Ferrous bisglycinate (iron bisglycinate chelate) is absorbed just as effectively as ferrous sulfate at lower doses, with significantly fewer GI side effects. The evidence supports bisglycinate as the first-line choice for iron supplementation whenever cost permits.
Overview
Iron supplementation is frequently recommended but poorly tolerated — with ferrous sulfate, the most commonly prescribed form, causing significant GI side effects that lead many people to stop taking it. Ferrous bisglycinate (iron glycinate) offers a compelling alternative. Here's the evidence.
What Is Ferrous Bisglycinate?
Iron chelated to two glycine molecules. The chelation protects iron from inhibitory factors in the gut (phytates, tannins, calcium) that reduce standard iron absorption, and allows absorption through a different transporter pathway than ionic iron forms.
Best for: Iron deficiency anaemia treatment, Pregnancy (excellent GI tolerance), People with GI sensitivity, Long-term iron supplementation.
Standard dose: 25–50 mg elemental iron/day (as bisglycinate — lower doses needed than sulfate).
Side effects: Significantly fewer GI side effects than ferrous sulfate. Mild nausea possible but much less common. Stools may darken..
What Is Ferrous Sulfate?
The most widely prescribed iron supplement globally. An inorganic iron salt with well-established efficacy for treating iron deficiency anaemia. Standard of care in many national health systems due to its low cost and established evidence base.
Best for: Iron deficiency anaemia (standard treatment), Cost-sensitive supplementation, Short-term repletion when GI side effects can be managed, Situations where physician prescribes it.
Standard dose: 100–200 mg elemental iron/day in divided doses (much higher than bisglycinate due to lower relative absorption efficiency).
Side effects: Constipation (very common), nausea, dark stools, abdominal cramps, heartburn. Side effects cause ~20–25% of patients to discontinue. Worst on empty stomach..
Evidence & Absorption Scores
We scored both on four dimensions: quality of clinical evidence, bioavailability, GI tolerance, and value for money. Scores are out of 10:
Head-to-Head Comparison
| Category | ▲ Ferrous Bisglycinate | ▲ Ferrous Sulfate |
|---|---|---|
| GI Tolerability | Excellent — significantly fewer side effects | Poor — constipation and nausea in 20–50% of users |
| Bioavailability | High — chelation improves absorption efficiency | Good — but affected by food, phytates, calcium |
| Required Dose | Lower — 25–50 mg elemental iron/day | Higher — 100–200 mg elemental/day often needed |
| Haemoglobin Recovery | Equivalent in RCTs (with lower dose) | Well established over decades |
| Pregnancy Use | Excellent — preferred for GI tolerance | Widely used but poorly tolerated |
| Cost | Higher per unit | Very cheap — widely available generically |
| Interaction with Food | Minimally affected — can take with food | Significantly reduced by food, but less GI upset with food |
| NHS/Prescription Availability | Less commonly prescribed (cost) | Standard NHS and prescription form |
Best Uses for Each
✅ Ferrous Bisglycinate — Best For
- Iron deficiency anaemia treatment
- Pregnancy (excellent GI tolerance)
- People with GI sensitivity
- Long-term iron supplementation
✅ Ferrous Sulfate — Best For
- Iron deficiency anaemia (standard treatment)
- Cost-sensitive supplementation
- Short-term repletion when GI side effects can be managed
- Situations where physician prescribes it
Who Should Choose Ferrous Bisglycinate?
▲ Choose Ferrous if:
Pregnant women, people with GI sensitivity, athletes, or anyone who has tried ferrous sulfate and experienced unacceptable constipation or nausea. Also the better choice for long-term iron supplementation.
▲ Choose Ferrous if:
Cost-sensitive situations, short-term deficiency correction where GI side effects can be managed, or where bisglycinate is not available. If prescribed ferrous sulfate by a doctor, take it with a small amount of food to reduce (though not eliminate) GI side effects, even though this slightly reduces absorption.
Can You Take Both?
No — combining iron forms provides no benefit and risks iron excess. Iron supplementation should always be guided by blood ferritin testing.
Frequently Asked Questions
The Bottom Line
Ferrous bisglycinate (iron bisglycinate chelate) is absorbed just as effectively as ferrous sulfate at lower doses, with significantly fewer GI side effects. The evidence supports bisglycinate as the first-line choice for iron supplementation whenever cost permits.