Dairy Data Deliver Mixed Messages

Advertisements touting the benefits of milk and other dairy products forpeople who want to slim down and boost their health are everywhere—andare causing a bit of a buzz.

Two lawsuits filed in June by the Physicians Committee for ResponsibleMedicine (PCRM) argue that several food manufacturers and the dairy industryhave fraudulently promoted dairy's weight-loss powers through a deceptiveadvertising campaign.

Indeed, some patients may be putting greater faith in the weight-lossconnection than is warranted at this point, say medical and nutritionalexperts familiar with the underlying research.

“There has definitely been some interesting data that suggest theseeffects from milk, but we need to replicate the findings with more and biggerclinical studies before we can actually say without a doubt that there's animpact,” says Marie-Pierre St-Onge, PhD, an assistant professor ofnutrition sciences at University of Alabama at Birmingham who has reviewed theresearch.¹ St-Ongewas a researcher and instructor of medicine at Columbia University's ObesityResearch Center in New York when she conducted her review.

THE EVIDENCE

To date, most of the data suggesting a role for dairy in weight loss havecome from several observational and cross-sectional studies or from reanalyzeddata culled from studies originally designed to look at different end points,such as bone loss. (A comprehensive list of observational and other studiessupporting a possible link between optimal dairy consumption and weight losscan be found on the National Dairy Council Web site atwww.nationaldairycouncil.org/nationaldairycouncil/healthyweight/science.asp.)

Two large observational studies also have identified a link between dairyconsumption and a reduced risk for developing insulinresistance² and type2 diabetes³ inoverweight adults. However, those with a family history of diabetes appearedto reap no risk-reductionbenefit.³

According to Joan Lappe, PhD, RN, professor of nursing and medicine atCreighton University in Omaha, Neb., who has studied the relationship betweendairy consumption and weight in younggirls,⁴ the bestevidence so far linking optimal dairy consumption (three daily servings) andweight loss comes from a handful of randomized clinicaltrials.^5–8The studies were small, each including 32–68 participants. But theresults indicated girls who consumed optimal amounts of dairy products lostalmost twice as much weight and midsection fat as their counterparts, who atethe same total calories but less dairy.

Supplemental calcium had a positive though weaker correlation with weightloss in some of thesestudies.^6,7“I think it's at least safe to say that people shouldn't be cutting milkout of their diets just because they're worried about fat content,”Lappe says.

“Low-fat milk is a wonderful low-calorie source of nutrients,”she says. As for helping to control weight and reduce body mass index (BMI),“more research would give us more confidence on that issue.”

It's also important to note that, according to researchers, the weight-lossbenefits of dairy have been found only in very specific circumstances.

Michael Zemel, PhD, professor of nutrition and medicine and director of theUniversity of Tennessee Nutrition Institute, is the lead investigator on allof the randomized research supporting the dairy–weight loss connectionto date. That research is supported in part by grants from the National DairyCouncil and various food manufacturers, which has raised some eyebrows. Zemelsays the food industry funding does not influence his data.

“Sure they have a self-interest, and that's why I approached them forfunding and knew they'd be interested in supporting this work,” Zemelsays. “Research is very transparent. You'd have to be an idiot to letyour funding source influence your results, because if someone else can'treplicate that data, there goes your reputation and your career.”

St-Onge agrees that companies fund research all the time and must be readyfor the possibility of negative results. “I am not concerned that Dr.Zemel's funding source is the National Dairy Council,” she says.“Needless to say, however, that data must always be replicated byindependent groups before firm conclusions can be made.”

MILK NOT A WEIGHT-LOSS PRESCRIPTION FOR EVERYONE

“The research has never shown that milk is a magic eraser,”Zemel says.

In his clinical trials, all participants were overweight or obese adults,and all were placed on reduced-calorie diets with controlled low or high diaryintake during the 12- to 24-week studyperiods.^5–8Whether his findings translate to other groups is unclear. But a recentyear-long randomized trial found no link between improved dairy consumptionand weight loss in 150 healthy, normal-weightwomen.⁹

Reducing calories also counts, says Elisa Zied, MS, RD, nationalspokesperson for the American Dietetic Association.

“The bottom line with weight management is always calories in,calories out,” Zied says. “If you're adding milk products to yourdiet to lose weight, you need to create a calorie deficit and reduce yourcalorie intake from other foods, especially those that are high in calories orfat and low in nutrients. If you simply add milk products to lose weight, youmay actually take in too many calories.”

That point was highlighted in a recent observational study of nearly 13,000adolescents that found those consuming more than three daily servings of milkin a given year increased theirBMI.¹⁰ “Theadded calories appeared responsible” for the increased weight, theauthors conclude.

