Many adults struggle with lactose intolerance and do their best to avoid dairy. There are a lot of misconceptions, however, about the biology behind it and which dairy products are the best and worst. I've compiled some basic information here to hopefully clear up the fundamentals:
What is lactose, and why are some people intolerant?
Lactose is a type of sugar most commonly found in milk and other dairy products. In the body, lactose is usually broken down into two simple sugars -- glucose and galactose -- by an enzyme called lactase. People are lactose intolerant when their bodies don't make enough lactase. Without lactase, the lactose can't be properly digested and causes what I politely term "gastrointestinal distress" (a.k.a. gas and bloating). Lactose intolerance usually runs in families, but it can also happen out of the blue. Some people are more intolerant than others; it totally depends on how much lactase your body is able to make. People with a mild intolerance make enough lactase to digest most, but not all lactose, and people with a severe intolerance make little or no lactase at all. That's why some people can have a little milk and be ok, but others have to avoid it completely.
Why do some foods cause more "distress" than others?
If you are only moderately lactose intolerant, you may notice that you can have aged cheeses but not milk. That's because cheese (even young cheese) has less lactose than fluid milk. In the cheese-making process, curds are separated from whey, which is drained away and used for various other food applications. The whey is where the majority of the lactose ends up, so cheese is sort of a lactose-reduced version of milk. To boot, as cheeses age the lactose they do contain continually breaks down, introducing some of the complex and yummy flavors of aged cheese while also making it easier to digest! If your intolerance is only mild or moderate, and you love cheese and miss it, you might have luck trying well-aged cheeses.
Yogurt with "live and active cultures" (meaning live bacteria) can also be ok for people with mild or moderate lactose intolerance. The bacteria that turns milk into yogurt also breaks down lactose into smaller, more digestible sugars. Check the label on your yogurt for "live and active cultures." That means most of the lactose-digesting work has been done for you! Just don't assume all yogurt is okay; if it doesn't contain live cultures, you're taking a gamble. Frozen yogurt is a great example -- it usually doesn't contain live cultures anymore, and to boot, whey and other dairy products are often added for texture and flavor, introducing lots of new lactose to the mix with no way to break it down. It's difficult to stay completely away from lactose. Sometimes you end up eating dairy without realizing it (not uncommon when dining out) or sometimes the frozen yogurt or ice cream your friends are all ordering is just too tempting to resist. Which brings me to my next topic.
Do pills really help?
You may have noticed there are products out there meant to help you be able to eat more milk and ice cream. You can buy pills, powders or drops over the counter that you're supposed to take with dairy. How do these work? These are simply lactase supplements -- they contain the enzyme you lack! They work because the enzymes in the pill work to break down the lactose you eat, which allows it to pass through your system without any problems. Lactose-free milk is another product you may have noticed at the store. This is just regular cow's milk that has been treated with the same lactase enzyme that's missing in your body. This means that all of the lactose that was originally present in milk is now in its simplified form -- glucose and galactose -- which are easy to digest! You may notice, however, that lactose-free milk tastes sweeter than regular milk. That's because the lactose in the milk has been broken down into glucose and galactose, both of which happen to taste significantly sweeter than lactose. But don't worry, despite the increased sweetness, the total grams of sugar remain the same and so do the calories. So sit back and enjoy the sweeter side of lactose intolerance!