If a glass of milk or a scoop of ice cream wreaks havoc on your stomach, you're likely dealing with lactose intolerance, a condition marked by the inability to fully digest lactose (a naturally occurring sugar in milk and dairy products).
While an upset stomach after eating dairy can signal lactose intolerance, every person's symptom picture is unique. Some people may have certain symptoms and not others, and these symptoms might also fluctuate depending on the foods eaten and how much lactose they contain, Rabia A. De Latour, MD, a gastroenterologist at NYU Langone Health in New York City, tells LIVESTRONG.com.
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Here, Dr. De Latour explains the common symptoms you might experience if you're dealing with lactose intolerance, plus ways to diagnose and manage the condition.
What Causes Lactose Intolerance?
Lactose intolerance is caused by a deficiency of lactase, an enzyme produced by the small intestine that breaks down lactose, per the Cleveland Clinic.
While you can be born with lactose intolerance (known as congenital lactase deficiency), this genetic disorder is quite rare, according to the U.S. National Library of Medicine (NLM).
Rather, most people develop lactose intolerance later on: People often begin to drink less milk after childhood, so the amount of lactase they produce decreases, per the Mayo Clinic.
In fact, it’s quite common for people to make less lactase as they age. Approximately 65 percent of people worldwide have issues digesting lactose in adulthood, per the NLM.
Other factors — including illness or injury in the small intestine — can affect lactase production and result in lactose intolerance, according to the Mayo Clinic. For example, certain digestive diseases (such as Crohn’s disease, ulcerative colitis and celiac disease) or intestinal infections can reduce the amount of lactase your body is able to make.
1. Diarrhea
Loose stool after eating dairy is a telltale sign of lactose intolerance.
Here's why: Because the lactase enzyme is lacking, lactose can't be broken down. As a result, the undigested lactose in the bowel will draw water into the colon and cause diarrhea, Dr. De Latour says.
2. Nausea, Stomach Cramping and Bloating
When you can't digest lactose, it ends up in the colon where colonic bacteria can break it down. This process causes gas, which can lead to bloating, cramps and pain, Dr. De Latour says.
What's more, bloating and distention can lead to nausea and vomiting, she adds.
3. Constipation
While constipation is a less common sign of lactose intolerance, technically speaking, it can happen, Dr. De Latour says.
"As bacteria in the colon break down the undigested lactose, it produces methane gas, which can slow the gut down," Dr. De Latour explains. "Slowing the gut down allows the colon to extract more water from stool, and this can cause constipation."
How Long Do Lactose Intolerance Symptoms Last?
“If you eat lactose with an intolerance, the symptoms of discomfort can last anywhere from 30 minutes to two days while the food passes through your system,” Dr. De Latour says. “However, most of the time symptoms resolve within a few hours.”
What to Do if You Think You're Lactose Intolerant
For starters, keep track of which dairy products you eat and when you experience stomach discomfort or digestive issues. Based on that, try eliminating these foods from your diet for a few days to see if your symptoms improve, according to the Mayo Clinic.
But, for a definitive diagnosis, you should see a doctor who can perform tests to assess your lactose intolerance.
One such test, the hydrogen breath test, calculates the amount of hydrogen in your breath after drinking a lactose-rich beverage, per the Mayo Clinic. Too much hydrogen shows that you're not properly digesting and absorbing lactose.
There's also a blood test that determines the quantity of glucose in your bloodstream after sipping a lactose-based drink. In this case, if your glucose level doesn't increase, it indicates that your body isn't digesting and absorbing lactose, according to the Mayo Clinic.
Tip
Any time you're struggling with stomach-related symptoms that cause discomfort, you should seek medical help, Dr. De Latour says. And always see a doctor if you have any red flag signs such as unintended weight loss or bloody stool, especially if you have a family history of bowel issues, she says.
How Is Lactose Intolerance Treated?
While lactose intolerance can't be cured, you can manage your symptoms or even be symptom-free by controlling your diet and monitoring your lactose intake, Dr. De Latour says.
Here are a few tips for coping with lactose intolerance from the Cleveland Clinic:
1. Experiment With Different Dairy Products
Most people preserve a certain level of lactase activity and can have some lactose without symptoms. Through trial and error, you can discover which dairy products you can tolerate. Some foods contain less lactose, such as hard cheeses, and may produce little or no GI distress.
High-Lactose Foods
The following foods are considered high-lactose products as they possess approximately 5 to 8 grams of lactose, per the Cleveland Clinic:
- 1/2 cup of milk (whole, reduced fat, fat-free, buttermilk, goat's milk)
- 1/4 cup of evaporated milk
- 2 oz. of cheese spread and soft cheeses
- 3/4 cup of cottage cheese
- 3/4 cup of ricotta cheese
- 1/2 cup of yogurt, plain
- 3/4 cup of ice cream
- 1/2 cup of heavy cream
- 2 tbsp. of nonfat dry milk powder
2. Opt for Smaller Servings of Dairy
A smaller portion is less likely to upset your stomach.
3. Have Dairy With Meals
You might tolerate lactose better — and have fewer symptoms — when you eat it with other foods.
4. Try Lactose-Reduced or Lactose-Free Products
You can often find these products in the dairy section of your supermarket.
5. Use Lactase Enzyme Tablets or Drops
Supplementing with lactase enzyme — available in over-the-counter products like Lactaid — may help you digest lactose-containing foods and decrease stomach discomfort.
What About Calcium?
If you're limiting lactose-rich foods, you might be concerned about getting enough calcium because milk and dairy are rich sources of the mineral, which is essential for bone health.
Luckily, you can still get the calcium you need to maintain a balanced diet through other food sources. Nondairy foods high in calcium include:
- Sardines
- Kale and collard greens
- Broccoli rabe
- Beans
- Firm tofu
- Calcium-fortified orange juice, soy milk and almond milk
If need be, you can also consult with your doctor or a registered dietitian about taking a calcium supplement.
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Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.