How high sugar intake dehydrates your body and slows gut movement

Sugary drinks and processed foods don't just spike blood sugar, they also cause dehydration and slow digestion. Experts share what happens in the gut and how to reverse it

Excess sugar is often linked to weight gain and diabetes, but doctors say its effects on digestion are just as important, and far less understood. From drawing water out of the colon to slowing gut contractions, too much sugar can quietly set the stage for constipation, dehydration and sluggish digestion. Here’s what experts say is really happening inside the body.

 

Why too much sugar slows the gut

 

Dr Ashish Gautam, principal director, robotic and laparoscopic surgery at Max Super Speciality Hospital, explains that eating large amounts of free sugars often pushes out fibre-rich foods. “Instead of fruits, vegetables, and whole grains that help the gut move, people eat processed foods and sugary drinks,” he says.

 

With less fibre to bulk up stool, the colon has to work harder. On top of that, excess sugar disrupts the gut’s osmotic balance and alters bacterial activity, weakening the coordinated contractions that move stool forward. Dr Amit Sakaria, general physician, Ruby Hall Clinic Pune, adds that unabsorbed sugars, especially fructose, can pull water into the small intestine, upsetting the environment needed for smooth digestion.

 

How sugar causes dehydration and harder stools

 

Both doctors point to sugar’s osmotic effect. Free sugars attract water into the gut, initially causing bloating, but leaving the colon short of the moisture needed to soften stool.

 

Dr Gautam notes that high blood glucose also triggers frequent urination, “High sugar intake boosts blood sugar levels, which makes you urinate more and lose even more water from your body.”

 

Dr Sakaria calls this a “double dehydrating effect", where water is held in the gut and simultaneously lost through urine, drying out stool even further.

 

Why sugary drinks are worse than sugary foods

 

• Deliver large amounts of sugar quickly
• Cause sharper blood sugar spikes and more urination
• Contain zero fibre
• Suppress appetite for balanced meals
• Often exceed WHO’s daily sugar limits in a single serving

 

Dr Gautam warns that a single soft drink or packaged juice can cross the 25-gram daily free sugar limit. Sugary beverages also lack chewing stimulation which is an important trigger for activating digestion.

 

Who is most at risk?

 

Children: higher sugar exposure and lower fibre intake, poor fructose absorption

 

Older adults: slower gut motility, reduced thirst, medications that worsen constipation

 

People with diabetes: higher urinary fluid loss and greater dehydration risk

 

Individuals with IBS or fructose malabsorption: difficulty processing sugars

 

How fast does the gut recover after cutting sugar?

 

Most people notice relief within 2–3 days of reducing sugar and increasing water and fibre intake.

 

Dr Gautam says many report softer stools and easier passage within one week, while Dr Sakaria notes that full regularity may take one to two weeks, depending on gut health.

 

Simple ways to prevent sugar-induced constipation

 

• Keep free sugar below 25 grams/day (WHO guideline)
• Avoid sugar-sweetened beverages
• Drink enough water through the day
• Prioritise fibre from fruits, vegetables, whole grains
• Choose whole fruits over fruit juices
• Add fermented foods and prebiotic fibre to support gut microbes
• Maintain regular meal timings

 

Both experts say the solution isn’t complicated - limit sugar, boost hydration, and bring fibre back to the centre of the plate. They emphasise that the gut can reset surprisingly quickly once these basics fall into place.   

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This report is for informational purposes only and is not a substitute for professional medical advice.