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Lactose intolerance

BMJ 2007; 334 doi: https://doi.org/10.1136/bmj.39252.524375.80 (Published 28 June 2007) Cite this as: BMJ 2007;334:1331

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Lactose malabsorption is rarely a clinical problem

Approximately 20% of North Europeans and Americans, and the majority
of the world’s population malabsorb lactose, but most are asymptomatic.
Lactose malabsorbers do get symptoms of lactose intolerance -abdominal
cramps, bloating, flatulence and osmotic diarrhoea, if they ingest
excessive amounts of lactose, such as in the lactose tolerance test which
involves ingesting the lactose load (50g) found in 1 litre of cow’s milk,
on an empty stomach. However lactose malabsorption is rarely a clinical
problem in adults, since malabsorbers often recognise that excess dairy
products cause upset and modify their diet spontaneously without the need
for medical consultation. Furthermore, when lactose malabsorbers
chronically ingest lactose, (colonic) bacterial adaptation occurs with
increased tolerance for lactose [1].

The abdominal symptoms of lactose intolerance resemble those of
irritable bowel syndrome. The prevalence of lactose malabsorption in
irritable bowel syndrome is the same as in the general population [2].
Many irritable bowel syndrome patients either perceive themselves as
lactose malabsorbers when they are not [2], or blame their coincident true
lactose malabsorption for their symptoms despite evidence showing a poor
symptomatic response to dietary lactose withdrawal [3-5]. Even lactose
malabsorbers who consider themselves to be very lactose intolerant can
actually tolerate moderately large amounts (12-24 g) of lactose (1-2
glasses milk) daily without symptoms [6].

Despite these data, possible lactose malabsorption is often
frequently but futilely investigated in patients with irritable bowel
syndrome. Patients with irritable bowel syndrome and coincident lactose
malabsorption may make unnecessary efforts to avoid all lactose, including
lactose used to make up pills. Such misapprehensions about the role of
lactose in their symptom production are fuelled in some countries by a
multi-million dollar industry promoting unnecessary lactase enzyme
supplements and alternative milk products.

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1. Hertzler SR, Savaiano DA. Colonic adaptation to daily lactose
feeding in lactose maldigesters reduces lactose intolerance. Am J Clin
Nutr l996;64:232-36.

2. Vernia P, Marinaro V, Argnani F, Di Camillo M, Caprilli R. Self-
reported milk intolerance in irritable bowel syndrome: what should we
believe? Clin Nutr 2004; 23: 996-1000.

3. Suarez FL, Savaiano DA, Levitt MD. A comparison of symptoms after
the consumption of milk or lactose-hydrolyzed milk by people with self-
reported severe lactose intolerance. N Engl J Med 1995;333:1-4.

4. Tolliver BA, Jackson MS, Jackson KL, Barnett ED, Chastang JF,
DiPalma JA. Does lactose maldigestion really play a role in the irritable
bowel? J Clin Gastroenterol 1996; 23: 15-7.

5. Parker TJ, Woolner JT, Prevost AT, Tuffnell Q, Shorthouse M,
Hunter JO. Irritable bowel syndrome: is the search for lactose intolerance
justified? Eur J Gastroenterol Hepatol 2001; 13: 219-25.

6. Suarez FL, Savaiano D, Arbisi P, Levitt MD. Tolerance to the daily
ingestion of two cups of milk by individuals claiming lactose intolerance.
Am J Clin Nutr 1997;65:1502-6.

Competing interests:
None declared

Competing interests: No competing interests

05 July 2007
David A Gorard
Consultant Gastroenterologist
Wycombe Hospital, Bucks, HP11 2TT