Ignoring the possibility that comorbidities influence symptoms in patients with carbohydrate malabsorption
Abdominal pain, bloating and a variable bowel habit are nonspecific symptoms that can occur with various functional or organic diseases, with or without carbohydrate malabsorption. In particular, intolerance of numerous foods is a hallmark of irritable bowel syndrome (IBS).27 Potential comorbidities must be considered to better understand the treatment options for patients who have these symptoms.
Patient history may provide a clue towards understanding the pathogenesis of their symptoms. Those who have food intolerances with a defined aetiology, such as primary lactase deficiency, tend to have discrete symptoms that occur only after ingestion of the respective food. By contrast, those who have a functional aetiology, such as IBS, often complain of multiple gastrointestinal and other symptoms that change over time (e.g. dyspepsia, chronic headache and fibromyalgia).28,29
There is a large overlap between the occurrence of lactose malabsorption and IBS, both of which are common conditions worldwide. Altering dietary intake of fermentable carbohydrates, including lactose in patients with lactase deficiency, is known to alter symptoms in IBS.30 In this condition, the risk of developing symptoms after lactose ingestion is related not only to the dose of lactose ingested but also to patient factors.31 These factors include a history of abdominal surgery or recent gastrointestinal disease,32 evidence of an activated mucosal immune system (e.g. increased mast cells in biopsy samples from the small intestine and colon),33 the presence of SIBO22 and colonic dysbiosis (as determined by excessive hydrogen production during a lactose hydrogen breath test [HBT]).31,34 Psychosocial factors, such as the presence of psychological disease and/or high levels of ‘life event stress’, are also important.32 Many of these factors, especially inflammation and anxiety, are associated with visceral hypersensitivity in patients with IBS.
In individuals with lactose malabsorption various somatic and psychosocial factors impact on the risk of symptom development after ingestion of small to moderate amounts of lactose (i.e. clinically relevant lactose intolerance). The shared aetiology of these conditions suggests that lactose intolerance is a form of functional bowel disease and, indeed, food intolerance is recognized as an important cause of symptoms in many IBS patients.31
In lactose or fructose intolerant patients whose symptoms persist while on an exclusion diet, other factors and diseases contributing to the pathogenesis of symptoms have to be considered and treated accordingly, typically the functional bowel disorders IBS and functional dyspepsia. A reduction of FODMAPs in the diet has been shown to reduce symptoms in patients with IBS.35,36
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