It sometimes feels like you need a college degree in nutrition just to go shopping.

The government has all set sorts of rules and regulations governing what manufacturers can and can’t put on food labels, in legislation like the Fair Packaging and Labeling Act of 1967 and the Nutrition Labeling and Education Act of 1990.

And the FDA regularly takes action against companies making incorrect branding claims, as it did in 2009 when Kellogg’s was forced to stop claiming that Frosted Mini-Wheats improved childrens’ inattentiveness by nearly 20 percent.

Then why are food labels still so confusing?

• In some cases, companies continue to make misleading claims.
• In some cases, government guidelines are less strict than they’d appear to be. For example, “light” or “lite” only means that a product has 33% fewer calories or 50% less fat than a “reference” food. If the reference food is loaded with calories, though, that means that the “light” version isn’t necessarily healthy. (And yes, there are rules about using the word “healthy,” too.)
• In some cases, terms are so confusing that no one could reasonably understand the difference.

Let’s unpack one set of products in that last category.

Are there any differences between “lactose-free” and “dairy-free” foods? And if there are, do they really matter?

Yes, there are important differences. And yes, they definitely matter.

The short answer to our question is that lactose-free products are still dairy foods. Dairy-free products, needless to say, are not dairy foods.

Let’s find out why the differences really are important.

Cow’s milk contains a number of ingredients. The most important are water, fat, minerals, milk proteins (mostly casein and whey protein) and lactose (sometimes called milk sugar). 

As we all know, milk is a dairy product, but it’s far from the only one. Dairy products are considered to be any food made from the milk of mammals; that means that yogurt, goat cheese and gelato are dairy products as well. (Goats are mammals, so goat’s milk is also considered to be dairy.)

That means dairy products naturally contain both lactose and casein. Those are the two ingredients we’re concerned with, when determining if a product is dairy, non-dairy, lactose-free, or dairy-free.

Put simply, lactose is the sugar that’s naturally contained in milk. It’s known as a disaccharide, which means that it’s a chemical compound composed of two single sugars, galactose and glucose. In order for lactose to be used by the body once it’s been consumed, the glucose and galactose must first be separated in the intestine. After that, the two sugars are each absorbed and can be used.

There’s an enzyme responsible for splitting lactose molecules. It’s called lactase, and it sits in the small intestine waiting for glucose to arrive. If the body doesn’t have enough lactase, though, the lactose can’t be separated and absorbed. Instead, it moves to the colon where bacteria break it down into hydrogen, methane, carbon dioxide and fatty acids – which can cause symptoms ranging from abdominal pain and bloating, to diarrhea and flatulence.

Many readers have certainly guessed the final chapter of this story by now, since those are all symptoms familiar to those who suffer with lactose intolerance. 

So, in simple terms, lactose intolerance isn’t an allergic reaction. It means that a person doesn’t have enough of the enzyme lactase to break down the lactose naturally present in milk, so they experience often-painful and embarrassing symptoms when they consume dairy products.

(There are some who actually do have a milk allergy, but that’s completely different than lactose intolerance. Those people have a food allergy, triggered by either the casein or whey proteins in milk and milk products. A dairy allergy produces different symptoms, as the immune system thinks the milk protein is invading the body; reactions can include hives, vomiting, bloody stools, and in rare cases, anaphylactic shock.)

What causes a lactase deficiency in the body? Most of the time, it’s inherited and rears its head after a child isn’t constantly breastfeeding or drinking milk from a bottle; that condition is known as primary lactase deficiency. Rarer “secondary lactose deficiency” can be caused by diseases of the digestive system like ulcerative colitis, celiac disease, gastroenteritis and Crohn’s disease, lengthy courses of antibiotics, or chemotherapy. Even rarer “congenital lactase deficiency” is a genetic condition as well.