October 2016 Issue
The Truth About Dairy Fats
By Carrie Dennett, MPH, RDN, CD
Vol. 18, No. 10, P. 26
In the debate about saturated fats, where does full-fat dairy fit?
People have been making cheese for about 8,000 years, but whether cheese—along with butter, cream, and other full-fat dairy products—can be part of a health-promoting diet remains controversial.1 The connection between saturated fats and cardiovascular disease (CVD) has been called into question in recent years,2-7 and so has the assumption that all saturated fat-rich foods are nutritionally equal. Nutrition science is gradually shifting from focusing on isolated nutrients to considering how all the nutrients and other elements of a food work together to promote or prevent disease.5 Will this open the dietary door to higher-fat dairy foods?
Saturated Fats to CVD: Missing Links
The recommendation to reduce dietary saturated fats has its origins in epidemiological associations first drawn 70 years ago between saturated fats, blood cholesterol, and CVD.8 Despite clinical evidence that high intake of saturated fats raises cholesterol in humans and pharmacological evidence showing that lowering LDL cholesterol reduces risk of heart attack and stroke, the idea of a causal relationship between saturated fats and CVD remains controversial, mostly because a physiological mechanism hasn't been identified.9,10
The Dietary Guidelines for Americans,11 American Diabetes Association,12 World Health Organization,13 and Academy of Nutrition and Dietetics14 all recommend keeping saturated fat intake below 10% of calories. The American Heart Association recommends less than 5% to 6% of total calories from saturated fats.15,16 To help achieve this goal, all groups recommend nonfat or low-fat dairy, including milk, yogurt, and reduced-fat cheese.
Are All Saturated Fats Created Equal?
Even though saturated fat remains a "nutrient to limit," the Dietary Guidelines Advisory Committee (DGAC) said in its 2015 report that more research examining the effects of saturated fat from different sources is needed, because different sources of saturated fat contain different fatty acid profiles, which may result in different lipid and metabolic effects.17
"Every food has a combination of fatty acids," says Marian Neuhouser, PhD, RD, a member of the 2015 DGAC, president of the American Society for Nutrition, and a nutritional epidemiologist with the public health sciences division of Fred Hutchinson Cancer Research Center in Seattle. "We tend to say that animal foods are highest in saturated fat, and they are, compared to plant sources, but they also have polys and monos."
Mario Kratz, PhD, MS, a faculty member at Fred Hutchinson Cancer Research Center and the University of Washington in Seattle who conducts nutrition research, says that because saturated fats raise the ratio of LDL to HDL cholesterol "relatively modestly, researchers assumed cutting back on all sources of saturated fat must be a good thing. "They put all sources of saturated fat in the same basket. That's my major gripe with the discussion on saturated fats," Kratz says.
About 70% of the fatty acids in milk are saturated; 25% are monounsaturated (MUFAs); and 2.3% are polyunsaturated (PUFAs). However, there are more than 400 types of fatty acids in milk, including many that we don't get in significant amounts from other foods.18,19 Kratz says that even though some of these fats are present only in small amounts, they may be biologically relevant and beneficial, either alone or in synergy with each other. That includes some of the saturated fats.
In the Multi-Ethnic Study of Atherosclerosis, different saturated fat-rich foods had different effects on CVD risk. Saturated fatty acids from meat were associated with higher risk of CVD, while dairy fat was associated with a lower risk. The authors concluded that something about dairy foods may minimize the association between saturated fats and CVD.20 That something could be the milk fat globule membrane (MFGM). Milk fat occurs as globules emulsified in the liquid component of milk, and the membrane has unique structural properties.18,21,22
"I think this is one of the more exciting aspects of the research on dairy fat in that it could go a long way to determining the 'why' part of the dairy fat research puzzle," says Mickey Rubin, PhD, vice president of nutrition research for the National Dairy Council. "Clearly, dairy fat is unique from other dietary fats given the structure of the milk fat globule membrane, and some research has indicated that this is one of the drivers, if not the driver that differentiates dairy fat's health effects," he says, adding that cheese23 and cream24 don't raise LDL cholesterol as might be expected based on their saturated fatty acid content. Butter, which has little MFGM, does.
Dairy Research: Epidemiologic vs Intervention
Research supports the benefits of dairy for health and reducing disease risk. But dairy fat still draws a question mark, largely because there's some discordance between evidence from long-term prospective cohort studies, which shows neutral or beneficial associations between dairy fat and CVD risk, and short-term clinical trial data, which consistently show that butter and whole milk increase cholesterol and other blood markers linked to CVD risk.9
"Moving forward, I think we need more research on whole foods rather than nutrients," Rubin says. "In the end, it is the whole package of a food that contributes to a health effect, and people eat foods, not nutrients."
