The connection between dairy and IBS can take the form of lactose intolerance and the insufficiency of lactase enzymes leading to the incomplete digestion of dairy leading to GI symptoms. Another connection and cause of symptoms may be an allergy or intolerance to the casein protein in dairy.

Lactose intolerance

Lactose intolerance symptoms primarily impact the GI tract. Lactase enzyme is designed to decode the lactose molecule into its two designer molecules: glucose and galactose. If that magic interaction doesn’t occur — that is, if you’re one of millions of people who don’t produce lactase enzymes — lactose continues merrily along the superhighway of your gut wreaking havoc in its path.

The chaos is due to bacteria and yeast in your large intestine feasting on undigested milk sugar, resulting in many IBS-like symptoms.

Symptoms of lactose intolerance include abdominal bloating, distention, pain and cramping, audible bowel noises, diarrhea, flatulence (passing gas), and sometimes nausea. These symptoms can be confused with an intestinal infection or celiac disease or be labeled IBS or IBD (inflammatory bowel disease).

Symptoms differ at different ages. Children with lactose intolerance may also have failure to thrive because one of their main sources of nutrients isn’t being absorbed and they’re losing nutrients due to diarrhea.

Remember the childhood birthday parties where cake and ice cream (or ice cream cake) were the main attraction? Imagine how scary and embarrassing those are for a child who’s blindsided by a need to rush to the bathroom while the other kids are pinning the tail on the donkey.

Adults may have the symptoms along with an urgency to evacuate the bowels. The timing can be from 30 minutes to two hours after a meal containing lactose.

According to the National Digestive Diseases Information Clearinghouse (NDDIC), 30 to 50 million Americans are lactose intolerant. But different cultures experience different levels of intolerance. 90 to 100 percent of Asian Americans, 80 percent of African Americans, and 15 percent of Caucasians suffer from the condition. Folks of northern European descent have even lower rates of lactose intolerance.

The symptoms associated with lactose intolerance are often related to the amount of dairy consumed and vary from one individual to another. If you eat dairy as the bulk of your meal or snack instead of it being a small portion of your meal, you may have a more difficult time digesting it.

However, having milk or cheese as part of a full meal, which allows for a longer digestion time, give your limited lactase enzymes more time to do their work. Some dairy products also contain less lactose and are often easier to tolerate.

Casein allergy or intolerance

Casein is a milk protein, whereas lactose is a milk sugar. The symptoms of a casein allergy or intolerance are more difficult to identify as coming from dairy. Symptoms can include GI symptoms (vomiting, heartburn, abdominal pain, diarrhea, gas, and bloating) and also eczema, hives, asthma, and shortness of breath.

Many foods that are advertised as “nondairy” or “dairy-free” still contain casein, and it may be found in high-protein or protein-enriched products. But casein can be hard to recognize on an ingredient list because it goes by several different names. Look for casein (obviously) but also sodium caseinate, galactose, sodium lactylate, lactose, lactalbumin, and other names that begin with or feature lact–.