Carbohydrate intolerance (lactose, fructose, FODMAP)

Lactose, fructose, and FODMAP intolerance: the AU general practice guide

By Dr HB Lo, FACRRM 8 min read

Lactose intolerance, fructose malabsorption, and FODMAP sensitivity are common causes of bloating, gas, cramping, and altered bowel habit. They are not allergies and do not cause serious bowel disease.

Before treating carbohydrate intolerance, coeliac disease must be excluded — it is a common secondary cause of lactase deficiency, and treating without screening misses the diagnosis. Once coeliac is excluded, a dietitian-led three-phase low-FODMAP program (elimination, structured reintroduction, then personalisation) is the standard approach. A lifelong elimination diet without reintroduction harms gut microbiome diversity and risks nutritional deficiency.

Bloating, abdominal cramping, flatulence, and altered bowel habit after meals are among the most common reasons Australians consult their GP. A significant proportion of these presentations relate to incomplete absorption of fermentable short-chain carbohydrates — a group collectively called FODMAPs, which includes lactose in dairy, fructans in wheat and onions, and fructose in excess of glucose in certain fruits and sweeteners.

These are not allergic or inflammatory conditions. They do not cause damage to the gut lining, do not produce blood in the stool, do not cause weight loss, and carry no risk of serious bowel disease. Understanding this helps both clinician and patient avoid unnecessary investigation and inappropriate long-term dietary restriction.

The critical caveat is that the same symptoms — bloating, loose stool, cramping — are also the presentation of coeliac disease, which damages the small bowel lining and absolutely must not be missed. Coeliac screening is non-negotiable before labelling a patient with carbohydrate intolerance.

A. Core clinical — the AU general-practice framework

The FODMAP framework

The Monash University FODMAP program, developed in Melbourne and the world’s standard resource on this topic, defines FODMAP as: Fermentable Oligo-, Di-, Mono-saccharides And Polyols. The major subtypes relevant to general practice are:

  • Lactose — the disaccharide in dairy products; malabsorption occurs when lactase activity is insufficient
  • Fructans and galacto-oligosaccharides — in wheat, onions, garlic, legumes; ferment readily
  • Fructose in excess of glucose — in honey, apples, mangoes, agave syrup; exceeds GLUT5 transport capacity
  • Polyols — sorbitol, mannitol, xylitol, erythritol; in stone fruit and sugar-free products

The unabsorbed carbohydrate reaches the colon, where bacteria ferment it to produce hydrogen and methane gas, short-chain fatty acids, and osmotic fluid shifts — generating the characteristic bloating, distension, borborygmi, and altered bowel habit.

Lactose intolerance in Australia

The RACGP AFP review by Barrett and Gibson (2012) notes that primary (adult-onset) lactase non-persistence is the most common subtype — genetically determined decline in lactase activity after weaning. Australian prevalence is strongly ethnicity-dependent: approximately 10–25% of Northern European background, rising to over 70% in East Asian, Aboriginal and Torres Strait Islander, Indigenous Pacific, and Mediterranean populations. Australia’s ethnic diversity means lactose intolerance is common across all practice settings.

Secondary lactase deficiency arises from small bowel mucosal injury — coeliac disease, acute gastroenteritis, Crohn’s disease, radiation, chemotherapy — and may be temporary if the underlying cause is treated.

Most adults with primary lactase non-persistence can still tolerate 12–15 g of lactose per day distributed across meals — roughly one cup of full-cream milk — without significant symptoms. Hard aged cheeses (cheddar, parmesan) contain very little lactose; yoghurt with live cultures is better tolerated because bacterial lactase reduces the load.

Fructose malabsorption

Approximately 30–40% of healthy adults malabsorb fructose at standard test doses, per Monash FODMAP research. This is not a disease — it reflects saturation of GLUT5 fructose transporters in the small bowel at high fructose loads. Foods with fructose in excess of glucose (apples, pears, mangoes, watermelon, honey, agave syrup, high-fructose corn syrup) are most problematic; foods where glucose and fructose are present in roughly equal proportions (bananas, citrus, berries, kiwifruit) are usually tolerated.

