It’s estimated that up to 65 percent of the world’s population has some degree of lactose intolerance, which is an inability to metabolize lactose effectively. Lactose is a sugar found in milk and other dairy products. In some people, the condition only produces mild discomfort, while in others, it can produce more severe symptoms that can interfere with quality of life. 

It is important to note that lactose intolerance is not an actual allergy to milk. It just means that the person produces too little of an enzyme known as lactase, which is what metabolizes lactose. Like other allergies, milk allergies can be extremely dangerous–even deadly–and are much different than lactose intolerance. A milk allergy is when the body responds to the proteins in milk as opposed to the sugar. An allergy such as this could result in anaphylactic shock. Lactose intolerance has different, more digestive symptoms, and while they can be disruptive, symptoms are not usually particularly harmful. 

Read on to learn more about the symptoms of lactose intolerance, how to tell the difference between lactose intolerance and irritable bowel syndrome (IBS), and how to find alternatives to dairy for nutrients.

Symptoms of Lactose Intolerance

Symptoms of lactose intolerance are generally not seen in children; however, it is essential to note that children could be allergic to milk, which, as stated above, is entirely different. Children are not lactose intolerant because they naturally seem to be able to produce enough lactase, the enzyme needed to metabolize lactose. Lactose is found in breast milk and formula and is well-tolerated by nearly all children. However, as people get older, they may have more trouble producing enough lactase, which can cause symptoms of lactose intolerance. In fact, by adulthood, up to 70 percent of adults may struggle with lactase production. Some of the most common symptoms include stomach pain and bloating, increased gas, diarrhea, and constipation.

-Stomach Pain and Bloating

Lactose is a sugar and is, therefore, a carbohydrate; so, if the body is producing enough lactase, the lactose is broken down, passes through the gut and then through the colon. If it is not broken down properly, it “hangs” in the colon and is fermented by the microflora. This releases gases and short-chain fatty acids, which can cause stomach discomfort and bloating. The stomach may also feel distended. The amount of pain and cramping or bloating isn’t tied to how much lactose or milk product is ingested; instead, it has more to do with the lactose sensitivity of the patient. In severely sensitive people, it may even cause nausea and vomiting, and in these patients, dairy products should be avoided.

-Increased Gas

As the lactose “hangs” in the small intestine for too long, being fermented by the microflora, this also causes an amount of increased gas. In fact, the gases released in the colon by this fermentation are methane, hydrogen, and carbon dioxide. As opposed to other types of flatulence or gas problems patients may experience, gas problems as they relate to lactose intolerance do not have an odor. The amount of gas produced depends on several factors: the absorption rate of gas in the colon as well as the efficiency of the microflora to ferment the lactose. More efficient fermentation leads to a lesser amount of gas.


Again, because of the fermentation of lactose in the colon, extra water may be produced in the colon, which may lead to diarrhea. The short-chain fatty acids created by the microflora are reabsorbed, which creates more liquidy and frequent stools. However, it’s important to note that an assumption of lactose intolerance shouldn’t be based on diarrhea alone. There could be many causes for diarrhea; however, diarrhea, in conjunction with other symptoms, could be a good indicator of a lactose intolerant patient.


Just like diarrhea may be an indicator of lactose intolerance for some, constipation may be a marker for others. Constipation is a lesser-known sign of lactose intolerance, but it still is a possibility. While the microflora fermentation releases methane and short-chain fatty acids, short-chain fatty acids can cause diarrhea, while methane can cause constipation in some patients. There can also be many other causes of constipation, so it’s always best to check with your healthcare provider to be sure about what is causing your digestive upset.

-Other Symptoms

The most common symptoms of lactose intolerance are cramping and bloating, gas, diarrhea, and constipation, however, there may be other markers that are important to tell your doctor. Other lesser-known, but possible, signs of lactose intolerance may include:

  • Fatigue
  • Brain fog
  • Eczema 
  • Headaches
  • Mouth ulcers or pain
  • Muscle stiffness or joint pain
  • Problems with urination

Some of the above symptoms are also correlated with milk allergy, and it is possible to have both lactose intolerance and a milk allergy. If you’re seeking the help of a medical professional, especially in the case of a child, it’s important to tell the physician about any problems with a skin rash, asthma, or eczema after milk products are consumed, as this may be more indicative of a milk allergy than lactose intolerance. But, it’s best to give your physician all of the information so they can make the best diagnosis. 

What Are the Differences Between IBS and Lactose Intolerance?

Irritable bowel syndrome (IBS) and lactose intolerance can sometimes have almost identical symptoms, so it may be impossible to tell the difference if you’re trying to discern on your own why you have digestive disturbances. It’s best to ask your doctor for advice. However, there are subtle differences between the two conditions, even though the symptoms are similar. One of the main differences is that lactose intolerance often causes nausea up to one to two hours after consuming dairy, while IBS does not. Also, doctors are not entirely sure what causes IBS, while research can clearly pinpoint why lactose is not being metabolized correctly – because the body loses the ability to produce enough lactase over time. 

What your doctor can do is provide you with a hydrogen breath test to give you a definitive diagnosis. Remember that undigested lactose emits hydrogen, methane, and carbon dioxide. What your doctor will ask you to do is to breathe into a bag. The air within the bag is then tested for higher-than-normal levels of hydrogen, which is indicative of undigested lactose. This is the best way to tell if you have IBS or lactose intolerance if you are unsure. Treatments are slightly different for the two conditions, so if your symptoms are moderate to severe, it’s imperative to find out to better your quality of life. 

Alternatives to Dairy

Patients that are lactose intolerant enough to have to avoid dairy often worry that they won’t get enough vitamin D, calcium, or other nutrients in their diet, but that isn’t so. There are plenty of foods out there that can help you receive your nutrients without consuming milk or dairy products. Also, for many who are lactose intolerant, they can consume some dairy products in small amounts occasionally. Most patients with lactose intolerance can still consume up to 12 grams of lactose per day, which is equal to one cup of milk.

If you are looking for alternative sources to calcium, opt for foods such as nuts, quinoa, seaweed, kale, broccoli, fortified orange juice, okra, and beans. 

For vitamin A-rich foods, try spinach, peas, papaya, mango, sweet potatoes, and carrots.

One of the best ways to get vitamin D is exposure to natural sunlight. Obviously, this isn’t always an option, so opt for eggs, fatty fish, or milk, such as almond or soy milk. If you need more information on lactose intolerance or IBS or would like to be seen by a physician, book an appointment with Asheville Gastroenterology Associates today. Our knowledgeable and caring staff provides the highest level of individualized and comprehensive digestive and gastrointestinal care.