Originally Published: October 30, 1998 - Last Updated / Reviewed On: December 17, 2010
(1) Hi Alice,
For some years I did not drink milk, but started to take a lot of milk just recently and discovered I cannot digest milk without developing a lot of gas, stomach aches, etc. I did not have that problem before I stopped drinking milk. Will I develop more lactase, i.e., the ability to digest milk, as time goes on and I drink more milk, or will I have to take Lactaid milk for the rest of my life (it's not available in some countries).
What are the symptoms of lactose intolerance (i.e., how long after taking a milk product will symptoms generally begin, and what are the typical symptoms), and how do they differ from irritable bowel syndrome?
Dear Readers #1 and 2,
Lactose intolerance is a very common condition in which the milk sugar lactose cannot be digested because of a partial or full deficiency of the lactase enzyme that's needed to break it down. With lactose intolerance, whatever lactose remains undigested in the intestines attracts water, which results in diarrhea. Some of the undigested lactose is broken down by normal intestinal bacteria as it makes its way to the rectum. This can lead to gastrointestinal (GI) discomfort, bloating, gas, and cramps. These symptoms usually occur within a half-hour to two hours of ingesting a lactose-containing food.
In general, the amount of lactase normally available in our intestinal gut declines as we age. That is, we become less and less able to break down lactose as we grow older. Although people cannot naturally produce more lactase, most lactose intolerant people can handle some lactose in their diet without any symptoms. Some may even be able to improve their lactose tolerance (to as much as twelve grams of lactose, the amount that's found in one eight-ounce glass of regular, non-lactose reduced milk) by gradually consuming more and more dairy products so that their bodies can slowly adapt to this change. Many lactose intolerant people also seem to have no problems after consuming fermented dairy products, such as aged hard cheeses, yogurt, and cottage cheese. (The bacteria used to ferment these foods digest the lactose that's in them, making them more tolerable.)
Of course, the only way to avoid the symptoms of lactose intolerance is to not eat any foods containing lactose. This is not an easy thing to do if you already love dairy products (nondairy substitutes are available, such as milk, cheese, frozen desserts, yogurt, cottage cheese, etc. made with soy and/or rice). It's also tricky because some nondairy foods, such as breads, cereals, snacks, salad dressings, and cake mixes, also contain lactose. Carefully read the ingredients on food labels. Besides lactose itself, look for milk, milk solids, whey (milk liquid), and casein (milk protein), which all contain lactose to some degree. Some prescription and over-the-counter drugs and nutritional supplements also contain lactose. Ask your pharmacist for more information.
If you choose not to cut out lactose-containing foods from your diet, try commercially available lactose-reduced products, such as Lactaid milk (which tastes a bit sweet because the lactose sugar has already been broken down to make it digestible) and lactase enzyme supplements. These supplements are available as pills or drops, which can be added to milk, and they help many lactose intolerant people handle more lactose in their diet. At first, take the amount suggested by the manufacturer with meals containing lactose. If you still experience symptoms, you'll need to use trial and error before finding out how much is enough for you to remain symptom-free. You may also need to use more when eating a quantity larger than usual, or when consuming a non-fermented dairy product, such as ice cream, soft cheeses, milk, and creamy foods.
The biggest nutritional concerns for lactose intolerant people are how to meet their calcium and riboflavin (a B vitamin) needs. For a list of nondairy sources of calcium, read
Although lactose intolerance shares some of the symptoms of Irritable Bowel Syndrome, such as abdominal pain and discomfort, gas, bloating, and diarrhea, they are two different conditions. Irritable Bowel Syndrome (IBS) is a common, chronic digestive problem that's characterized by impaired muscular contractions of the large intestine, resulting in alternating bouts of diarrhea and constipation. IBS may be caused by emotional stress, a low-fiber diet, and/or an intolerance to certain foods. IBS sufferers tend to have difficulty digesting fats, not necessarily dairy foods (unless they are also lactose intolerant). For more information about Irritable Bowel Syndrome, read Spastic colon and More on irritable bowel syndrome in