Digest IT!

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One of the most common and genuinely worrying things I see in my nutrition practice is clients who are drinking litre after litre of plain water during a bout of diarrhoea — and still becoming dangerously dehydrated. They cannot understand why. They are doing what they were told. They are drinking. But the connection between electrolytes, diarrhoea, and rehydration is far more complex than simply topping up fluids, and once you understand what is actually happening inside your body, your entire approach to recovery changes. This is one of those areas where a small shift in knowledge makes an enormous difference to how quickly — and how safely — you recover.

What Diarrhoea Actually Does to Your Body

When you experience diarrhoea, your body is not simply losing water. It is losing a carefully balanced cocktail of minerals — sodium, potassium, chloride, magnesium, and bicarbonate — that your cells depend on to function. These are your electrolytes, and without them, your body cannot maintain fluid balance, nerve signalling, or muscle contraction. Every loose stool can strip away significant quantities of these minerals, and the faster and more frequent the episodes, the more dramatic that loss becomes.

Here is the part that surprises most people: the sodium-glucose cotransport mechanism in your small intestine is what actually drives water absorption. When sodium and glucose are present together in the right ratio, water follows them across the gut wall and into your bloodstream. This is why the World Health Organisation’s oral rehydration solution contains both sugar and salt — not because someone made a mistake, but because the science demands it. Plain water bypasses this mechanism almost entirely. Drinking water without electrolytes during active diarrhoea can actually dilute your remaining sodium levels further, making dehydration worse at a cellular level even as your stomach feels full.

In my practice, I have seen otherwise healthy adults become genuinely unwell after forty-eight hours of a stomach bug, not because they ignored hydration, but because they hydrated incorrectly. Understanding this is the first step to doing it right.

The Science of Oral Rehydration: Why Balance Matters

Oral rehydration therapy, or ORT, is considered one of the most significant public health advances of the twentieth century. The research behind it, much of it developed during cholera outbreaks in the 1960s, established that a precise ratio of sodium, glucose, and water could effectively rehydrate even severely dehydrated patients. The principle scales directly down to everyday gastroenteritis or traveller’s diarrhoea — the biology is the same, the stakes are simply lower.

For most adults managing diarrhoea at home, the goal is to replace what is being lost without overwhelming the gut with concentrated sugars or artificial ingredients. This is where a good electrolyte product becomes genuinely valuable, rather than being a luxury sports supplement. I consistently recommend keeping a supply at home before you need it, because the last thing you feel like doing during a stomach upset is heading out to a pharmacy.

Two products I regularly point clients towards are the Amazon Basic Care Electrolyte Powder Packets in Grape Flavour and the Amazon Basic Care Electrolyte Powder Packets in Orange Flavour. Both are straightforward, accessible options suitable for adults and children, providing the key electrolytes your body needs during fluid loss. For something more clinically focused, the NormaLyte Pure Electrolyte Powder Packets are worth considering — this is a clinically studied formulation specifically designed for effective hydration, and I have recommended it to clients managing chronic digestive conditions as well as acute illness.

Recognising the Signs That Rehydration Is Not Working

Part of my role as a nutritionist is helping clients recognise when their body is telling them something important. Dehydration during diarrhoea is not always obvious, and people often underestimate how quickly it can escalate, particularly in young children, older adults, and anyone with an underlying health condition.

Warning signs that your current approach to rehydration is insufficient include:

• Dark yellow or amber urine, or significantly reduced urination
• Persistent dizziness or lightheadedness, especially when standing
• Muscle cramps, particularly in the legs — a classic sign of low potassium and magnesium
• Dry mouth, sunken eyes, or skin that does not spring back when gently pinched
• Unusual fatigue, confusion, or rapid heart rate
• Continued or worsening symptoms beyond forty-eight to seventy-two hours

If several of these are present, particularly in a vulnerable individual, please seek medical attention promptly. No nutritional intervention replaces emergency medical care when it is genuinely needed.

That said, for the majority of otherwise healthy adults experiencing a standard acute episode, proper electrolyte rehydration alongside rest and careful food reintroduction will bring significant improvement within twenty-four to forty-eight hours. The gut is remarkably resilient when we give it the right support.

