The news about drinking milk to stay healthy and live longer is sometimes contradictory and often confusing. Some people believe that they should drink three glasses of milk a day, while others think that they should not eat any dairy or drink any milk at all. What are the facts?
Milk is often called a whole food because it provides a lot of important nutrients, including those that keep our bones strong and healthy. Milk is rich in calcium; one glass of milk helps us meet about 30% of our daily calcium needs. To increase our body’s ability to absorb calcium, we need vitamin D. Our bodies can make vitamin D from the sun, but for some people, such as those who live in areas with limited sunlight or those who have darker skin color, it is hard to get enough vitamin D from only the sun. Another way to get vitamin D is through our diet, and fortified milk is a good source of dietary vitamin D. Besides calcium and vitamin D, we can get magnesium, potassium, and protein from drinking milk. All these nutrients strengthen our bones. Stronger bones can decrease the chance of bone fracture after a fall and decrease the risk of having osteoporosis or other bone diseases. These problems are common concerns as we become older.
In the United States, milk is described based on the amount of fat the milk has: whole milk, reduced fat milk (2%), low-fat milk (1%), and skim milk (fat free). There are several common misunderstandings about these names. People often think that the percentage means the percent of fat you get when you drink the milk; for example, that drinking one glass of reduced fat milk helps them meet 2% of the daily need. This is not true. The percentage is the amount of fat found in the milk relative to its total weight. One glass of milk is usually 250 grams. So, one glass of 2% milk provides 5 grams of fat (8% of our daily need), and one glass of 1% milk provides 2.5 grams of fat (4% of our daily need). The names “whole milk” and “fat free milk” are also confusing. Some people think that whole milk is made with 100% fat, and fat free milk is made with nothing but 100% water. Again, this is not the case. One glass of whole milk provides about 8 grams of fat, which is about 3.25% fat, but this can be as high as 3.5% depending on the milk source. That’s why whole milk is also called 3.25% or 3.5% milk.
The amount of fat in the milk also changes the number of calories provided by the milk. Whole milk provides the most calories, followed by reduced fat milk, low fat milk, and skim milk. Other than the different amounts of fat and calories, all milks (including skim) have the same amount of nutrients. So, if our goal is to decrease the number of calories and fat from our diet but still get all the nutritional benefits from drinking whole milk, these other types of milk are good alternatives.
This is all good news and there are a lot of choices. So, why does milk sometimes have a bad reputation? Because there have been studies published with headlines like: “3 Servings of Milk a Day Linked to Higher Mortality in Women.” However, when relying on news reports to make decisions about our diet, it is important to understand the circumstances of the study it’s based on.
In this case, the study was done in Sweden, which is in northern Europe. As mentioned, one nutrient important for bone health is vitamin D. We can get vitamin D from the sun and from food, such as fortified milk. However, the authors of the study did not mention whether the study participants have enough sunlight exposure for making vitamin D. They also did not report if the participants drink any milk fortified with vitamin D. We also don’t know if the participants have genetic differences that make them metabolize vitamin D differently and have different vitamin D needs. It’s possible that these study participants are vitamin D deficient, and so their bodies are not good at absorbing calcium, and thus they have higher hip fracture and resulting mortality. But, we don’t know for sure. It is also important to remember that the reported harmful effects are seen only in participants who drink three or more glasses of milk, not those who drink one or two glasses of milk. Also, the researchers did not study adults younger than 40 years old or young children, so we can’t say anything about whether drinking milk will cause any harm in these people.
This example illustrates well that when there are so many questions still unanswered, there is not enough clear evidence for completely eliminating (or adding) a specific food or type of food. Taking a close look at this study reveals that it isn’t enough to make a solid conclusion that drinking milk might be harmful.
Some people avoid drinking milk because they experience bloating, gas, nausea or diarrhea after drinking milk. These problems happen because of lactose, a sugar naturally found in milk. People who cannot break down lactose are lactose intolerant. Genetics play a big role in affecting the severity of the lactose intolerance. To break down lactose, we need an enzyme called lactase. For each of us, our ability to make this enzyme varies because of genetic differences in the lactase gene. Some of us can make lots of lactase and have no problems drinking milk or eating foods containing lactose. But for some of us, our genetics change how efficiently our body can make lactase, so we can’t tolerate these foods as well. Some of us can still make some, but not a lot of, lactase, and so we can still eat a small amount of foods that don’t have lots of lactose, such as cheddar, Swiss, and other hard cheeses, or probiotic yogurts that have live “good bacteria.” A few of us just can’t make any lactase, and need to eliminate foods containing lactose and eat only lactose-free foods or use lactase supplements. Other factors like age and health conditions also affect how much lactase our body makes and the severity of the lactose intolerance.
The evidence, then, shows that drinking milk and eating dairy can be highly beneficial in some people, but may be problematic in others, and so there is no one answer that addresses everyone. This is the core of our research at the UNC Nutrition Research Institute – learning how Precision Nutrition works based on individuality in genes, metabolism, and environment.
None of this information is intended to be a substitute for professional advice, diagnosis, or treatment. Always seek the advice of your doctor or other health professionals if you have any questions regarding a specific medical condition.
For a delicious way to incorporate healthy fats in your diet, try making this delicious Asparagus Quiche.
Cecilia Kwan, PhD, RD
Postdoctoral Research Associate, Smith Lab, UNC NRI