It's more and more common to hear runners say they've decided to cut milk out of their diet because they find it hard to digest, they're intolerant, or it makes them feel heavier when they train or race. Years ago, nobody would have considered a balanced diet without milk, but lactose is increasingly being labeled “hard to digest,” especially in running.
But before we get into the controversy, let's get to know this food and what's in it a little better.
Milk is mostly water (80%) and contains small amounts of carbohydrates (4g/100g), protein (3g/100) and fat (3g/100 in whole milk). Since it's basically water, its calorie content isn't very high (65Kcal/100g).
At first glance, this composition would be similar to that of other foods we eat that, however, aren't caught up in this controversy. But if we take one small step further and look more closely, we'll understand why there's so much debate.
Milk contains a type of carbohydrate called lactose. This kind of sugar isn't common in our diet (only milk, and to a lesser extent dairy products, contain it). That's why the enzyme that digests it in the gut (lactase) doesn't work the same way in every runner. In fact, the body makes this enzyme according to its needs: people who drink a lot of milk will have more of it, and vice versa. And here's a curious effect: people who used to drink milk and decide to stop will also end up with less lactase, because the body doesn't need it. As a result, lactose isn't digested well by people who have little of the enzyme, and this can lead to stomach problems, diarrhea and even damage to the intestinal lining and poor absorption of other nutrients. However, if we digest milk properly, that means we don't have any lactase deficiency.
Other drawbacks have to do with allergies, residues of medication and hormones, increased mucus production and respiratory problems. Although we could make the list longer, there aren't enough scientific studies to back these points up.
Milk is our main source of calcium and vitamin D. We all know calcium is essential for good bone mass (something especially important for women and runners), but it's absorbed better with vitamin D alongside it, and milk is an excellent vehicle for that. In fact, one of the hottest topics in nutrition right now is the role of vitamin D in many different functions, and the lack of this vitamin in most of the population. With an adequate intake of milk, we meet the recommendations for vitamin D; without it, we'd struggle to get there from other foods.
Another strong point is its protein profile: high biological value protein that gives us all the amino acids we need (most protein supplements are made from whey protein). What's more, these proteins mostly belong to the albumin family, which has been shown to have anti-inflammatory and anti-cancer effects in animal studies.
If we go by the studies, there isn't enough evidence to say we should limit how much milk we drink, while there is consensus on the benefits of the nutrients it contains. As a nutritionist, I believe there are no good or bad foods in absolute terms; instead, we should focus on eating a balanced, varied diet tailored to each person. If there really is an intolerance, we'll cut out the food that causes it, but first it's important to see a specialist to pin down exactly which component is behind the intolerance and confirm which other foods it can be found in.
As a runner, if you notice some discomfort or heaviness after drinking milk (but nothing more serious), avoid having it before a race or workout, and try fitting it in at another time of day or on rest days. If you still feel uncomfortable, don't hesitate to see a specialist to rule out allergies and intolerances, and to make sure you're eating a rich, balanced diet that keeps your energy up so you can run with confidence.