The primary rationale for limiting dairy fat has been to reduce intake of LDL-raising saturated fats and decrease the risk of obesity by lowering calorie density in the diet.19 "Americans were advised to consume dairy fats in the low-fat or nonfat categories, even though it had never been conclusively shown by research, interventional or observational, that there was a good reason for that," Kratz says.
Neuhouser says that the additional research needed to reach stronger conclusions about the role of saturated fats in health may be a long-term proposition, so questions posed at the time of the 2015 DGAC report may not be answerable when the 2020 DGAC convenes. "A lot of the studies that are needed to answer these questions require funding and large sample sizes," she says, noting that research on dairy tends to be better funded.
Dairy and Disease Outcomes
Kratz sees a flaw in basing the longstanding advice to reduce saturated fats on epidemiological associations between dietary fat and health outcomes. "If you think about the last 30 to 40 years, the people who eat the most saturated fatty acids, they have other dietary and lifestyle characteristics that we would call less healthful." For example, dietary saturated fat intake in the United States is strongly associated with smoking, intake of trans fats, low fiber intake, and lack of physical activity.22,25 "When researchers adjust for those associated dietary lifestyle factors, those associations [between saturated fats and CVD] typically go away," he says. "In my mind, there may have been associations between saturated fatty acids and coronary heart disease, but there's never been a convincing [causal] link."
For the most part, prospective cohort evidence suggests that consumption of milk and other dairy products (other than butter) has a neutral or favorable effect on CVD risk.9,26-29 That includes higher-fat and lower-fat dairy.30 There's no consensus from clinical studies on whether lower-fat dairy foods are associated with a reduced risk of CVD, and there are few randomized controlled trials that directly compare full-fat with lower-fat alternatives.26
"To really have conclusive evidence on what the issue is, we need randomized controlled trials," Kratz says. He's currently conducting a controlled feeding trial to assess the impact on cardiometabolic health after 12 weeks of three daily servings of either full-fat dairy or low-fat and nonfat dairy, or very limited amounts of any dairy.31 "I really don't know what the result will be," he says, adding that even a null result would be interesting.
Prospective cohort studies, and the meta-analyses and systemic reviews based on them, suggest that overall dairy intake is associated with reduced risk of metabolic syndrome and type 2 diabetes,9,32-35 with some studies referring to low-fat dairy products specifically and others to dairy products in general.18 Evidence suggesting a protective effect is strongest for overall low-fat dairy and yogurt and weakest for milk and full-fat dairy, with some evidence specifically supporting cheese.18,32,35,36
Although some studies suggest that dairy fat has a negative impact on diabetes risk, perhaps due to specific saturated fatty acids,19 data from the 26,930 participants in a Swedish cohort revealed a decreased risk of type 2 diabetes with high intake of full-fat dairy but not with low-fat dairy. The strongest associations were for cream and full-fat fermented milk (including yogurt) and for cheese among female participants.37
Dariush Mozaffarian, MD, DrPH, dean of the Tufts Friedman School of Nutrition Science and Policy in Boston, says that many dietary recommendations in the 1970s and 1980s were made through the lens of preventing heart disease. "I think now the guidelines are seeing things through the lens of obesity," he says, adding that this is one reason for continued disagreement about high-fat dairy among scientists. "They start with the saturated fat argument, but they morph into the calorie argument." He points out that the quality of the food you eat affects health and metabolism and long-term weight control. "Counting calories is not the be all end all."
Researchers have hypothesized that dairy fat contributes to obesity, but Kratz says full-fat dairy, not low-fat dairy, is consistently associated with more beneficial weight outcomes,19 acknowledging that some of this association may be due to reporting bias or reverse causation. In other words, people struggling with their weight may underreport intake of full-fat dairy or tend to choose low-fat dairy products. "Yogurt and milk, even in full-fat versions, aren't especially calorically dense foods," Kratz says. Cheese is, but most people eat that in smaller amounts.
Quantity vs Quality: The Dairy Food Matrix
For all the talk about saturated fatty acids, dairy foods are more than just vehicles for fat. Dairy foods, like other foods, are a complex matrix of vitamins, minerals, proteins, and carbohydrates as well as saturated fats, MUFAs, and PUFAs. Could part of the controversy and inconclusiveness about the role of saturated fats in health and disease be because the type of saturated fats—and the other qualities of the food it's packaged in—matters, even when supplying the same amount of fat?38
"There's still a lot to learn, especially with dairy and dairy fat," Mozaffarian says. "I think for decades we've been giving recommendations based on nutrients in food, not on foods themselves. It's critical to have food-based research not just because of the difference in saturated fats but also because of all the other components in dairy"—for example, calcium and vitamin D. "All of our guidance on dairy is based on nutrient science. We don't want saturated fat, but we want these other components, so we recommend low-fat dairy. It's a very deconstructionist, reductionist approach."
