Few beverages are as controversial as milk. There are skim devotees, people who swear by 2 percent, and those who refuse to pour anything but whole milk over their cereal. On top of that, a sea of conflicting studies on the health impacts of dairy products adds to the confusion. Now there’s new research to consider, and it offers compelling evidence for switching to low-fat milk. The study, which was led by Brigham Young University exercise science professor Larry Tucker, found that people who consumed high-fat milk showed significantly greater biological aging than those who chose low-fat or skim milk.
“It was surprising how strong the difference was,” Tucker said in a press release. “If you’re going to drink high-fat milk, you should be aware that doing so is predictive of or related to some significant consequences.”
The study assessed health data from over 5,800 American adults (a number that’s representative of the entire U.S. population), all drawn from the National Health and Nutrition Examination Survey. The respondents answered questions about how frequently they drank milk, and what kind they chose. Almost half of those studied consumed milk daily, and another 25 percent had milk at least weekly. The majority of the group drank high-fat milk (whole milk or 2 percent), and about 27 percent chose low-fat or skim milk. Tucker also controlled for other health variables like exercise, age, smoking habits, and protein intake.
To assess biological aging among this group, he focused on telomeres, which are sections of nucleoproteins located at the ends of human chromosomes. They help protect and stabilize the chromosome, and they’re also clear markers of age: Every time a cell divides, the telomeres become slightly shorter. As a result, your telomeres slowly shrink as you age. But natural cell replication isn’t the only thing that affects them—diet and lifestyle play a role, too. Previous research shows that eating plenty of fiber, for example, correlates to longer telomeres and less biological aging.
In this study, Tucker found that milk fat also has a strong correlation to telomere length. Specifically, the data showed that adults who consumed whole milk had significantly shorter telomeres than those who drank skim milk. In addition, for every 1 percent increase in milk fat (2 percent versus one percent milk, for example), telomeres were 69 base pairs shorter. That translates to over four years of additional biological aging depending on which carton study subjects chose at the grocery store.
The correlation held up across adults who reported drinking milk daily or weekly and even when Tucker adjusted for differences in demographics, lifestyle, and diet. Interestingly, the correlation didn’t appear among those who rarely drank milk, and people who never drank milk actually had shorter telomeres than those who chose low-fat milk (so think twice before you skip dairy altogether). For everyone who did include milk in their diet, however, the association was clear.
“The more milk fat subjects consumed, the shorter their telomeres tended to be,” Tucker wrote in the study.
The correlation is compelling, but Tucker cautioned that the study isn’t designed to show causation, so it’s not certain that milk preferences are behind the changes in telomeres. He hypothesized that saturated fat, a large component of milk fat, might partially explain the link between milk and biological aging. Adults who had elevated levels of saturated fat in their diets showed a strong correlation between telomere length and milk fat intake.
Regardless of the cause, the dramatic shrinking in telomeres is something to take seriously. According to the study, adults who have shortened telomeres also have higher rates of chronic diseases like obesity, cancer, depression, and heart disease. They also tend to have shorter lifespans than average. Tucker noted that the findings support current dietary guidelines, which encourage low-fat milk over 2 percent and whole milk.
“It’s not a bad thing to drink milk,” Tucker said. “You should just be more aware of what type of milk you are drinking.”
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