Is my baby lactose-intolerant?

20 Jan

Written By George Du Toit

Lactose, a mammalian sugar and the reason infants love the taste of breast milk and explains why it is sometimes hard to find alternative milks for them.
Families will often ask in the clinic if their child is lactose intolerant.
It is extremely rare for infants to be born lactase-deficient.
A more common reason for lactose intolerance is transient intolerance, which occurs for a short while after a bout of diarrhoea, illness, or a course of antibiotics. Severe chronic illness that affects the GI tract can also cause this.
Lactase non-persistence in at-risk groups (in fact, in most humans) usually only appears with increasing age, not in infancy.

What are the symptoms and signs of lactose intolerance in infants?

The classic features of lactose intolerance in infants are:
- watery, acidic diarrhoea
- abdominal distension
- flatulence
- and, in severe cases, failure to thrive and dehydration if lactose-containing feeds are continued.
- Hives, immediate-onset rashes, and tissue swelling are features of CMPA, not lactose intolerance.
These symptoms typically occur after ingestion of breast milk or standard infant formula (both of which will contain lactose).
In congenital lactase deficiency (alactasia), symptoms present soon after initiation of feeds, with persistent diarrhoea leading to weight loss and risk of severe dehydration. This is EXCEPTIONALLY RARE!
In the more common secondary lactose intolerance (e.g., post-infectious or due to mucosal injury), symptoms are similar but may be less severe and are often transient. Abdominal pain, bloating, and increased stool frequency are also common features.
The onset of symptoms is temporally related to lactose ingestion and resolves with the removal of lactose from the diet. Whilst breast milk contains lactose, there is no reason to stop it, as transient lactose intolerance will soon resolve.
There are numerous lactose-free infant formulae for infants who develop lactose intolerance, e.g., Rice- and soy-based infant formulae.
Our team is experienced at assisting you through what can be a difficult diagnostic process.

Frequently Asked Questions

- Many people do not know that human milk has the highest lactose concentration, typically around 6.7–7.0 g per 100 mL (67–70 g/L).
- In comparison, cow's milk has a lower lactose content, averaging about 4.6–4.9 g per 100 mL (or 46–49 g/L).
- Most infant formulas in the United Kingdom are designed to mimic human milk, and their lactose content is generally similar to or slightly lower than that of human milk, typically ranging from 4.5 to 7 g per 100 mL (45–70 g/L), depending on the brand and formulation.
1. Clinical history, dietary elimination and rechallenge can be used for diagnosis in infants: resolution of symptoms with lactose elimination and recurrence with reintroduction supports the diagnosis, especially in infants where formal testing is difficult.
2. Hydrogen breath test (HBT) is the most widely used and recommended non-invasive diagnostic method for lactose intolerance in older children. It involves administering an oral lactose load (typically 1–2 g/kg, up to a maximum of 25 g) and measuring breath hydrogen at intervals. An increase in breath hydrogen ≥20 ppm above baseline is considered diagnostic for lactose malabsorption. The test is interpreted in conjunction with the presence of symptoms during or after the test, as symptom correlation is essential for diagnosing lactose intolerance rather than just malabsorption.
3. Symptom assessment after lactose challenge is critical. Validated symptom questionnaires or direct observation of symptoms (such as diarrhea, abdominal pain, bloating, or flatulence) following a lactose load are used to confirm clinical intolerance, as malabsorption and symptoms do not always correlate.
4. Genetic testing for lactase non-persistence (C/T-13910 polymorphism) may be considered, especially in populations with a high prevalence of lactase persistence or in cases where the breath test is not feasible. However, genetic testing identifies predisposition to primary lactase deficiency but does not confirm current intolerance or secondary causes, which are more common in infants.
5. Stool acidity and reducing substances may be used as supportive tests in infants, especially when breath testing is not feasible. Acidic stools (pH <5.5) and the presence of reducing substances suggest carbohydrate malabsorption but are not specific for lactose.
- Ethnic groups worldwide at increased risk for developing lactose intolerance include East Asian, West African, Arab, Jewish, Greek, Italian, Hispanic/Latino, Native American, and most Indigenous Australian and Pacific Islander populations.
- In these groups, the prevalence of lactase non-persistence (and thus lactose intolerance) ranges from 70% to nearly 100% in adulthood, with the highest rates observed in East Asian and Native American populations.
- In contrast, Northern Europeans (e.g., Scandinavian, British, Irish) have the lowest prevalence of lactose intolerance, with lactase persistence rates exceeding 90% in some populations.
- Lactose intolerance, if it does develop, in at risk populations, usually presents after age 5, as lactase enzyme activity begins to decline following weaning.
- The onset of symptoms is most common in mid-childhood to adolescence, although the exact age can vary depending on genetic background.
- In populations with high rates of lactase non-persistence, the decline in lactase activity and the emergence of symptoms may occur as early as 5–7 years of age.
Breastfeeding should be continued wherever possible, as human milk is generally well tolerated except in the exceptionally rare cases of congenital lactase deficiency.
For lactose intolerant infants, the recommended infant formulas are rice or soy-based infant formulae, or lactose-free cow’s milk protein-based formulas.
Lactose-free formulas are generally nutritionally complete and use alternative carbohydrates such as glucose polymers or corn syrup solids instead of lactose. These formulas are appropriate for infants with congenital lactase deficiency or secondary lactose intolerance (e.g., post-gastroenteritis) who are not breastfed and do not have cow’s milk protein allergy.
Soy-based formulas are not recommended as first-line for infants under 6 months due to concerns about phytoestrogen exposure and are contraindicated in infants with confirmed cow’s milk protein allergy due to the risk of coexisting soy allergy.
Extensively hydrolyzed or amino acid-based formulas are not indicated for isolated lactose intolerance but are reserved for infants with cow’s milk protein allergy.

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