Humans are unusual among mammals: many of us keep drinking milk long after infancy. For most of the world's adults, though, the body is not built for it. Here is what lactose intolerance is, how common it really is, what dairy may mean for your gut, and how to eat comfortably if milk does not agree with you.
What is lactose intolerance?
Lactose is the natural sugar in milk. To digest it, your body needs lactase, an enzyme produced by cells in the lining of the small intestine. Babies make plenty of it. In most people, though, lactase production gradually falls after infancy, a pattern called lactase nonpersistence.
Without enough lactase, lactose travels undigested to the colon, where bacteria ferment it. That can cause abdominal pain, bloating, flatulence, nausea and diarrhea, beginning 30 minutes to 2 hours after eating dairy.
How common is lactose intolerance?
Society often sees lactose intolerance as unusual, but it is the norm. A global meta-analysis covering 89 countries estimated that 68% of the world's population has lactose malabsorption, ranging from 28% in western, southern and northern Europe to 70% in the Middle East. MedlinePlus puts it at approximately 65 percent of people, with lactase nonpersistence affecting 70 to 100 percent of people of East Asian descent and only about 5 percent of people of Northern European descent.
In other words, the ability to digest milk as an adult, lactase persistence, is the exception worldwide.
Do you have to give up dairy completely?
Not necessarily. Most people with lactose intolerance can have some lactose without getting symptoms, and research suggests many could have about 12 grams, the amount in roughly 1 cup of milk, with no or only mild symptoms. Yogurt and hard cheeses such as cheddar and Swiss are lower in lactose, because fermentation breaks down much of the lactose in milk.
If you suspect lactose intolerance, talk to your doctor before cutting out food groups. Symptoms can overlap with other conditions, and if you reduce dairy you will want to make sure you still get enough calcium and vitamin D.
Can dairy fat affect your gut bacteria?
Lactose is not the only part of dairy researchers are studying. In a much-discussed mouse study, a diet high in milk-derived saturated fat promoted the growth of a sulfur-loving bacterium, Bilophila wadsworthia, and increased colitis in genetically susceptible mice, through changes to bile acids. Normal mice did not develop colitis.
This is an interesting clue about how diet shapes the microbiome, not proof that dairy causes bowel disease in people. It is one more reason to favor a varied, plant-rich diet. Our article on three keys to a healthy microbiome has practical steps.
Can probiotics help with lactose intolerance?
Possibly. Many probiotic bacteria produce their own lactase-like enzymes. A systematic review of 15 randomized double-blind studies found varying degrees of efficacy but an overall positive relationship between probiotics and lactose intolerance. A daily probiotic such as Trust Your Gut Probiotic + Prebiotic Daily Essential, with 16 billion CFU of dairy-free probiotics and organic prebiotics, is one way to support your digestion. Read more about how digestive enzymes and probiotics work together.
What about protein powders?
Whey protein comes from milk, and whey protein concentrate in particular still contains some lactose, which is why it does not sit well with everyone. Our articles on whey protein concentrate and whether whey is bad for you explain the differences. If you would rather skip dairy altogether, So Lean & So Clean provides 23 grams of organic, vegan protein from pea and rice, with no added sugar.
