Normal nutritional requirements across childhood: Case

This girl presents the picture of an adolescent whose dietary change has left her short of several requirements at once. Her fatigue, pallor, microcytic anaemia with a haemoglobin of 92 grams per litre, and ferritin of 6 micrograms per litre establish iron deficiency anaemia. Her weight falling from the 40th to the 15th centile while her height holds on the 50th shows that her energy and protein intake are also failing to meet her requirements. The strict vegan diet begun nine months ago, combined with the onset of menstruation, explains both gaps. [7]

Clinical findings

The clinical picture is one of nutritional inadequacy in an adolescent at a high-requirement life stage. The weight falling from the 40th to the 15th centile over a year is downward centile crossing, the single most reliable sign of failing to meet requirements. Her height remaining on the 50th centile shows that the deficit is recent enough to have affected weight before length, consistent with the timeline of her dietary change. [1]

The iron deficiency is driven by two converging factors. Her vegan diet removes the most bioavailable source of iron, which is haem iron from meat, and her recently commenced menstruation adds an ongoing iron loss. The recommended dietary allowance for iron in adolescent females is 15 milligrams per day, the highest of any age group in childhood, precisely because menstruation compounds the baseline requirement. Her diet is providing far less than this. [7]

Her body mass index on the 12th centile confirms that her energy intake is below her requirement. Adolescence is a period of increased energy and protein need because of the pubertal growth spurt, and a poorly planned vegan diet that is low in energy-dense foods can fall short. The candidate must assess the whole requirement, not only the iron that the blood test revealed. [2]

Investigations and diagnosis

The diagnosis of iron deficiency anaemia is already established by the microcytic anaemia and low ferritin. The mean cell volume of 72 femtolitres confirms microcytosis, and a ferritin of 6 micrograms per litre is well below the threshold of 15 micrograms per litre that defines iron deficiency. No further iron workup is needed before starting treatment in a girl with such clear-cut deficiency and an explanatory dietary history. [7]

A broader nutritional assessment is warranted because a vegan diet places several nutrients at risk beyond iron. A 25-hydroxyvitamin D level should be checked, and the candidate should consider vitamin B12, which is absent from an unsupplemented vegan diet and whose deficiency causes megaloblastic anaemia and neuropathy. Calcium and zinc status should be assessed through the diet history, as these are also at risk on a vegan diet. [6]

The growth trajectory should be plotted in full and reviewed. The candidate should confirm that the centile crossing is a real departure from her previous trajectory and not an artefact of a single measurement, and should take a careful diet history to quantify her intake against the requirement for her age. [1]

Management and outcome

Management combines correction of the iron deficiency with a restructured diet that meets her full requirement. Oral elemental iron at about 3 to 6 milligrams per kilogram per day is given until the haemoglobin normalises and for a further two to three months to replete stores. Because her diet is the cause, dietary change must accompany the supplement or the deficiency will recur. [7]

The dietary plan must ensure that her vegan diet meets the adolescent requirement for energy, protein, iron, calcium, zinc, vitamin D and vitamin B12. Iron-rich plant foods such as legumes, fortified cereals and leafy vegetables should be paired with a vitamin C source to enhance absorption, and a daily vitamin B12 supplement is essential. Calcium-fortified plant alternatives and adequate vitamin D are needed to support the peak bone mass she is accruing in these years. [11]

The candidate should counsel her and her family that a vegan diet can meet the requirement at every age, but only with planning and supplementation. The growth faltering and anaemia here are the consequence of an unplanned transition, not of the diet itself. With the iron deficiency corrected, the diet restructured, and growth monitored at regular intervals, her outlook is excellent, and the key teaching point is that any diet, however well intentioned, must be judged against whether it meets the age-specific requirement. [6]