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One Major Side Effect of Eating Dairy, Says Science

Like almost any food, too much milk (and other dairy) might not do a body good.
FACT CHECKED BY Kiersten Hickman

If you're lactose intolerant, you don't need us to tell you what eating dairy can do to your belly. You've been there and felt that. But for those who aren't sensitive to lactose we'll fill you in: The inability to produce lactase, the enzyme that helps the gut break down milk sugar (lactose), often causes cramping that can double you over, awful gas and bloating, and diarrhea. Sounds great, no? A quarter of all Americans experience this one major side effect of eating dairy.

The rest of us who tolerate dairy products just fine may be interested in knowing about other potential side effects of consuming a lot of dairy—particularly whole milk: increased risk of certain cancers, maybe a cardiovascular disease, and type 2 diabetes, according to scientific studies.

Before you dump out the milk and ice cream in your house, however, keep in mind that the vast majority of the studies linking milk and disease are what's known as "observational studies," meaning they look for an association between diet and your likelihood of getting a disease. They don't claim to prove that eating a certain food will cause the disease. Still, this research offers a glimpse at how the foods we eat (and how much of them we consume) may affect our bodies, because our diet is arguably one of the most powerful health influences that we can control.

Here's a look at some of the research suggesting potential side effects of dairy consumption that may make you rethink how much milk you drink, and for even more healthy eating tips, be sure to check out our list of The 7 Healthiest Foods to Eat Right Now.

Type 2 diabetes and aging

Dairy products

Cell growth just doesn't happen in response to nutrients—like water and fertilizer on a vegetable seed. Scientists have discovered it's a highly regulated process controlled by multiprotein complexes. One of those master switches for cell growth is called mTORC1 (for mammalian Target Of Rapamycin Complex 1), a nutrient-driven regulator of growth that plays a key role in physiology and metabolism.

A 2021 review in the journal Biomolecules presented a number of epidemiological studies showing an association between long-term consumption of cow's milk and overactivation of mTORC1, which causes signaling cascades involved in everything from acne, type 2 diabetes, and cancer to aging.

Other studies, however, have shown that intake of dairy products is associated with a lower risk of type 2 diabetes. A large meta-analysis of dairy consumption in more than 150,000 people by researchers at the Harvard School of Public Health, for example, found no link to type 2 diabetes but a reduced risk associated with eating more yogurt.

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Prostate cancer

plate of many cheese on a cutting board

Consuming a lot of dairy products, including whole and low-fat milk and cheese, was found to increase the risk of prostate cancer, according to a 2015 analysis of studies in the American Journal of Clinical Nutrition.

Other research using 28 years of data from 21,660 participants in the Physicians Health Study, found that men who ate two and a half servings of dairy daily were at a 12% increased risk of prostate cancer when compared with men who had less than the equivalent of four ounces of milk or an ounce of cheese daily.

But more recent research, a 2019 study in Nutrients, calls those previous findings into question. This analysis of 11 years' worth of data on 40,472 men, 4,134 of whom were diagnosed with prostate cancer, showed no significant association with prostate cancer. The median daily intake of dairy was about a cup of milk.

Here's What Happens to Your Body When You Drink Milk.

Overall mortality

drinking milk

A 2017 study by Swedish epidemiologists in American Journal of Epidemiology showed a connection between high milk consumption and higher mortality rates in men and women. The study looked at dietary data on more than 100,000 people and found that those who consumed the most amount of milk—at least three glasses a day—and ate the least amount of fruit and vegetables (about one serving daily), had three times the greater risk of prematurely dying from all causes when compared to people who drank no more than a glass of milk a day and ate the most fruits and vegetables. The researchers hypothesized that the antioxidant-rich fruits and vegetables may have reduced low-grade inflammation and oxidative stress that milk consumption is believed to trigger.

Here are 14 Tips to Reduce Inflammation to Lose Weight Faster, According to RDs.

Cardiovascular disease

pour nut milk alternative into smoothie in a blender

A cup of whole milk contains 4.6 grams of saturated fat. The American Heart Association recommends opting for low-fat milk over whole milk because of the longtime connection between saturated fat and high cholesterol and increased risk of heart disease. But recent research suggests that saturated fats may not be as harmful as once thought and some studies have failed to find a clear link between consuming full-fat dairy products and poor heart health. In fact, an analysis of 20 studies presented at the 2018 Congress of the European Society of Cardiology found a connection to a higher risk of cardiovascular disease only in people who consumed a lot of milk, upwards of a liter a day.

Writing in the New England Journal of Medicine in 2020, renowned Harvard Medical School professors Walter C. Willett, MD, Dr.PH and David S. Ludwig, MD, PhD, note that dairy consumption has not been definitively linked to risks of cardiovascular disease or diabetes. Dairy will likely increase the risk of certain cancers (possibly prostate and endometrial cancers) while reducing the risk of colorectal cancer, but Willett and Ludwig caution that the health impact of consuming dairy foods depends strongly on what foods they are being compared to. For example, a diet full of refined grains, starches, sugar, and meat may be worse for your heart than drinking a glass of milk every day.

But there's another major side effect of eating dairy that should be of concern, Willett notes in an interview with Medical News Today—the impact on the environment due to greenhouse gas production. "If everyone consumed 3 glasses (of milk) per day, this would make avoiding extreme global warming very difficult," Willett said. "This should at least be considered when making decisions about production and consumption of milk."

Done with dairy? Try these 22 Genius Tips to Cut Back, According to Experts.

Jeff Csatari
Jeff Csatari, a contributing writer for Eat This, Not That!, is responsible for editing Galvanized Media books and magazines and for advising journalism students through the Zinczenko New Media Center at Moravian University in Bethlehem, PA. Read more about Jeff
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