How Lactose Fits Into (and Complicates) Your Diet

Not all foods we eat are broken down in the same way, and that’s especially true for lactose. This complex, natural sugar is found in all mammalian milk — from breast milk to cow’s milk and even goat milk. But its complexity gives it unique benefits and simultaneously makes it hard to break down or digest for anyone who’s lactose intolerant.

Gastroenterologist Christine Lee, MD, gives the 101 on lactose, what it does for your body, how it’s broken down and what happens when your body just can’t handle it.

What does lactose do for your body?

Lactose is a disaccharide — meaning it’s a complex sugar formed from two monosaccharides (or simple sugars). As a component of breast milk, it’s long been associated with numerous benefits:

• It helps your body absorb minerals like calcium, magnesium and zinc — all of which are important for bone health.
• It has a lower glycemic index when compared to simple sugars, meaning it helps you feel full longer and doesn’t cause extreme changes in blood sugar.
• It has prebiotic effects by helping good bacteria thrive inside your gut microbiome.
• It supports your immune system’s ability to function.

How is lactose digested or broken down?

Because lactose is a complex sugar, it needs to be broken down in order for your body to experience all of the benefits.

Lactase is a specific protein found in the lining of your small intestine. When you ingest anything that contains lactose — like ice cream, milk, yogurt or cream cheese — the lactase located in your small intestine breaks down the lactose you’ve consumed into two, smaller simple sugars: glucose and galactose.

“Glucose and galactose are simple sugars, so they’re easily used by the body,” explains Dr. Lee. “Glucose and galactose get absorbed and used for energy, storage and other biological processes.”

What being ‘lactose intolerant’ means in this process

You experience lactose intolerance when your body can’t produce enough lactase to break down all the lactose you’re consuming.

“The lactase activity you have is dependent on how much lactase enzyme is available,” Dr. Lee further explains. “If you consume a large quantity of lactose in a short amount of time, and more than what your supply of lactase can keep up with, you inevitably get leftover lactose that gets sent down to the rest of your digestive system intact because it didn’t get broken down.”

Remember: Lactose is a complex sugar, which means it’s hard to digest and break down. Without the lactase proteins in your small intestine, lactose moves onward to your large intestine but it can’t be absorbed. As a result, your body works to flush it out of your system.

“Think of your colon like a pipe,” illustrates Dr. Lee. “If you have lactose in your colon, your body will try and flush that out by pulling water from outside of your colon (intravascular space) into the inside of your colon (intra luminal space) to achieve equilibrium. In doing that, it pulls so much water into your colon, causing diarrhea and a lot of cramping.”

How lactose intolerance can develop

You can develop lactose intolerance in a few different ways.

Most commonly, our bodies naturally produce less and less lactase as we age, leading some to develop lactose intolerance later in life.

“Your genetics can play a role,” notes Dr. Lee. “We know, stereotypically, that people of color tend to have a higher incidence of lactose intolerance because they don’t produce as much lactase.”

Illnesses can also cause temporary lactose intolerance, particularly if you’re prescribed antibiotics for any length of time.

“Anyone with severe cellulitis, sinusitis or serious pneumonia may be prescribed heavy, broad-spectrum antibiotics. They can then develop transient lactose intolerance if the antibiotics rob them of their gut flora in that temporary time period,” she continues. “Most people recover after the antibiotic course is over, but some people don’t.”

Some may even have a higher risk of developing lactose intolerance if they have conditions that directly affect their gut health, like:

• Crohn’s disease.
• Inflammatory bowel disease (IBD).
• Scleroderma.
• Mesenteric ischemia.

“There’s a wide variability of intensity or degree of lactase deficiency,” she says. “Your symptoms tend to get worse the more lactose you consume, so there’s not an on or off switch.”

If you’re living with lactose intolerance, you’ll need to make lifestyle changes to reduce the severity of your symptoms and find milk alternatives that won’t poorly affect your gut health.

“Most people aren’t 100% lactase deficient,” clarifies Dr. Lee. “Most people still produce some lactase, but they’re such a poor lactase producer that they can only tolerate small infusions of lactose at a time.”