Kratz says it's hard to isolate dairy fat intake from the food in which it's consumed, especially in observational studies, and that any disease association found for dairy fat intake could be explained by other food components, such as sugar in ice cream or refined carbohydrates in pizza and fast food. It also may be explained by overall dietary patterns and lifestyle. "People who eat a lot of dairy in the form of cheeseburgers or pizza are not likely to eat those foods with big piles of green leafy vegetables," he says. "They may also be less likely to do other healthful things in their lifestyle."
Evidence does suggest that not all milk fat-containing dairy products have the predicted effect on blood lipids and cholesterol.22,39,40 One of the few observational prospective studies looking at the association of individual dairy foods with CVD incidence found that while total dairy intake was significantly associated with a lower risk of myocardial infarction (MI), individual dairy products appeared to have different associations with MI risk. No difference between low-fat and full-fat versions of specific dairy food products and MI risk was observed.40
"I foresee that in the future our recommendations will be about different foods, instead of nutrients," Mozaffarian says. For example, "instead of recommending low-fat or high-fat dairy, recommending yogurt and cheese."
Benefits of Fermentation
So far, it appears that fermented, cultured dairy products like yogurt and cheese have an edge over butter and even whole fluid milk. Together, epidemiologic evidence looking at health outcomes,28,34,41,42 and interventional studies looking at blood lipids,9,23,43,44 glucose, and insulin suggest that yogurt and cheese aren't associated with CVD or diabetes.22,39,45 Yogurt intake also is associated with reduced risk of weight gain.35
This is likely due to both the probiotic bacteria in fermented foods as well as the bioactive fat-soluble compounds that are produced with long fermentation times, as seen in traditionally produced cheeses. Kratz says European countries have higher consumption of full-fat yogurt and traditional cheeses than the United States, yet the United States is one of the few countries to find associations between high-fat dairy intake and CVD.
How Should Dietitians Advise Patients?
As the research suggests, this is a nuanced issue that can't be answered with a sound bite. "I think the data do suggest that there are differences between full-fat and low-fat dairy, and that full-fat dairy may be more beneficial," Kratz says, adding that his own family consumes full-fat dairy. "We really never had really good evidence to recommend nonfat or low-fat dairy products."
"Ten years ago, I would have recommended swapping out full-fat dairy with skim options without blinking an eye. Now, the research is showing that it might not matter so much," says Alexandra Caspero, MA, RD, CLT, RYT, owner of DelishKnowledge.com and cocreator of the Joyful Eating, Nourished Life program. "I think as RDs, our job is to help consumers focus on what matters most. If someone's only eating yogurt a few times a week, I don't split hairs over full-fat vs low-fat, as it doesn't matter so much in the big picture."
Judy Simon, MS, RDN, CD, CHES, of Mind Body Nutrition in Bellevue, Washington, says that while she may advise against consuming large amounts of full-fat dairy for caloric reasons, she often recommends that her fertility patients include a serving of full-fat dairy with berries. "They find it to be delicious, flavorful, and satisfying. Knowing that it's nutrient dense and might help with their fertility,46 they like it."
It appears that yogurt, cheese, and other fermented dairy foods may offer the greatest benefits for health, but as for butter, it's not exactly "back." A June systematic review coauthored by Mozaffarian found that butter is, in fact, neutral.47 Better options would be fats and oils rich in MUFAs and PUFAs, which have demonstrated benefits for health.48
Kratz says that an isolated fat like butter may not be much different than isolated amounts of refined carbohydrates in terms of nutrition. "Even if now we're turning around the story a little bit ... I think we shouldn't go too far in the other direction," he says. "It's not OK to eat limitless amounts of isolated fats."
Mozaffarian adds that many people who choose low-fat dairy end up compensating for those calories in other ways that aren't healthful, so their diets are worse. "We're so far away from optimal diets. I think we should focus on the handful of things that are the absolute best and the handful of things that are the absolute worst, and let people know that the rest are in the middle and there are things we don't know yet."49
— Carrie Dennett, MPH, RDN, CD, is the nutrition columnist for The Seattle Times and speaks frequently on nutrition-related topics. She also provides nutrition counseling via the Menu for Change program in Seattle.
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