Still Iron Deficient After Years of Supplements? Here’s What You Need to Know About Gut Health and Iron Absorption

Written by Karly Raven, BHSc - Naturopath and SIBO Specialist, Nourished Gut Clinic
Last updated: August 2026

Have you been taking iron supplements for months, or even years, only to find that your levels have not improved? You are not alone. Persistent iron deficiency is a common struggle, even for people who eat iron-rich foods and follow their doctor's advice on supplementation. The missing piece is often gut health.

At a glance

Low iron is one of the most commonly missed consequences of untreated gut dysfunction. If you are supplementing but your levels are not improving, your gut rather than your diet may be the problem.

In this post you will learn why SIBO and intestinal permeability interfere with iron absorption, the signs your gut is blocking iron uptake, and what a naturopathic approach to restoring both looks like.

Jump to a section

1. Understanding iron deficiency and its symptoms
2. The role of gut health in iron absorption
3. Why iron supplements might not be enough
4. A whole-system approach to resolving iron deficiency
5. Frequently asked questions

1. Understanding iron deficiency and its symptoms

Iron deficiency is one of the most widespread nutritional deficiencies worldwide. It occurs when your body does not have enough iron to produce haemoglobin, the protein that enables red blood cells to carry oxygen. Without sufficient iron, your body struggles to function well, and the symptoms show up across your whole day.

Common symptoms of iron deficiency include:

• Chronic fatigue. Feeling tired all the time, even after a good night's sleep.
• Weakness and dizziness. Lightheadedness, especially when standing up quickly.
• Shortness of breath. Difficulty breathing during everyday activities or exercise.
• Pale skin and brittle nails. Physical signs that reflect low oxygen carrying capacity.
• Frequent infections. Iron is essential for immune function, and low levels leave you more susceptible.

If you are experiencing these, it is worth getting a full iron panel rather than ferritin alone. But before you reach for another supplement, it is worth understanding why your gut may be the reason it is not working.

2. The role of gut health in iron absorption

Iron absorption takes place in the small intestine, specifically the duodenum and upper jejunum. That is precisely where SIBO happens. If your small intestine is not functioning properly, it can significantly reduce your ability to absorb iron, no matter how many supplements you take or how much red meat you eat.

Here is how gut health affects iron absorption:

• Inflammation. Inflammatory Bowel Disease, coeliac disease or chronic low grade inflammation can compromise the gut lining, reducing its capacity to absorb nutrients including iron.
• Bacterial overgrowth. SIBO is an overgrowth in the exact stretch of bowel where iron is absorbed. Alongside bloating and gas, nutrient deficiencies are one of its most common consequences, and iron is usually the first to show.
• Low stomach acid. Adequate stomach acid is needed to convert dietary iron into a form your body can absorb. Low stomach acid, whether from chronic stress, age, or acid-reducing medication, meaningfully reduces uptake.
• Microbiome imbalance. An imbalanced microbiome, often following antibiotics, a low fibre diet or prolonged restriction, impairs how well your body absorbs nutrients generally.

If you want to understand what is happening in that part of the bowel, the three types of SIBO explains the mechanism and why subtype matters.

3. Why iron supplements might not be enough

Iron supplements are the standard recommendation, and they are not wrong. They are just frequently insufficient when there is an absorption problem underneath.

• Poor absorption. If the small intestine is inflamed or overgrown, your body will not absorb much of what you take, which is why levels stay stubbornly low despite consistent supplementation.
• Side effects that make things worse. Iron commonly causes constipation, nausea and cramping. In someone with an existing gut condition, that can worsen the symptom picture and reduce compliance.
• Iron feeds some of the organisms you are trying to reduce. Unabsorbed iron in the gut can support the growth of organisms such as E. coli, which is one of the main hydrogen producers in SIBO. This is a genuine clinical consideration when someone has both low iron and an active overgrowth, and it is one reason sequencing matters.
• It does not address the reason. Supplements can lift levels temporarily, but if absorption is the problem, levels fall again once you stop.

This is why I assess the gut before committing someone to long-term iron supplementation, rather than after a year of it has not worked.

4. A whole-system approach to resolving iron deficiency

To resolve iron deficiency properly, you need to address both the iron and the absorption.

• Test comprehensively. A full iron panel including ferritin, serum iron, transferrin saturation and TIBC, alongside inflammatory markers. Ferritin alone can be misleading, because it rises with inflammation and can look reassuring when iron stores are genuinely low.
• Optimise the diet. Iron-rich foods paired with vitamin C to enhance absorption. Be aware that tea, coffee and calcium taken alongside iron reduce uptake, so timing matters as much as intake.
• Support digestive capacity. Stomach acid, bile and enzyme function all sit upstream of absorption. Addressing them often does more for iron levels than increasing the dose.
• Treat the overgrowth if there is one. If SIBO is present, treating it is what allows absorption to recover. SIBO treatment covers what a complete protocol involves.
• Choose the right form. Not all iron is equally tolerated. Gentler forms exist and are often better absorbed in people with sensitive digestion. This is worth individualising rather than defaulting to whatever is on the shelf.

Resolving iron deficiency is rarely just about taking more iron. It is about understanding why the iron is not getting in.

Frequently Asked Questions

Why is my ferritin still low after months of iron supplements?

The most common reason is an absorption problem rather than an intake problem. Iron is absorbed in the duodenum and upper jejunum, which is exactly where SIBO occurs, so an overgrowth there directly interferes with uptake. Low stomach acid, inflammation and coeliac disease do the same thing. If you have been supplementing consistently for three months without meaningful change, absorption is worth investigating.

Can SIBO cause iron deficiency?

Yes, and it is one of the more common consequences I see. The overgrowth sits in the part of the small intestine responsible for absorbing iron, and it also drives low grade inflammation which further impairs uptake. Treating the overgrowth is often what finally allows iron levels to rise and stay there.

Should I stop taking iron if I have SIBO?

Not without discussing it with your practitioner, because untreated iron deficiency carries its own risks. It is a sequencing and dosing question rather than a stop or continue one. Unabsorbed iron can support the growth of some organisms involved in SIBO, so the form, dose and timing are worth individualising while the overgrowth is being treated.

What iron tests should I ask for?

A full iron studies panel rather than ferritin in isolation. That means ferritin, serum iron, transferrin saturation and TIBC, ideally alongside an inflammatory marker such as CRP. Ferritin behaves as an acute phase reactant, meaning inflammation pushes it up, so a normal looking ferritin in someone with an inflamed gut can hide genuinely depleted stores.

Ready to get to the root cause?

If you have been supplementing for months without your levels shifting, the answer is not usually a higher dose. It is working out what is blocking absorption.

If you want a practical starting point, the free 3-Day Bloat Fix is a short plan you can begin this week.

The Nourished Gut Program is our six month process for rebuilding digestive function, and it uses comprehensive blood pathology so we can see exactly what your iron is doing alongside everything else. Testing and supplements are arranged separately and are not included in the program fee. It is application only and we take five new clients each month. Book a free Digestive Strategy Session, a 20 minute telehealth call, and we will tell you honestly whether it suits your case.

Karly Raven, BHSc is a naturopath, microbiome restoration specialist, and SIBO expert. She is the founder of the Nourished Gut Clinic and creator of the Feed Forward methodology and the SIBO Restore Diet. Karly works with people with IBS, SIBO, IBD and chronic gut conditions, and mentors health practitioners through karlyraven.com.

This blog is for educational purposes only and does not constitute medical advice. Please consult a qualified health practitioner before making changes to your treatment plan.