Lactose intolerance, the inability to break down lactose — the natural sugars found in milk and milk products — is extremely common. Approximately 30 million American adults have some degree of lactose intolerance by age 20, according to the U.S. National Library of Medicine.

Humans cannot digest lactose without the help of an enzyme called lactase. If your digestive system produces and maintains sufficient levels of lactase, which splits lactose into the much-more-absorbable sugars glucose and galactose, you should be able to tolerate milk products. 

But most people across the globe, as well as a large portion of the U.S. population, are deficient in lactase. Genetics play a huge role in determining whose bodies do and do not produce enough of this enzyme. Lactase deficiency is far more prevalent among certain ethnic groups, especially people of Native American, African-American, Asian, Mediterranean and Jewish descent. 

Genetics aside, anyone’s body can lose the ability to maintain adequate lactase levels as they age. It’s also common to stop producing the enzyme temporarily following a bout of infectious gastroenteritis. And if you take a lot of NSAID painkillers like ibuprofen or aspirin, or if you injure your small bowel in any way, your lactase levels will likely be lower.

Symptoms of Lactose Intolerance

If your body can’t digest lactose-containing dairy products, you can experience unpleasant side effects, including abdominal pain, bloating, cramps, flatulence, nausea and diarrhea. These symptoms normally start within 30 minutes to two hours after consuming lactose. If you take down a large amount of dairy at once, your woes will probably be much worse.

But ironically, if your dairy binge consists of a lot of fat — such as a bean-and-cheese burrito smothered in guacamole — your symptoms may not be as bad. If you usually follow a dairy-free diet but cheat with a high-fat meal, it can be healing. Fat leaves the stomach twice as slowly as the sugars, so you’re not putting a bunch of lactose in the small bowel at one time.

How to Know You're Truly Intolerant

First off, know that lactose intolerance is not the same thing as a milk allergy, which is quite rare, especially among adults. More often, it’s babies and small children who are allergic, but even they often outgrow milk allergies over time. The symptoms of a milk allergy are also different from those of lactose intolerance. Rather than bloating or tummy upset, little ones who are allergic to milk get really sick.. Milk kicks their immune system into overdrive, and they may develop a rash, hives, swelling or, in severe cases, struggle to breathe. 

If your symptoms (general bloating, diarrhea) indicate intolerance, there’s a simple and fairly reliable way to determine whether you’re lactose intolerant. Just eliminate milk products from your diet for two weeks to see if your symptoms subside. Download a three-day, dairy-free meal plan to get started.

But if you’re still not sure — or if you want extra assurance before banning your beloved lattes — ask your doctor to perform a diagnostic test to prove you’re lactose intolerance. The most common is the hydrogen breath test, which measures the amount of this gas in your breath. Normally, there is very little. But if you give someone who’s lactose intolerant a bunch of lactose, it will get broken down by bacterial fermentation in your colon, which will generate hydrogen. This is why you get gas and diarrhea. But in the process, you’ll also exhale enough hydrogen to make it clear that you’re lactose intolerant. 

Your doctor can also recommend a lactose tolerance blood test. Since the body creates glucose when it breaks down lactose, this test looks for changes in glucose levels in your blood before and after you’ve consumed lactose. If the amount of glucose doesn’t rise to a certain level after drinking a lactose solution, that signals an intolerance. But before getting either of these tests, Dr. Auld strongly advises trying the dairy-elimination route because it will likely give you the answers you need.

Treating Lactose Intolerance

There is no known method of preventing or curing lactose intolerance. The severity of your lactase deficiency will determine which products or strategies work best for your body. You may be able to consume small amounts of milk or tolerate lower-lactose milk products, such as hard cheeses and yogurt with live cultures. 

Or, you may need to avoid dairy altogether and choose lactose-free milk products, such as Lactaid, or other dairy-like products made from soy, almonds, rice or coconuts. Over-the-counter lactase pills can also help. Also available as liquid drops, these may make lactose-containing foods more tolerable. 

Keep in mind, milk products hide in a surprising number of food products. Packaged snack foods, chocolates, cakes, creamy sauces, salad dressings, salami, and boxed soups and potatoes often contain dairy. Make sure to study any packaged food’s ingredient list for lactose code words, including milk, lactose, whey, curds, milk by-products, dry milk solids and nonfat dry milk powder.

Getting Enough Nutrients

Milk and milk products are a major source of calcium, crucial for bone health and building strong teeth. So when you limit or completely ditch dairy products, you run the risk of inadequate calcium intake. Over time, this can contribute to osteoporosis — weak, brittle bones that fracture easily. 

If you’re dairy-free, load up on calcium-rich foods, such as leafy greens, broccoli, okra, oranges, almonds, canned salmon, sardines, soy products and legumes. Yet it still can be tough to get enough calcium from these foods alone, he says, so consider taking calcium supplements — especially if you’re a woman who is pregnant or nursing. Calcium requirements vary by age, gender and other factors, so talk with your doctor about how much of the mineral you should shoot for each day. 

And don’t forget about vitamin D. If you follow a low- or no-dairy diet, you’re going to have a problem with low vitamin D levels. Very few foods contain sufficient vitamin D; you’d need to eat a whole lot of leafy greens.

But even if you do dairy, the best source of vitamin D is sunlight exposure. In San Francisco, vitamin D deficiency is the rule rather than exception. So just as with calcium, if you’re lactose intolerant, definitely consider vitamin D supplements.