Iron Absorption in a Vegetarian Adolescent
Mia is a 16-year-old who has followed a lacto-ovo vegetarian diet for two years. Her recent fasting blood test shows ferritin 11 µg/L (reference 15–150), haemoglobin 118 g/L (reference 120–160), and MCV at the low end of normal. She reports fatigue during netball training and frequent headaches. A 24-hour recall shows: breakfast of two slices wholemeal toast with peanut butter and a glass of orange juice; lunch of a lentil and spinach salad with wholemeal pita; afternoon tea of a black tea and two digestive biscuits; dinner of chickpea curry with brown rice; and a calcium-fortified soy milk before bed. She drinks black tea with most meals and takes a calcium supplement at breakfast on her doctor's advice. Her GP has asked you to review her diet before considering an iron supplement.
1. Identify the factors in Mia's current intake that are most likely reducing her non-haem iron absorption, and explain the physiological reasoning for each.
Read the worked answer
Non-haem iron from plant foods is poorly absorbed and is strongly influenced by meal composition. In Mia's diet, three factors stand out.
1. Tea with meals. Black tea contains polyphenols (tannins) that bind non-haem iron in the gut lumen, forming complexes that cannot be taken up by enterocytes. Drinking tea with most meals could reduce absorption of that meal's iron by a substantial margin. Moving tea to between meals (at least an hour away from iron-containing meals) is a simple, high-impact change.
2. Calcium at breakfast. Calcium is the only known inhibitor of both haem and non-haem iron absorption, and it acts within a single meal rather than on overall daily intake. Her calcium supplement at breakfast, alongside the fortified soy milk at night, means calcium is present at the meal where peanut butter and wholemeal toast provide her main plant iron. Moving the supplement to a meal with low iron content (or to bedtime, away from the soy milk) reduces this competition.
3. Phytates in wholemeal and legumes. Wholemeal bread, brown rice, lentils and chickpeas are high in phytate, which chelates iron. This is not a reason to remove these foods - they are her main iron sources - but it explains why her intake may look adequate on paper while absorption is low.
The protective factor already present is the orange juice at breakfast: vitamin C and other organic acids reduce ferric iron to the more absorbable ferrous form and form soluble chelates with iron, partially counteracting phytate. Strengthening this pairing at every main meal is the practical lever.
2. Mia asks whether she should simply take an iron supplement rather than change her diet. Using the blood results and dietary information, justify a recommendation and outline the dietary changes you would prioritise.
Read the worked answer
Her results are consistent with early iron deficiency: ferritin is below the reference range, haemoglobin is mildly reduced, and MCV is at the low end, indicating iron stores are depleted before frank anaemia develops. Symptoms of fatigue and headaches fit this picture but are non-specific, so they cannot be used alone to confirm the diagnosis.
A supplement is not automatically the first step, and it is not a decision for a nutritionist to make unilaterally. High-dose oral iron causes gastrointestinal side effects (constipation, nausea, dark stools) that reduce adherence, and it should be prescribed and monitored by her GP, with a repeat blood test to confirm response. The more defensible recommendation is to correct the dietary inhibitors first, because the problems identified are modifiable and because dietary change is sustainable long term.
Priorities:
- Separate tea from meals. Move black tea to at least one hour after eating, or replace it with water or a vitamin C-rich drink at meals.
- Pair vitamin C with every iron-containing meal. Orange juice or citrus at breakfast; tomato, capsicum or lemon with the lentil salad and chickpea curry.
- Relocate the calcium supplement to a low-iron time, and avoid taking it with the iron-rich breakfast.
- Add a vitamin C source to the legume meals and consider soaking or sprouting legumes to reduce phytate.
- Include a modest source of vitamin C-rich fruit as snacks rather than biscuits.
If ferritin does not improve on a repeat test after these changes, a supplement becomes clearly indicated and should be managed medically. The key judgement is that diet change is the appropriate first-line response here, with supplementation as a monitored escalation rather than a substitute for addressing the causes.