday life we already use simple “thermometers” of gut health, urine colour can suggest hydration, and stool patterns can reflect gut movement. At a deeper level, hydrogen–methane breath testing can act as a functional thermometer of microbial activity and your diet in the gut1.
Sometimes, the answers to persistent digestive symptoms can be found not only in what we eat and drink, but also in what our breath quietly reveals about the inner workings of our gut.
This hydration and nutrition week, take control of your gut health. If you are experiencing persistent gut issues, consult a healthcare professional and ask about breath testing. Hydrogen and methane breath testing (HMBT) with devices like the Gastrolyzer® range offer a non-invasive insight into gut health and can aid investigation or diagnosis in a clinical setting or from the comfort of your own home.
To learn more about the Gastrolyzer® range, visit the website here. Dr Jafari’s book ‘The Essential Guide to Hydrogen and Methane Breath Testing’ covers HMBT in detail, if you would like to learn more visit the webpage here.
References:
- Jafari J. 2025. The Essential Guide to Hydrogen and Methane Breath Testing: The Modern Non-Invasive Approach to Investigating Gastrointestinal Disorders. Bedfont Scientific Ltd, United Kingdom.
- NHS. How to get more fibre into your diet. Available at: https://www.nhs.uk/live-well/eat-well/how-to-get-more-fibre-into-your-diet/ (Accessed: 16th March 2026).
- NHS. Water, drinks and your health. Available at:
https://www.nhs.uk/live-well/eat-well/water-drinks-nutrition/ (Accessed: 16th March 2026).
- Yaseen S, Abuelass FK, kamaleldien mohamed Abuelass F. Improving Documentation of Bowel Movements Using the Bristol Stool Chart: A Quality Improvement Project in a District General Hospital in the United Kingdom. Cureus. 2026 Jan 6;18(1).
- Rezaie A, Buresi M, Lembo A, Lin H, McCallum R, Rao S, Schmulson M, Valdovinos M, Zakko S, Pimentel M. Hydrogen and methane-based breath testing in gastrointestinal disorders: the North American consensus. Official journal of the American College of Gastroenterology| ACG. 2017 May 1;112(5):775-84.
- Pimentel M, Saad RJ, Long MD, Rao SS. ACG clinical guideline: small intestinal bacterial overgrowth. Official journal of the American College of Gastroenterology| ACG. 2020 Feb 1;115(2):165-78.
- National Institute for Health and Care Excellence (NICE). Irritable bowel syndrome in adults: diagnosis and management (CG61). Available at: https://www.nice.org.uk/guidance/cg61 (Accessed: 16th March).
