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What is lactose? 

Lactose is the sugar found in milk. The body breaks it down to glucose and galactose.

What is lactose intolerance? 

Lactose intolerance is the inability to break down lactose in the small intestine. The enzyme lactase is needed to break down the carbohydrate lactose into glucose and galactose in the small intestine. As we age, the small intestine makes lower levels of lactase. When the small intestine does not produce sufficient amounts of lactase, this can cause lactose intolerance. When lactose can’t be digested or broken down in the small intestine, it travels to the large intestine where it is broken down by the bacteria in the gut. As bacteria breaks down lactose, gas is produced as a byproduct. The presence of lactose in the large intestine can cause an osmotic imbalance, pulling water into the large intestine and causing diarrhea. 

What are symptoms of lactose intolerance? 

When an individual with lactose intolerance consumes lactose, they may experience unpleasant digestive symptoms. Some of the most common symptoms of lactose intolerance include gas, bloating, abdominal pain, nausea, and diarrhea. 

The best way to treat lactose intolerance is by limiting or avoiding foods that contain lactose. Some individuals may need to eliminate lactose completely, while others may be able to tolerate up to 12g of lactose (about 1 cup of milk) in one sitting without any symptoms. Everyone’s tolerance will be different, as the lactase enzyme activity will vary from person to person. 

Can I become lactose intolerant overtime?  

Infants have high lactase activity, as this is the main carbohydrate in breastmilk. However as humans age, lactase activity decreases a few years after weaning from breastmilk. This diminishing lactase activity can lead to lactose intolerance. Another reason why someone might become lactose intolerant overtime is because of another illness or condition. This is referred to as secondary lactose intolerance. Infection in the stomach and intestines, inflammatory bowel disease, irritable bowel syndrome, celiac’s disease, and long course doses of antibiotics can all lead to lactose intolerance. 

What foods should be avoided with lactose intolerance? 

Individuals with lactose intolerance are recommended to avoid lactose containing foods, specifically dairy products. However, this does not mean you need to avoid all dairy products. Most individuals with lactose intolerance can tolerate a small amount of lactose throughout the day. 

Low lactose-dairy foods you might be able to tolerate in small amounts include aged cheeses such as Swiss cheese and parmesan, cream cheese, sour cream, and Greek yogurt. 

Dairy products high in lactose to avoid include milk, ice cream, coffee creamer, soft cheeses, and cheese spreads. When avoiding dairy products, it is important to replace important nutrients that we get from dairy such as vitamin D and calcium. Consider a vitamin D supplement and eat foods rich in calcium such as dark leafy green vegetables, fish with bones, tofu, and fortified breads and juices.

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Photo of Kristin Ricklefs-Johnson

Medically reviewed by:

Kristin Ricklefs-Johnson, Ph.D., RD

Kristin is an RDN who also earned her Ph.D. in Nutrition from Arizona State University with an emphasis on insulin resistance, lipid metabolism disorders, and obesity. She completed her post-doctoral fellowship at Mayo Clinic where she focused on nutrition-related proteomic and metabolic research. Her interests include understanding the exact mechanism of action of various genetic variations underlying individual predispositions to nutrition-related health outcomes. Her goal is to help all individuals prevent chronic diseases and achieve long, healthy lives through eating well.

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