Why Fasting Causes Diarrhea for Some People (and How to Fix It)

Many people try water or extended fasting and are surprised to find themselves running to the bathroom — not because of hunger, but due to unexpected loose stools or full-blown diarrhea.

It’s a frustrating (and sometimes alarming) experience, but not uncommon. This post dives into the real reasons why fasting can cause digestive upset, what’s happening in your body, and how to prevent or correct the issue so you can fast safely and effectively.

Common Symptoms Reported During Fasting:

Watery or loose stools
Sudden urgency or multiple bowel movements
Cramping or gurgling intestines
Diarrhea after drinking lemon water, electrolytes, or black coffee

If this sounds familiar, you’re not alone — and the good news is, it’s often fixable with a few smart changes.

1. What Causes Diarrhea During Fasting?

Let’s break down the main factors:

1.1. Electrolytes Can Act as Laxatives

Many fasters use electrolyte blends or ORS (oral rehydration salts) — but these often contain high doses of magnesium or sodium, which can loosen the bowels.

Magnesium citrate, for example, is commonly used as a laxative. Even **too much sea salt in lemon water** can pull water into the intestines via osmosis, creating a flushing effect.

1.2. Caffeine Accelerates Gut Motility

Black coffee and green tea are popular fasting staples — but both contain **caffeine**, a known gastrointestinal stimulant. It increases peristalsis (the movement of the bowels), especially on an empty stomach.

If you’re combining coffee, tea, and lemon water with electrolytes, you may unintentionally be stacking multiple gut stimulants.

1.3. Bile Dumping

During fasting, your liver continues producing bile even though there’s no fat to digest. This excess bile can sometimes dump into the intestines and irritate the colon, especially in people who are bile-sensitive or lack a gallbladder.

1.4. Gut Microbiome Shifts

Fasting changes your gut environment. As bad bacteria die off, it can trigger a mild “detox” response — including diarrhea, bloating, or irregularity. This usually settles within a few days of adjustment.

1.5. Hidden Magnesium in Supplements

Check your electrolyte labels: some contain magnesium oxide or citrate, both known for their laxative effects. Even some “clean” electrolyte brands have enough magnesium to trigger urgency in sensitive individuals.

2. What’s the Difference Between Detox and Digestive Distress?

Not all diarrhea during fasting is dangerous. In some cases, it may be part of the body clearing out waste, especially during the first 24–48 hours.

But how do you know when to stop or modify your fast?

Signs It May Be Detox or Temporary:

Lasts less than 24 hours
No major cramping or dehydration
No blood or mucus in stool
Coincides with electrolyte intake or increased caffeine

Signs It May Be Harmful or Need Adjustment:

Lasts more than 2 days or worsens with time
Causes dizziness, weakness, or dehydration
Accompanied by fever, pain, or nausea
Happens every time you attempt a fast

If your fasting-related diarrhea is repeatable and disruptive, it likely means your current protocol needs to be adjusted.

3. How to Prevent or Manage Diarrhea During Fasting

3.1. Use Electrolytes Cautiously

Stick to products that avoid high doses of magnesium (especially citrate or oxide). Sodium and potassium are typically safer choices during fasting.

3.2. Limit Coffee and Tea to 1–2 Cups

Especially on an empty stomach, caffeine can trigger bowel activity. Try reducing your intake or switching to decaf or herbal alternatives for a few days to observe changes.

Organic decaf coffee
Unsweetened fasting-safe herbal teas

3.3. Watch Your Lemon-Salt Water Mix

While popular, lemon water with salt may overstimulate the gut. Try reducing the lemon to just a few drops, and use no more than 1/4 tsp of sea salt per 500ml of water.

3.4. Add Binding Support if Needed

If loose stools persist, consider gentle binding support to help calm the gut:

Activated charcoal (take away from food/supplements)
Psyllium husk capsules
Slippery elm powder or capsules

4. Should You Break the Fast If Diarrhea Starts?

If you’re dehydrated, dizzy, or feeling weak, yes — break the fast gently.

Start with a small bowl of bone broth, a piece of avocado, or soft steamed veggies to slow the gut down and restore balance.

Bone broth powder (gentle refeed)

5. Can You Fast Again After This Happens?

Absolutely — but modify your approach.

Next time, try:

Fasting for 16–20 hours instead of 48+
Skipping lemon water or caffeine entirely
Using minimal electrolytes or trying lower doses
Switching to a gentler fasting method like 14:10 or alternate-day fasting

Final Thoughts

Diarrhea during fasting can be disruptive, but in most cases, it’s not dangerous — just a sign that something in your routine needs adjusting.

Whether it’s too much magnesium, stacked stimulants, or bile sensitivity, the solution is usually found through simplifying your inputs, using fasting-safe hydration strategies, and gradually building tolerance.

Fasting is a powerful tool — but it’s not one-size-fits-all. Listen to your body and adapt as needed to ensure a safe, supportive experience.

Share this post with someone who has struggled with fasting side effects.
And tag @TheResetRitual if you’re sharing your experience or questions.

Disclaimer: This article is for informational purposes only and is not medical advice. Always consult your healthcare provider before starting a fasting regimen or supplement routine. This post may contain affiliate links. As an Amazon Associate, I earn from qualifying purchases.

Why Fasting Causes Diarrhea for Some People (and How to Fix It) | The Reset Ritual