Doctor's Desk

Lactose Intolerance 

is the manifestation of symptoms resulting from malabsorbed lactose, causing diarrhoea  nausea, flatulence, abdominal pain and/or bloating, occurring 30 to 120 minutes of lactose ingestion. 


Lactose Intolerance Pathophysiology 

1. Congenital lactase deficiency

Is a genetic disorder resulting in reduced lactase synthesis at birth. This condition requires lifelong lactose avoidance.  A small intestinal biopsy may show normal villi but low or absent lactase concentrations. 


2. Developmental Lactase Deficiency

Developmental lactase deficiency is a relative absence of lactase activity in infants less than 34 weeks’ gestation.

3. Primary Lactase Deficiency

Primary lactase deficiency, the most common form of lactose intolerance, is a relative or absolute absence of lactase present in the digestive tract. It is also known as adult-type hypolactasia, lactase non-persistence or hereditary lactase deficiency. However, this deficiency occurs more commonly over a period of several years, beginning from childhood to adulthood. 


4. Secondary Lactase Deficiency

Secondary lactase deficiency is the result of an underlying pathophysiology resulting in lactose deficiency and subsequent malabsorption. Pathologies include infection (rotavirus, giardiasis, cryptosporidiosis), celiac disease, Crohn’s disease, and enteropathies resulting in small intestinal injury. Small intestinal injury results in reduced production of lactase and continues throughout new immature epithelial cell development. Severe malnutrition can also result in intestinal atrophy, resulting in reduced lactase production. 

Diagnosis of Lactose Intolerance 

Tests and assessments include:

  • Hydrogen Breath Test: The hydrogen breath test is a non-invasive method of measuring lactose malabsorption.  This test involves the consumption of an oral lactose dose from 25-50 grams by fasted individuals. 

  • Direct Assessment of Lactase Levels: Direct assessment of lactase levels can be performed through a biochemical assay of a jejunal tissue sample (less commonly used as invasive).


  • Trial of Lactose-free DietIndividuals suspected of being lactose intolerant may choose to trial a lactose-free diet. This includes the elimination of major and hidden sources of lactose for a two-week period. Resolution of symptoms including abdominal pain, distension, flatulence, cramping and diarrhea may be suggestive of lactose intolerance.

Doctor and Patient
Fruit and Granola

Dietary management of Lactose Intolerance 

Diet modification plays a key role in the management of this conditions, symptoms and nutritional adequacy. 

  • Elimination diet - Lactose free / low lactose 

  • Micronutrient optimisation (Calcium and Vitamin D)

  • Nutritional adequacy (protein and calories) 

  1. Gastrointestinal System - Lactose Intolerance Background. 2018. PEN. 

  2. Food Sources of Lactose. 2021. PEN. Patient education handout. 


For individualised advice, book in now at the Dietetic Gut Clinic 


St Luke Medical Centre 
1/57 Burroughs Rd, Karrinyup  WA 6018

© 2021 Dietetic Gut Clinic