The first step — exclude coeliac disease

Before attributing any bloating, loose stool, or abdominal symptoms to FODMAP intolerance, coeliac disease must be actively screened for. Therapeutic Guidelines (eTG) and the Gastroenterological Society of Australia are clear on this: coeliac disease causes secondary lactase deficiency and produces an identical clinical picture to FODMAP intolerance. Treating with a FODMAP-restricted diet (which often incidentally restricts wheat) without coeliac serology means the underlying diagnosis is missed and mucosal damage continues.

Testing requires tTG IgA and total IgA while the patient is still eating a gluten-containing diet. Total IgA is essential to identify the ~2% of patients with IgA deficiency who will give a falsely negative tTG result. Patients who have already self-excluded wheat must be asked to reintroduce gluten for at least 6 weeks before serological testing — this conversation should happen before dietary exclusion wherever possible.

Faecal calprotectin is indicated when there has been any change in bowel habit in an adult over 45, when bleeding has been reported, or when inflammatory bowel disease needs exclusion.

Investigations

Always do before labelling carbohydrate intolerance:

  • FBC, ferritin, B12, folate, U&E, calcium, vitamin D, TSH
  • tTG IgA + total IgA — coeliac screen
  • Faecal calprotectin if change in bowel habit, rectal bleeding, or any red flag

Hydrogen/methane breath testing: Available at private pathology laboratories for lactose (25 g test) and fructose (35 g test); a rise of ≥20 ppm above baseline confirms malabsorption. There is no MBS item number for breath testing — patients pay $80–150 per substrate out of pocket. Testing is most useful when the result will specifically change management; for most patients, clinical history and empirical dietary trial are sufficient.

Red flags that redirect away from FODMAP workup

Weight loss, iron deficiency anaemia, blood per rectum, nocturnal symptoms, fever, family history of coeliac disease or inflammatory bowel disease, or symptom onset after age 50 — all require investigation for organic disease before a functional diagnosis is applied.

B. Management — the three-phase low-FODMAP approach

The Halmos et al. RCT (Gastroenterology 2014) — conducted at Monash — demonstrated that a low-FODMAP diet produced significantly greater symptom reduction than a standard Australian diet in people with IBS. Approximately 50–70% of patients with FODMAP-responsive symptoms achieve meaningful relief during the elimination phase. The ACG 2021 IBS guideline and BSG 2021 IBS guideline both conditionally recommend dietary FODMAP restriction as a management option.

Phase 1 — Elimination (4–6 weeks): Strict low-FODMAP eating removes all major FODMAP subgroups. Symptom response in this phase is the diagnostic test — if symptoms do not substantially improve, FODMAP is unlikely to be the dominant driver. Stopping at this point and reconsidering is appropriate.

Phase 2 — Structured reintroduction (6–8 weeks): One FODMAP subgroup is reintroduced at a time in increasing quantities, with symptom monitoring. This phase identifies the patient’s individual tolerance map. Most patients find they react to specific subgroups at specific doses, not to all FODMAPs equally.

Phase 3 — Personalisation: The patient eats as broadly as possible, restricting only the specific identified triggers. The goal is the least restrictive diet compatible with symptom control, supporting gut microbiome diversity and ensuring adequate calcium, fibre, and micronutrient intake.

A Monash-trained dietitian is strongly recommended for this process. Unsupervised long-term FODMAP restriction without reintroduction causes measurable reduction in bifidobacteria diversity, risks calcium deficiency (particularly if dairy is also reduced), and is associated with disordered eating patterns in vulnerable individuals. The Gastroenterological Society of Australia and Monash consistently recommend dietitian involvement for any structured FODMAP work.

