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Is It Time to Bring Back Full-Fat Dairy?

There’s growing evidence that whole fat dairy products may be better for our health than low-fat versions. Dr. Mario Kratz is conducting a trial at the ITHS Clinical Research Center to learn how dairy fat affects our metabolic health.

Is It Time to Bring Back Full-Fat Dairy?

For decades, public health officials have recommended low-fat or nonfat dairy products over full-fat products, warning that calories and saturated fatty acids in dairy fat can attribute to obesity, diabetes, and cardiovascular disease. It seems like common sense–cut the calories and extra fat while keeping the good stuff like calcium and nutrients.

But a growing body of research has experts questioning those recommendations.

Dr. Mario Kratz, a researcher in the Public Health Sciences Division at Fred Hutchinson Cancer Research Center, is one of them. To learn more about the effects of dairy fat, Kratz is conducting a randomized clinical trial in the Institute of Translational Health Sciences’ Clinical Research Center that studies how a 12-week dietary regimen of 3 servings per day of low-fat or full-fat dairy products will impact participants’ metabolic health, compared to a control group consuming very little dairy products. The trial was informed by inferences drawn from two papers authored by Kratz and his team.

Full-Fat Consumers Had Lower Risk of Diabetes, Weight Gain

Kratz began questioning the low-fat and nonfat dairy recommendations after conducting a review of observational studies on the relationship between high-fat dairy consumption and obesity and cardiovascular and metabolic disease.

He and his colleagues came to a surprising conclusion: people who consumed high-fat dairy were no more likely to become obese than those who consumed low- or no-fat dairy. Those who ate more full-fat dairy actually had less weight gain over time and a lower risk of obesity than those who barely ate full-fat dairy products, an association that was not seen for low-fat dairy products.

For years, the general principle behind weight loss has centered on consuming less fat and fewer calories. But that principle ignores the reason why we eat in the first place—hunger. Kratz argues that fatty acids in full-fat dairy may help you feel full sooner and for longer, meaning you might skip that second bowl of cereal.

He and his colleagues came to a surprising conclusion: people who consumed high-fat dairy were no more likely to become obese than those who consumed low- or no-fat dairy.

One possible reason for the observed inverse relationship, Kratz cautioned, is “reverse causation.” People who are already obese or prone to weight gain may avoid foods high in calories and fat, while active people choose full-fat dairy. This concern is just one example for the many limitations of observational studies. “We can never know whether any association found in an observational study is reflective of a causal effect,” Kratz said.

Another understudied and possibly highly relevant property of dairy fat is that it is the most complex fat humans eat. Some of these fatty acids may have specific effects in our bodies, Kratz added, similar to hormones. One of those is phytanic acid, which acts like a hormone and helps the liver burn more fat, raising our energy expenditure. Another one is butyric acid, which has anti-inflammatory properties and may stimulate energy expenditure as well.

The researchers also looked at the associations between dairy intake and the risks of cardiovascular disease and type 2 diabetes. Again, they found no clear evidence that avoiding full-fat dairy offered health benefits. In fact, the stronger studies suggested there may be an inverse association between full-fat dairy consumption and type 2 diabetes. “We were intrigued by that because it’s a little counter intuitive,” Kratz said.

The Link Between Dairy Fat and Diabetes

Those unanswered questions led Kratz and his colleagues to conduct a second observational study that evaluated the relationship between dairy fat intake and various metabolic characteristics, including liver fat content. An accumulation of fat in the liver is a major risk factor for metabolic diseases, such as type 2 diabetes.

Rather than relying on participants to remember what they ate, Kratz measured biomarkers of dairy consumption, such as fatty acids that are unique to dairy, in the participants’ blood. The researchers then measured glucose tolerance, liver fat content, both hepatic and systemic insulin sensitivity, and the amount of insulin produced by pancreatic beta-cells.

And again, the results were counter-intuitive. Participants who ate the most dairy fat had lower levels of fat in their livers, as well as better insulin sensitivity and improved glucose tolerance.

Several recent observational studies in large U.S. cohorts had similar findings. One of these studies, published in a recent issue of Circulation, analyzed the blood of 3,333 adults enrolled in the Nurses’ Health Study of Health Professionals Follow-up Study. Participants who had the highest dairy fat intake, again measured by biomarkers in plasma, had up to 46 percent lower risk of developing diabetes over the course of the 15-year study.

More Conclusive Evidence Still Needed

The results were encouraging, but Kratz was still hesitant to offer any recommendations because the findings were based on observational studies, which can be flawed. Associations can be mistaken for cause-and-effect relationships, he explained.

I like to think of the Clinical Research Center as a really friendly place. I, and all of my team, enjoy coming here, and so do research participants. The staff is willing to go above and beyond to help you do your study.

Determined to come up with a more conclusive answer, Kratz decided to conduct a randomized clinical trial. The trial, which began in January, aims to determine the impact different types and amounts of dairy products have on blood sugar regulation and cardiometabolic health.

For the study, Kratz is recruiting 72 men and women with the metabolic syndrome—a group of risk factors, including insulin resistance, excess abdominal fat, and high cholesterol, that raise the risk for heart disease, diabetes, and stroke.

After completing a four-week diet of limited dairy, participants are randomly assigned to one of three 12-week dietary regimens:

  • Limited dairy (No dairy foods other than three servings per week of nonfat milk)
  • Three daily servings of non-fat or low-fat dairy
  • Three daily servings of full-fat dairy

The dairy products are weighed, packaged, and distributed to study participants via Fred Hutch’s Human Nutrition Lab. Participants are asked not to consume any dairy products outside those provided by the study. Other than the changes in dairy consumption, participants are asked to follow their regular eating habits.

The study will examine a broad range of endpoints, including changes in glucose tolerance, insulin sensitivity, pancreatic beta-cell function, liver fat content, and chronic systemic inflammation between the pre- and post-12 week intervention period.

Kratz will also measure changes in participants’ weight and fat content.  “If the people that recommended low-fat dairy are right, then consuming full-fat dairy should overall lead to a greater calorie intake and a gain in weight and fat mass,” Kratz said. “That will be a very interesting endpoint. Although we are giving people more calories in this arm, will that actually lead to people eating more and gaining weight?”

The tests will be conducted at the Institute of Translational Health Science’s Clinical Research Center in the UW Medical Center. “I like to think of the Clinical Research Center as a really friendly place,” Kratz said. “I, and all of my team, enjoy coming here, and so do research participants. The staff is willing to go above and beyond to help you do your study.”

Kratz added that he appreciates the staff’s professionalism. For the study’s oral glucose tests, participants’ blood needs to be drawn exactly 10, 20, and 30 minutes etc. after consuming a drink containing glucose. “It takes quite a bit of experience and skill to do that,” Kratz explained. “Also, you have to deal with the participant. You can’t get panicky. The research nurses are nice, professional, and they consistently get everything drawn the way we need it.”

Does all of this mean we can start gorging on full-fat dairy in hopes of improving our health? Not at all, Kratz said.

“Based on the current data, I’d say my best guess is that normal quantities of full-fat milk, yogurt, and cheese are most likely fine, and possibly even offer some health benefit. And I’d argue that currently there is no real reason to consume the low-fat varieties of these products,” he explained “At the same time, we really don’t have high quality data on whether low-fat or full-fat dairy is better for our health, and we may very well be surprised by the results of our trial. Personally, that’s why I’m excited about this type of intervention study. It really addresses a question that, in my mind, no one has a real answer for.”