Slideshows Images Quizzes
font size

Lactose Intolerance (cont.)

Medical Author:
Medical Editor:

What are the signs and symptoms of lactose intolerance?

The common primary symptoms of lactose intolerance are gastrointestinal and include:

Less common symptoms of lactose intolerance include:

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

Constipation is not a sign of lactose intolerance.

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 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 vary 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.

What foods have lactose and should be avoided in the diet?

Although milk and foods made from milk are the only natural sources of lactose, lactose often is "hidden" in prepared foods to which it has been added. People with very low tolerance for lactose should know about the many food products that may contain lactose, even in small amounts. Food products that may contain lactose include:

  1. Bread
  2. Baked goods
  3. Processed breakfast cereals
  4. Instant potatoes, soups, and breakfast drinks
  5. Margarine
  6. Lunch meats (except those that are kosher)
  7. Salad dressings
  8. Candies
  9. Chips and other processed snacks
  10. Mixes for pancakes, biscuits, and cookies
  11. Soft cheeses
  12. Milk
  13. Nondairy whipped toppings
  14. Nondairy liquid and powered coffee creamers

Smart shoppers learn to read food labels with care, looking not only for milk and lactose in the contents but also for such words as whey, curds, milk by-products, dry milk solids, and nonfat dry milk powder. If any of these are listed on a label, the item contains lactose.

What about lactase in medications or drugs?

In addition to food sources, lactose can be "hidden" in medicines. Lactose is used as the base for many prescription and over-the-counter medications. Many types of birth control pills, for example, contain lactose, as do some tablets used for stomach acid and gas. However, these products typically affect only people with severe lactose intolerance because they contain such small amounts of lactose.

Medically Reviewed by a Doctor on 10/28/2016


GI Disorders

Get the latest treatment options.

Use Pill Finder Find it Now See Interactions

Pill Identifier on RxList

  • quick, easy,
    pill identification

Find a Local Pharmacy

  • including 24 hour, pharmacies

Interaction Checker

  • Check potential drug interactions
Search the Medical Dictionary for Health Definitions & Medical Abbreviations

Health Solutions From Our Sponsors