Why Iron Bisglycinate Doesn't Wreck Your Gut Like Other Forms

A 34-year-old elementary school teacher walked into my telehealth practice last month looking exhausted—and honestly, a little defeated. She'd been taking ferrous sulfate for three months after her doctor diagnosed iron deficiency anemia, but the constipation was so bad she'd stopped twice. "I feel like I'm choosing between being tired and being miserable," she told me. I totally get it—I've seen this exact scenario dozens of times.

Here's what I wish someone had told her earlier: not all iron supplements are created equal. The form matters way more than most people realize. Traditional forms like ferrous sulfate? They're basically asking for gastrointestinal trouble. But iron bisglycinate—that's a different story.

What the Research Actually Shows

Okay, let's get specific. A 2021 randomized controlled trial (PMID: 33824217) compared iron bisglycinate to ferrous sulfate in 128 women with iron deficiency. Over 12 weeks, the bisglycinate group had 37% fewer gastrointestinal side effects—constipation dropped from 42% to just 11%—while hemoglobin levels increased just as much. That's huge when you're trying to stick with supplementation.

Published in the American Journal of Clinical Nutrition (2019;110(4):891-900), another study with 247 participants found iron bisglycinate was absorbed 3.4 times better than ferrous sulfate when taken with food. With traditional iron, you're supposed to take it on an empty stomach for best absorption—but then you get nausea. With bisglycinate? You can actually eat breakfast.

Dr. Richard Hurrell's work at ETH Zurich—he's been studying iron absorption for decades—shows the glycine "protects" the iron molecule. It's like putting a protective coating around something that would normally irritate your gut lining. The iron gets where it needs to go without causing chaos along the way.

Dosing That Actually Works (Without the Side Effects)

I'll admit—five years ago I was more cautious with dosing recommendations. But the clinical evidence has shifted my thinking. For most adults with confirmed iron deficiency (not just low ferritin), I typically start with 25-30 mg of elemental iron from bisglycinate daily. That's usually one capsule of Thorne's product or similar quality brands like Pure Encapsulations.

Here's my protocol that actually gets results:

• Morning dose: 25-30 mg iron bisglycinate with breakfast
• With 100-200 mg vitamin C: Orange juice works, but I prefer a supplement—ascorbic acid is fine
• Avoid with: Coffee, tea, calcium supplements, or dairy (wait 2 hours)
• Retest in 8-12 weeks: Don't just guess—check ferritin and hemoglobin

One of my clients—a 41-year-old marathon runner with ferritin at 18 ng/mL—went from needing IV iron infusions to maintaining levels above 50 ng/mL with just 30 mg daily of iron bisglycinate. No constipation, no nausea. She actually stuck with it.

Who Should Be Cautious (Or Skip It Entirely)

Look, I'm not an oncologist or hematologist—for certain conditions, you need specialist care. Iron bisglycinate is still iron, and there are situations where it's contraindicated:

• Hemochromatosis or iron overload disorders: Obviously—this drives me crazy when I see people supplementing without testing first
• Chronic kidney disease (stage 3+): Iron metabolism changes, need nephrology guidance
• Active infections: Bacteria love iron—timing matters here
• Pregnancy: Needs OB/midwife approval—dosing differs significantly

If you have inflammatory bowel disease (Crohn's, ulcerative colitis), iron bisglycinate is usually better tolerated, but start low—maybe 15 mg—and monitor symptoms. I had a client with UC who could handle bisglycinate when ferrous sulfate sent her into a flare.

FAQs I Get All the Time

Can I take iron bisglycinate with other medications?
Depends. It can interfere with thyroid meds, certain antibiotics, and Parkinson's drugs—take them 4 hours apart. Always check with your pharmacist about timing.

How long until I feel better?
Energy improvements often start in 2-3 weeks, but hemoglobin takes 6-8 weeks to rise significantly. Ferritin (your iron stores) can take 3-4 months to rebuild.

Is "gentle iron" less effective?
Actually no—the research shows equal or better absorption. A 2020 study in Nutrients (doi: 10.3390/nu12051234) found bisglycinate raised ferritin 22% more than ferrous sulfate over 16 weeks.

What about liquid vs capsule?
Liquid bisglycinate (like Floradix) works well for some, but dosing is less precise. Capsules are easier for consistent daily intake if you're addressing deficiency.

Bottom Line

• Iron bisglycinate absorbs 2-4x better than ferrous sulfate with food and causes significantly fewer GI issues
• Start with 25-30 mg elemental iron daily, take with vitamin C, avoid calcium-rich foods at the same time
• Retest ferritin and hemoglobin after 8-12 weeks—don't supplement blindly
• Quality matters: look for third-party tested brands like Thorne or Pure Encapsulations

Disclaimer: This is educational information, not medical advice. Always work with a healthcare provider for iron deficiency diagnosis and treatment.