Supporting Gut Recovery: Beyond Rehydration

Once the acute phase begins to ease and you are keeping fluids down reliably, the focus can shift to gut recovery. This is where I see a lot of people stall — they feel a little better, return to their normal diet too quickly, and trigger a second wave of symptoms. The intestinal lining needs time and targeted support to restore its function after a bout of diarrhoea, particularly if it was caused by infection or food poisoning.

Two areas I prioritise with clients in recovery are the microbiome and stool consistency.

Restoring the Microbiome with Probiotics

Diarrhoea, especially when accompanied by antibiotic treatment, can significantly deplete the beneficial bacteria in your gut. Replenishing these with a well-researched probiotic is one of the most evidence-supported steps you can take during recovery. The Lactobacillus rhamnosus GG strain in particular has been extensively studied for its role in shortening the duration of infectious diarrhoea and reducing recurrence.

I often recommend Culturelle Daily Probiotic Capsules, which contain the most clinically studied probiotic strain available and provide a full month’s supply. For clients who need longer-term gut rehabilitation — particularly those recovering from recurrent episodes or post-antibiotic disruption — the Culturelle Pro Strength Daily Probiotics with Prebiotics offers a two-month supply and includes prebiotic support to help beneficial bacteria establish themselves more effectively. Both are gluten and soy free, which matters for many of my clients with additional sensitivities.

For those dealing with IBS-related diarrhoea rather than an acute infection, the picture is somewhat different. Recurrent loose stools in IBS-D require a more targeted approach, and I have found the IBS Anti Diarrhea Probiotic for Diarrhea Relief and IBS-D to be a clinically studied option worth discussing with your healthcare provider. It is specifically formulated for long-term comfort in IBS-D rather than acute illness.

Soluble Fibre to Normalise Stool Consistency

Once you are past the acute phase, soluble fibre can play a genuinely useful role in restoring normal bowel function. Soluble fibre absorbs water in the gut, forming a gel-like consistency that helps bulk and slow transit — the opposite of what diarrhoea does. Psyllium husk is one of the most well-researched soluble fibres for this purpose and is gentle enough to introduce during the recovery phase.

The NOW Foods Psyllium Husk Caps 500mg are a reliable, non-GMO verified option that I frequently recommend for clients rebuilding after a digestive episode. Those who prefer a higher-dose option may find the Premium Psyllium Husk Fibre Supplement at 1450mg more suitable. Always introduce psyllium gradually and with plenty of fluid — and wait until the acute diarrhoea has resolved before starting, as adding fibre too early can irritate an already inflamed gut.

My Nutritionist Recommendation: A Practical Rehydration and Recovery Plan

When it comes to electrolytes, diarrhoea, and rehydration, the evidence is clear and the practical steps are straightforward. The challenge is simply knowing what to do and having the right things to hand when you need them. Here is the approach I recommend to clients, and the one I would follow myself.

During active diarrhoea, stop relying on plain water as your sole source of hydration. Begin using an electrolyte solution — a product like NormaLyte Pure, or the Basic Care Electrolyte Packets — alongside water, sipped steadily throughout the day rather than consumed in large amounts at once. Small, frequent sips are absorbed far more effectively than large gulps, which can trigger further gut spasms. Aim for roughly 200 to 400ml of electrolyte solution per loose stool episode as a general guide for adults, adjusting for your own tolerance.

As symptoms ease, begin introducing easily digestible foods — plain rice, boiled potato, banana, and toast are time-honoured for good reason. Within two to three days of symptom improvement, introduce a quality probiotic and consider adding psyllium husk once bowel movements are becoming more formed.

Most importantly, take this seriously from the start. Dehydration during diarrhoea is not a minor inconvenience — it can become a medical emergency more quickly than most people realise, particularly for children and older adults. Building a small digestive health kit at home, with electrolyte sachets and a probiotic supplement, costs very little and could make a significant difference when you need it most.

If your symptoms are severe, bloody, or persist beyond seventy-two hours without improvement, please see your doctor. No supplement or nutrition strategy replaces appropriate medical assessment when it is warranted.

Have questions about your own digestive health or recovery from a stomach bug? Leave a comment below or get in touch — I am always happy to help you navigate the details and find an approach that works for you.