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Many supplements that are marketed as “healthy” can actually disrupt gut function if used inappropriately, or in excess, or by people with sensitive gastrointestinal tracts. I always preface with ‘may’ because there are obviously a ton of benefits to taking some of these supplements, such as if you’re pregnant and anemic, then you definitely need iron, but knowing the pitfalls, balancing the risks and benefits, and proactively working on your gut health will help!
Why they’re a problem: Iron is irritating to the gut lining and slows intestinal transit.
Common effects: Constipation, bloating, nausea, cramping, dark (black!) stools.
Particularly risky for: People with pre-existing constipation, IBS, or low gut motility.
But: essential for anemic pregnant people!
Solution: Use lower doses, take with food, or consider chelated forms if medically appropriate, such as iron (ferrous) bisglycinate.
Why they’re a problem: Magnesium oxide is poorly absorbed → draws water into the gut → can cause diarrhea. Magnesium citrate can cause dehydration.
Common effects: Cramping, loose stools, urgency, electrolyte imbalance with chronic use.
Better tolerated: Magnesium glycinate in moderate doses for most people.
However, magnesium oxide is the best form for constipation, precisely because it works so well! I recommend magnesium oxide 400mg daily for constipation. See my Magnesium post here. Magnesium, An Oldie But Goodie – by Carmen Fong, MD
Why they’re a problem: These poorly absorbed sweeteners ferment (create gas) in the colon.
Common effects: Gas, bloating, diarrhea, discomfort, worsened IBS symptoms. Lotsa farts.
Hidden sources: “Sugar-free” fiber gummies, protein powders, prebiotics, or chewable vitamins.
Yes, they make your sweets ‘sugar-free’ and are great for those who are diabetic or otherwise aiming for good glucose control. But I say, try to avoid these if you can!
Why they’re a problem: Not all strains are beneficial for everyone. Some probiotics increase gas or bloating, especially early on or in people with SIBO.
Common effects: Distension, worsening constipation or diarrhea, discomfort.
Tip: Strain specificity matters — e.g., Lactobacillus rhamnosus GG has evidence for antibiotic-associated diarrhea, but random blends may not help and can backfire. See my post on Probiotics here. Which Gut Health Pills Are Best? A Guide to Choosing the Right Supplement
Why they’re a problem: Stimulant laxatives irritate the colon to force peristalsis. Thats how they work. Chronic use can cause dependency and mucosal irritation.
Common effects: Cramping, melanosis coli (dark stains inside the colon, not dangerous, but weird), worsening constipation when stopped.
Short-term use only is usually advised clinically. Most recently, senna has been shown to be safe for long-term use. The others, not so much.
Solution: Use osmotic laxatives like Miralax and fiber supplements like psyllium instead, and save the stimulant laxatives for ‘emergencies’, like once in a while when you haven’t pooped in three days. See my post on Herbal Remedies here.
Why they’re a problem: Prebiotics like inulin and FOS are rapidly fermented (again, broken down by gas-creating bacteria in your gut).
Common effects: Severe bloating, flatulence, pain, loose stools — especially in patients with IBS or small intestinal bacterial overgrowth (SIBO).
Tip: Start with very low doses and titrate slowly (like add 5mg a week) or use gentler soluble fibers– psyllium is the only clinically proven one, though we are seeing results for flaxseed fiber and acacia fiber.
Why they’re a problem: Many contain gums, emulsifiers (e.g., carrageenan, polysorbate-80), and artificial sweeteners, which can disrupt gut barrier function and microbiome balance. Not to mention, more protein is like adding more concrete to your colon.
Common effects: Bloating, loose stools, “IBS-like” flares, constipation.
Solution: Use sparingly and continue to eat a healthy, balanced diet with fruits, vegetables, legumes and grains at every meal.
Why they’re a problem: High doses of fat-soluble vitamins, zinc, or calcium can irritate the GI tract, slow motility, or disrupt microbiota. Too much Vitamin C can cause kidney stones!
Common effects: Nausea, constipation (calcium), metallic taste, altered bowel habits.
Solution: More is not better. While we should be getting our vitamins and minerals, from eating the rainbow, the fact is that most of us do not get what we need. Stick with one reliable, clinician-backed multivitamin.
Bottom Line: This holiday season, eat the rainbow, everything in moderation, and trust your gut!
