With commentary by researcher Frank Hu, MD, MPH, PhD, professor of nutrition and epidemiology, Harvard Medical School and T.H. Chan School of Public Health.
The debate about high-fat versus low-fat dairy foods is simmering again.
In the latest study, adults who consumed more full-fat dairy products (as reflected by higher levels of certain fatty acids in their blood samples) had a lower risk of getting type 2 diabetes over a long-term follow-up.
In some press reports, that finding was translated to mean it's time to switch to whole-fat dairy foods, despite current dietary guidelines that suggest choosing low-fat or non-fat dairy as part of a healthy diet.1
Not so fast, says Frank Hu, MD, PhD, MPH, professor of nutrition and epidemiology at Harvard Medical School and the Harvard T.H.Chan School of Public Health and a study coauthor. "I wouldn't use this research to give a green light for people to drink whole milk [or other high-fat products]," he says. "This is a very preliminary result."
Dr. Hu and his colleagues followed more than 3,300 adults, ages 30 to 75, enrolled in two different long-term studies. One, the Nurses' Health Study, began in 1989. The other, the Health Professionals Follow-Up Study, began in 1993. The researchers tracked the men and women through 2010. During that time, 277 new cases of diabetes were diagnosed.
The researchers then looked at blood samples taken at the start of the studies, measuring circulating levels of fatty acid biomarkers found in high-fat dairy foods. The higher these biomarkers, the lower the risk of getting diabetes, with the risk reduction ranging from 43 to 52%. The link held after adjusting for lifestyle, diet and other factors. The study was published online March 22 in Circulation.
In a previous study, Dr. Hu and his colleagues found that a serving a day of yogurt reduced the risk of type 2 diabetes, but that other dairy foods did not affect risk.2 Even so, he says, he still wouldn't advise people to switch to full-fat dairy. Rather, the study results should guide further research, Dr. Hu says.
The fatty acid biomarkers studied in his recent research, he says, ''make up a small percent of the total dairy fat. It doesn't necessarily represent the health effects of the entire product."
"To make a recommendation [about which fat content to eat], you have to look at the whole food, instead of just parts," Dr. Hu says.
Researchers aren’t sure. "The association could be due to metabolic effects of the fatty acids instead of a direct effect," Dr. Hu says. There is much to learn, he says.
Other experts say that eating low-fat dairy may keep people hungry, and then craving carbohydrates. Eating a carbohydrate-heavy diet tends to add weight, which can boost the risk of type 2 diabetes.3
"This is one study, and it is a report of an association [not cause and effect]," says DiabeticLifestyle Medical Advisory Board Member J. Michael Gonzalez-Campoy, MD, PhD, medical director and CEO of the Minnesota Center for Obesity, Metabolism and Endocrinology. He reviewed the findings.
"Therefore, there should not be any recommendations made based on this one study," he says. One explanation for why full-fat dairy reduces risk is the idea that the higher fat keeps people from eating too many carbohydrate-rich foods, as some experts propose, he says.
On the other hand, those with low levels of the biomarkers may be substituting high-calorie drinks such as sodas for milk and that can drive up weight and raise diabetes risk. "It may be the absence of the markers [not their presence] that confers the risk," he says.
"When all is said and done, milk and dairy products are highly recommended as a source of high-quality protein and calcium," Dr. Gonzalez-Campoy says. "Removal of fat simply helps decrease caloric load. Thus, the current recommendations to incorporate low-fat dairy products into meal planning still hold."
"In this study, it appears the consumption of dairy products as evidenced by these biomarkers being present in the blood contribute to a lower incidence of diabetes," says Scott Cunneen, MD, director of bariatric surgery at Cedars-Sinai Medical Center, Los Angeles, and a member of DiabeticLifestyle's Medical Advisory Board. However, he cautions: "It doesn’t indicate it’s the fat that is the causation of that. It's an interesting preliminary result, but it clearly isn’t a cause-and-effect relationship."
Dr. Hu agrees. "I think it's really premature to recommend full-fat dairy products for anybody," he says.
Researchers are still looking at the effects of high-fat dairy on obesity and heart disease risk, two other concerns of those who have diabetes. Some studies have found that high-fat dairy does not seem to contribute to obesity or to heart disease risk factors, and may actually be protective. But experts say the findings are not yet conclusive.