A 'Blue Zone' heart doctor says he recently stopped drinking milk because of his own research — but he hasn't cut back on cheese

• Dr. Gary Fraser has been examining how drinking milk impacts human health for years.
• Dairy milk is nutrient-rich, but also associated with a greater risk of prostate and breast cancers.

For decades, Dr. Gary Fraser was a cow milk drinker.

A practicing cardiologist with over 50 years of experience, Fraser lives in the longevity Blue Zone of Loma Linda, a Los Angeles suburb where Christian Seventh Day Adventists often live about a decade longer than their fellow Californians.

In addition to their religion, Adventists tend to practice regular exercise, and lacto-ovo vegetarianism, eating plenty of veggies, beans, and dairy products — but less meat — than your average American.

Fraser has been interrogating how this religion-based diet and lifestyle impacts human health, longevity, and chronic diseases for decades, studying the eating patterns of nearly 100,000 Seventh Day Adventists scattered across the US and Canada.

He discovered, for example, that nuts — an Adventist diet staple —are a more heart-healthy protein source than meat. Fraser has also found numerous other ways that Adventist diets contribute to lower rates of heart disease, high blood pressure, obesity, diabetes, and even cancer.

But not everything the Adventists do is science-backed. It wasn't until a couple years ago that Fraser — a lifelong Adventist — reconsidered his own position on drinking milk.

Milk hasn't ever been strongly associated with any major heart issues, so Fraser felt pretty good about including the calcium-rich liquid in his diet, as is traditional for Adventists.

Now, after digging into the data on prostate and breast cancer rates among Adventist milk drinkers, he says he's reversed course, and essentially eliminated cow's milk from his diet.

"It's controversial." Fraser told Insider of his most recent research. "Dairy is obviously complicated in its biological effects."

Fraser stopped drinking milk after he investigated its effects on breast and prostate cancer risk

Fraser had known for a long time that drinking milk does a body good as a major source of calcium, which we need for strong bones and healthy blood.

But Adventists get plenty of calcium from non-dairy sources. Only about 20% of their calcium comes from milk, cheese, and yogurt. The rest is a mix of beans and other legumes such as lentils, as well as tofu, almonds, seeds, and leafy greens like spinach.

Because a good portion of Adventists adhere to a vegan diet, Fraser was able to separate out data on milk drinking from healthful calcium intake, and what he found startled him.

According to several recent research studies led by Fraser, dairy milk seems to be associated with a higher risk of breast and prostate cancer.

Relatively small quantities of milk, less than three-quarters of a cup a day, made the difference. Whether the milk people drank was whole or skim didn't matter; all dairy milks increased the risk of breast cancer for women, and prostate cancer for men.

Being "a guy that likes to crunch numbers," Fraser decided he had to follow his own data and give up milk.

"I actually reckon that the best way to go is non-dairy milk," Fraser said. "You've now got some good options — oat and almond and soy and flax, and all kinds of things."

Fraser still eats cheese, a calcium-rich food that is not associated with prostate cancer

Fraser said he still enjoys some dairy, just not the milk.

"I still eat small amounts of cheese," he said.

Previous research has suggested the unique way nutrients like protein and calcium are structured in cheese doesn't have the same negative health impact as milk. Though he doesn't enjoy yogurt, Fraser says it's also a fine choice, as his data suggests that it won't raise cancer risk like milk does.

He's not exactly sure what the mechanism behind the milk-cancer connection is, but he suspects the culprit has something to do with how drinking milk impacts our hormones.

There are two leading suspects: the protein in milk, which can up the levels of insulin-like growth factor 1 (IGF-1) in our bodies, contributing to cancer risk, or the bovine hormones in the milk itself, from pregnant and lactating cows.

"The way you eat really makes a difference to your biology," he said.

Still, cancer risk is a complicated equation that involves not only what we eat, but environmental factors and our unique genetics.

Next, Fraser wants to study how milk drinking impacts human mortality. He's open to the idea that milk consumption may not have that much of an effect on early death, since most breast and prostate cancer diagnoses are survivable conditions.

"Dairy's a pretty interesting food," he said.