Malabsorption and food intolerance (SACE Stage 2 Nutrition)
“Explain the causes and consequences of malabsorption syndromes and food intolerances, including lactose intolerance and coeliac disease”
Malabsorption means the digestive system cannot break down or absorb one or more nutrients properly, often because an enzyme is missing or the gut lining is damaged. Lactose intolerance happens when there is too little of the enzyme lactase, so milk sugar passes undigested into the large intestine and causes bloating and diarrhoea. Coeliac disease is an immune reaction to gluten that damages the small intestine and reduces absorption of many nutrients. You should be able to explain the causes, consequences and dietary management of these conditions.
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What this dot point is asking
You need to explain what malabsorption is, give the causes and effects of lactose intolerance and coeliac disease, and describe how each is managed through diet.
What malabsorption is
Malabsorption is the failure to digest or absorb nutrients normally. It can affect a single nutrient or many at once. Common causes include a missing or low enzyme, damage to the intestinal lining (which reduces the surface area for absorption), or problems with bile or pancreatic secretions.
Because the small intestine relies on a huge surface area of villi and microvilli to absorb nutrients, anything that damages or flattens this lining can cut absorption sharply. The consequences are often nutrient deficiencies, weight loss, fatigue and digestive symptoms such as bloating and diarrhoea.
A food intolerance is a non-immune difficulty handling a food, usually because an enzyme is missing. It is different from a food allergy, which is an immune system reaction that can be severe. Coeliac disease is unusual because it involves the immune system but is not a classic allergy.
Lactose intolerance
Lactose is the sugar in milk. It is digested by the enzyme lactase, which splits it into glucose and galactose for absorption. In lactose intolerance, the body makes too little lactase.
Undigested lactose passes into the large intestine, where bacteria ferment it. This draws water into the bowel and produces gas, causing bloating, cramps, wind and diarrhoea after dairy foods. It is uncomfortable but not dangerous.
Management is dietary: limiting lactose, choosing lactose-free or low-lactose products, or using lactase supplements. Many people tolerate small amounts and hard cheeses or yoghurt, which contain less lactose. Care is needed to maintain calcium intake from suitable alternatives.
Coeliac disease
Coeliac disease is an autoimmune condition triggered by gluten, a protein in wheat, rye and barley. In a person with coeliac disease, eating gluten causes the immune system to attack the lining of the small intestine, flattening the villi.
With the villi damaged, the absorptive surface shrinks, leading to malabsorption of many nutrients: iron, calcium, folate and fat-soluble vitamins among them. Symptoms can include diarrhoea, weight loss, fatigue, anaemia and, in children, poor growth.
Management is a strict, lifelong gluten-free diet. When gluten is removed, the gut lining heals and absorption recovers. This requires careful label reading and awareness of hidden gluten, which links to the food labelling content in Topic 2.
Lactose intolerance is an enzyme problem: too little lactase to digest milk sugar. Coeliac disease is an autoimmune reaction to gluten that damages the small intestine. One is uncomfortable; the other causes real damage and widespread malabsorption if gluten continues.
Why this matters
Malabsorption shows why digestion and absorption matter, not just intake. A person can eat plenty of a nutrient yet still become deficient if it cannot be absorbed. These conditions also demonstrate the difference between intolerance, allergy and autoimmune disease, a distinction examiners often test.
Step 1: Identify the missing enzyme
In lactose intolerance the small intestine makes too little lactase, the enzyme that splits the milk sugar lactose into glucose and galactose. Without enough lactase, lactose stays whole.
Step 2: Follow the undigested lactose
Because it is not broken down, the lactose is not absorbed in the small intestine and passes on into the large intestine still intact.
Step 3: Bacteria ferment it
Gut bacteria ferment the lactose, producing gas and drawing water into the bowel by osmosis. This is the direct cause of the symptoms, not the lactose itself.
Step 4: Link to the symptoms and management
The gas and extra water cause bloating, cramps, wind and diarrhoea after dairy. Management is dietary: limit lactose, use lactose-free products or lactase supplements, and keep calcium intake up. Naming lactase, the fermentation, and the osmotic effect is what earns the marks.
- Calling coeliac disease an allergy
- It is an autoimmune condition, not a classic allergy. Gluten triggers an immune attack on the gut lining.
- Saying lactose intolerance is dangerous
- It causes discomfort, not harm, and many people tolerate small amounts. A gluten reaction in coeliac disease, by contrast, damages the gut.
- Confusing cause with symptom
- Bloating and diarrhoea are symptoms; the cause of lactose intolerance is low lactase, and the cause of coeliac symptoms is villi damage from gluten.
- Forgetting the nutrient gaps
- Removing dairy or gluten foods can lower calcium, iron or fibre intake, so the replacement diet must be planned.
In short, malabsorption is the failure to digest or absorb nutrients, with lactose intolerance caused by low lactase and coeliac disease caused by an autoimmune reaction to gluten, each managed by careful dietary change.
Exam-style questions
Questions in the style of SACE Board exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
2019 SACE Stage 2-style2 marksExplain why a person who has coeliac disease is at risk of developing nutrient deficiencies.Show worked answer →
For 2 marks, link the cause (damage to the gut) to the effect (poor absorption).
In coeliac disease, eating gluten triggers an immune reaction that damages and flattens the villi lining the small intestine (1 mark). The villi are the finger-like projections that provide the large surface area needed for nutrient absorption.
With the villi damaged, the surface area for absorption is greatly reduced, so nutrients pass through without being properly absorbed. This malabsorption leads to deficiencies in nutrients such as iron, calcium and some vitamins (1 mark).
2019 SACE Stage 2-style2 marksState one nutrient deficiency and the subsequent diet-related disorder that could develop in a person who has coeliac disease.Show worked answer →
One mark for naming a nutrient deficiency, one mark for the matching disorder.
A good pairing is iron deficiency, which can lead to iron-deficiency anaemia. Because the damaged small intestine cannot absorb iron properly, red blood cells cannot carry enough oxygen, causing tiredness and weakness.
An equally acceptable pairing is calcium and vitamin D deficiency leading to osteoporosis (weak, brittle bones), since poor calcium absorption reduces bone density over time.
Practise this
Sources & how we know this
- Stage 2 Nutrition subject outline (2025 onwards) — SACE Board
- Stage 2 Nutrition: external assessment — SACE Board