Lactose Intolerance - Symptoms

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The symptoms of lactose intolerance can vary greatly from patient to patient. What were your symptoms at the onset of your disease?

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What are the symptoms of lactose intolerance?

The common primary symptoms of lactose intolerance are gastrointestinal include:

  • abdominal pain,
  • diarrhea, and
  • flatulence (passing gas).

Less common symptoms of lactose intolerance include:

  • abdominal bloating,
  • abdominal distention, and
  • nausea.

Unfortunately, these symptoms can be caused by several gastrointestinal conditions or diseases, so the presence of these symptoms is not very good at predicting whether a person has lactase deficiency or lactose intolerance.

Symptoms occur because the unabsorbed lactose passes through the small intestine and into the colon. In the colon, one type of normal bacterium contains lactase and is able to split the lactose and use the resulting glucose and galactose for its own purposes. Unfortunately, when they use the glucose and galactose, these bacteria also release hydrogen gas. Some of the gas is absorbed from the colon and into the body and is then expelled by the lungs in the breath. Most of the hydrogen, however, is used up in the colon by other bacteria. A small proportion of the hydrogen gas is expelled and is responsible for the increased flatulence (passing gas). Some people have an additional type of bacterium in their colons that changes the hydrogen gas into methane gas, and these people will excrete only methane or both hydrogen and methane gas in their breath and flatus.

Not all of the lactose that reaches the colon is split and used by colonic bacteria. The unsplit lactose in the colon draws water into the colon (by osmosis). This leads to loose, diarrheal stools.

The severity of the symptoms of lactose intolerance varies greatly from person to person. One reason for this variability is that people have different amounts of lactose in their diet; the more lactose in the diet, the more likely and severe the symptoms. Another reason for the variability is that people have differing severities of lactase deficiency, that is, they may have mild, moderate, or severe reduction in the amounts of lactase in their intestines. Thus, small amounts of lactose will cause major symptoms in severely lactase deficient people but only mild or no symptoms in mildly lactase deficient people. Finally, people may have different responses to the same amount of lactose reaching the colon. Whereas some may have mild or no symptoms, others may have moderate symptoms. The reason for this is not clear but may relate to differences in their intestinal bacteria.

Return to Lactose Intolerance

See what others are saying

Comment from: Britgal, 7-12 Female (Caregiver) Published: October 31

My 11 year old daughter has very bad stomach pain. She describes the feeling as being punched in the stomach. She has had chronic stomach pain for years which was diagnosed as chronic constipation. About 2 years ago I realized milk products made her pain worse. She had 2 great pain free years without dairy. However, now her stomach pain has returned and again I am trying to figure out what is causing it. Eating seems to cause her pain and she feels full after a few bites.

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Comment from: Denise, 55-64 Female (Caregiver) Published: November 18

Since visiting a relative's dairy farm end of August, my husband has been experiencing pain in his esophagus area. While on the farm, he consumed a large amount of raw milk and became ill (severe diarrhea) for a day and a half before we left for home. He thought the problem was either upper GI (gastro intestinal) or cardiac because of where the pain is. He's been hospitalized and had every test imaginable since then and all the results are negative. Yesterday, his doctor asked him to eliminate his lactose intake and journal for a week.

Was this comment helpful?Yes

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