C. Specific management for lactose intolerance

For primary lactase non-persistence, complete dairy elimination is not necessary or advisable for most adults. Per eTG and AMH:

  • Most adults tolerate 12–15 g lactose per day (approximately one glass of milk) distributed across meals with food
  • Lactose-free and lactose-hydrolysed dairy products (Zymil, Liddells, Pauls Zymil) maintain calcium and protein intake
  • Lactase enzyme tablets (Lacteeze, Digestaid Lactase) taken with the first bite of dairy reduce symptoms dose-dependently — a practical solution for occasional dairy exposure
  • Hard aged cheeses and live-culture yoghurt are better tolerated and should be retained
  • Calcium adequacy must be maintained: if dairy is substantially reduced, calcium-fortified soy or oat milk and dietary sources (sardines, tofu, leafy greens) are essential. Adults require ≥1000 mg calcium per day; women over 50 require ≥1300 mg

D. Australian operations

MBS items: Standard GP consultations (items 23, 36, 44). Coeliac serology (tTG IgA + total IgA) and the initial blood panel are standard pathology items. Gastroscopy with duodenal biopsy for coeliac confirmation is item 30473. Colonoscopy if the differential requires it is item 32222. Allied health under a GP Chronic Condition Management Plan (items 965/967) funds five dietitian visits per calendar year (item 81120) — the most important referral for structured FODMAP management.

PBS prescribing: Antispasmodics (hyoscine/Buscopan, mebeverine/Colofac) are OTC or PBS general schedule for cramping. Loperamide (Imodium) is OTC. Low-dose amitriptyline (10–25 mg nocte) for visceral hypersensitivity is PBS general schedule (off-label indication at this dose). Lactase enzyme products are OTC and not PBS-subsidised.

Hydrogen breath testing costs: No MBS item. Private pathology $80–150 per substrate. The Monash FODMAP app (iOS and Android, AU-developed) provides current food FODMAP data and is an excellent patient self-management tool.

Mental Health Care Plan: For patients where anxiety or disordered eating is a significant driver of food-related distress, a Mental Health Care Plan (item 2715) with referral to a clinical psychologist provides access to gut-directed cognitive behavioural therapy or hypnotherapy, both of which have RCT evidence in IBS and FODMAP-overlap presentations.

E. Special populations

Pregnancy: Dietary modification for symptom management is appropriate. Breath testing and pharmacological adjuncts are generally deferred. Calcium adequacy is especially important during pregnancy and breastfeeding — low-lactose dairy and fortified plant milks should be recommended if dairy is reduced.

Children and adolescents: FODMAP sensitivity is common in teenagers with functional gastrointestinal symptoms. Disordered eating risk is higher in this age group, and any dietary restriction in a young person should be supervised by a paediatric dietitian. Coeliac disease is more common in children than in adults and must be excluded.

Aboriginal and Torres Strait Islander patients: Prevalence of lactase non-persistence is high in many ATSI communities, and may be under-recognised as a cause of gastrointestinal symptoms. Calcium adequacy is an important consideration when recommending dairy restriction; calcium-rich alternatives must be discussed.

Elderly patients: Reduced lactase activity is common with advancing age. Calcium and vitamin D adequacy are critical to bone health — the dual priority of symptom management and bone protection requires careful dietary planning.

When to escalate

Refer to gastroenterology if:

  • Symptoms persist despite two structured dietary trials with dietitian support
  • Red flag features at any point — weight loss, anaemia, rectal bleeding, fever, nocturnal symptoms
  • Positive coeliac serology — for endoscopy and biopsy confirmation
  • Suspected SIBO (symptoms persist on strict diet; risk factors including prior bowel surgery, motility disorder)

Refer to an eating disorder team if there is significant food restriction, weight loss, social withdrawal from meals, or features of ARFID (Avoidant/Restrictive Food Intake Disorder).

What this article is and is not

This article draws on RACGP AFP guidance, Therapeutic Guidelines (eTG), the Monash University FODMAP Program, GESA, ACG 2021, and BSG 2021 guidelines. It is general health information for educational purposes and does not constitute personal medical advice or create a doctor–patient relationship.

For Australian consumer resources: HealthDirect — Lactose intolerance, Better Health Channel, Monash FODMAP, Coeliac Australia.