Likewise, Zemel says his data also do not support consuming more than theDepartment of Agriculture (USDA)-recommended three daily servings ofdairy.

“We're not talking about milk having a pharmacological effect. We'retalking about the fact that most Americans don't get the optimal amount ofcalcium or dairy,” Zemel says. “Our data don't show any benefitfrom simply drinking more milk if you're already consuming enough.”

In another recent randomized study, Australian researchers found nodifference in weight and BMI reduction between two groups of 25 overweightadults fed different reduced-calorie, high-protein diets for 12 weeks. Thosewho had the high-dairy variation lost about the same amount as those on ahigh–mixed-proteindiet.¹¹

“It's hard to compare,” St-Onge says. The high-dairy diet hadmore than twice the recommendation of the Food and Nutrition Board of theInstitute of Medicine for calcium at 2,400 mg, whereas the low-dairy dietstill included near-optimal calcium intake of 800–900 mg.“Australian milk is also not vitamin-D fortified, so that may have beena factor,” she says.

In the meantime, the dairy debate likely will rage on, at least in thecourts. Whether the arguments are medical or political or both depends onwhere one stands. The International Dairy Foods Association (IDFA), one of theparties accused of fraudulent advertising by PCRM, contends in a writtenstatement that “a growing body of research continues to strengthen theconnection between dairy consumption and weight management.” Theassociation says the views of PCRM are closely aligned with those of animalrights groups, and physicians represent only 5% of its membership.

PCRM maintains that “scientific evidence contradicts the dairyindustry's weight-loss claims.” Kraft Foods, Inc., another target in thesuit, has pulled advertisements—such as a cheese package in the shape ofan hourglass—that suggest dairy products encourage weight loss.Subsequently, Kraft has been dropped from the lawsuit. ▪

More Research to Come on Dairy–Weight Loss Links

Additional research is under way to clarify the possible link between dairyand weight loss, as well as reduced risk for type 2 diabetes. Some studies arefocusing on possible mechanisms.

One theory involves the increase in the calcium-preserving hormonecalcitriol that occurs when the body is deprived of sufficient calcium. Thatprocess also may trigger lipogenesis and inhibit lipolysis, fat oxidation, andadopocyte apoptosis—in essence, increasing body fat. Another theory isthat dairy-derived angiotensin-converting enzyme (ACE) inhibitors may suppressangiotensin 2, which promotes fatsynthesis.

In terms of diabetes, one hypothesis involves the insulinotropic propertiesof whey proteins in milk. Another involves milk's high magnesium content.Prospective studies have shown an inverse relationship between magnesium-richfoods and diabetes.

“I think we have a lot of interesting research to look forwardto,” says Om Gonda, MD, of the Joslin Diabetes Center at Harvard MedicalSchool in Boston. “Still, there is a lot of evidence that people shouldkeep up with optimal amounts of calcium in their diets, and a good way to addthat without adding lots of extra calories is to stick to low-fat dairysources.”

Pass It on to Your Patients

Weight management is always about balancing calories in and caloriesout. The bottom line about dairy and weight loss: Eat three dailyservings of low-fat dairy to meet the adequate intake for calcium.

One of the recommendations of the 2005 USDA Dietary Guidelines forAmericans is to “consume 3 cups per day of fat-free or low-fat orequivalent milk products.” (USDA made the recommendation to helpreduce the risk of bone mass loss and contribute to important amounts ofmany nutrients.¹ Itwas not made with weight loss in mind.)

One cup is equivalent to:

1. 1 cup low-fat or fat-free milk,

2. 1 cup low-fat or fat-free yogurt,

3. ⅓ oz low-fat or fat-free natural cheese (cheddar, mozzarella, Colby,etc.), or

4. 2 oz low-fat or fat-free processed cheese (e.g., American processedcheese).

Note that each equivalent contains, on average, between 300 and 350 mgcalcium. The adequate intake for calcium is 1,000 mg/day for adults19–50 years of age and 1,200 mg/day for adults >50 years. So 3 cupsof low-fat dairy a day should be a good start in reaching the calcium intakegoal.

In amounts commonly eaten, milk products such as fat-free cottage cheese,fat-free sour cream, and fat-free cream cheese do not provide as much calciumas these examples, and so were not included in the equivalencedefinition.

Replace calorie-dense, low-nutrient foods in your daily meal plan withfat-free or reduced-fat milk equivalents. Don't add more servings.Whether or not you lose weight, you should not gain weight, and you willimprove your bone health if you incorporate three milk equivalents a day intoyour meal plan.