Sources cited

  1. RACGP AFP — Barrett and Gibson, Fructose and lactose testing 2012
  2. Therapeutic Guidelines (eTG) — Gastrointestinal
  3. Australian Medicines Handbook
  4. NPS MedicineWise — IBS prescribing
  5. Monash University FODMAP Program
  6. Gastroenterological Society of Australia (GESA)
  7. Coeliac Australia
  8. HealthDirect — Lactose intolerance
  9. Better Health Channel — Lactose intolerance
  10. Lacy BE et al. — ACG Clinical Guideline: IBS 2021
  11. Vasant DH et al. — BSG IBS Guidelines 2021
  12. Halmos EP et al. — Low-FODMAP RCT in IBS (Gastroenterology 2014)

Frequently asked questions

  • I'm bloated and gassy after dairy foods — is this lactose intolerance?

    It may be, but there are several other possibilities worth ruling out before assuming lactose intolerance. Coeliac disease, for example, damages the small bowel lining and produces exactly this pattern — and it is very important to test for it before starting any dietary restriction. Once coeliac and other causes are excluded, lactose intolerance is confirmed by symptom pattern (bloating, gas, loose stool 30 minutes to 4 hours after dairy) or by a hydrogen breath test. Many people with lactose intolerance can still tolerate small amounts of dairy — particularly hard cheeses, yoghurt, and lactose-free milk — without completely eliminating calcium-rich foods.

  • What are FODMAPs and why should I avoid them?

    FODMAPs are fermentable short-chain carbohydrates — lactose in dairy, fructans in wheat and onions, galacto-oligosaccharides in legumes, excess fructose in honey and some fruits, and polyols in stone fruit and sugar-free products. When these reach the colon unabsorbed, bacteria ferment them, producing gas and drawing water in, which causes bloating, cramping, and altered bowel habit. A low-FODMAP diet reduces symptoms in about 70% of people with irritable bowel syndrome, but the goal is not permanent avoidance — a structured reintroduction phase identifies which specific FODMAPs trigger your symptoms, so you can eat as broadly as possible.

  • If I cut out wheat and dairy I feel better — does that mean I'm coeliac or allergic?

    Not necessarily. Most people who improve when removing wheat and dairy are responding to the reduced FODMAP load (wheat contains fructans; dairy contains lactose) rather than to gluten or milk protein allergy. True coeliac disease requires serological testing (tTG IgA) while you are still eating gluten — if you have already eliminated wheat before testing, the result may be falsely negative. Cow's milk protein allergy is a separate IgE-mediated condition, quite different from lactose intolerance. Your GP can help sort out which category applies to you with a simple blood test and careful history.

  • Do I need a hydrogen breath test to diagnose lactose intolerance?

    Not necessarily — the diagnosis can be made clinically based on your symptom pattern in relation to dairy intake. The hydrogen breath test confirms malabsorption with a standard threshold, but it has reproducibility limitations and is not covered by Medicare (you pay $80–150 out of pocket per substrate). It is most useful when the result will genuinely change how you manage the condition — for example, whether to maintain a moderately reduced lactose diet or a fully lactose-free diet. For most people, an empirical two-to-four week dairy elimination followed by deliberate re-challenge with a glass of full-fat milk is an equally valid approach.

  • I have bloating and was told to try a low-FODMAP diet — can I do it on my own?

    The low-FODMAP diet has three phases — strict elimination for 4–6 weeks, then structured reintroduction of one FODMAP group at a time, then personalisation based on your individual triggers. The reintroduction phase is the most important and is difficult to do correctly without guidance. Staying on strict elimination long-term without reintroduction reduces gut microbiome diversity and risks calcium, fibre, and micronutrient shortfalls. A dietitian trained in the Monash FODMAP program (developed in Melbourne and the world standard for this approach) makes a substantial difference to outcomes. Medicare supports five allied-health visits per year through a GP Chronic Condition Management Plan.

Source quality

Sources grouped by evidence tier. AU primary tier first; international where AU is silent or lagging; named-author reconstruction where guidelines have not yet caught up. How tiers work.