Tuesday, October 13, 2009

Big Milk PhD bares her bias

Meet Dr. Susan Barr.

Dr. Barr is a professor of nutrition at the University of British Columbia and she has had a truly illustrious career, having published dozens of peer reviewed articles. She's also been a workhorse for the milk industry serving as a member of the Medical Advisory Board of the Milk Processors' Education Program, the Medical Advisory Board for the International Dairy Foods Association and speaking and writing regularly for the Dairy Farmers of Canada.

So what's got my knickers in a knot about Dr. Barr? It's her quotes from the recent "article" published in CanWest papers across the country last week where she tries to make the case that increased dietary dairy consumption reduces blood pressure. I put the word article in quotations because CanWest reports that the articles are "a joint venture with Dairy Farmers of Canada"and refer to them as a "special advertising feature".

Dr. Barr's case for dairy's role in reduction of blood pressure rests on a famous study from 1997, the Dietary Approaches to Stop Hypertension Study which resulted in what's now known as the DASH diet. Dr. Barr reports,

"The findings showed that those on the fruit and vegetable rich diet experienced a significant reduction in blood pressure. Those on the diet with milk products as well showed an even more significant reduction."
A true statement, except of course it omits the fact that the study was not designed to examine the specific effects of dairy on blood pressure and more importantly omits the fact that the diet with dairy had other differences from the fruit and vegetable rich diet including lower overall saturated fat, lower total fat and lower cholesterol.

Looking at the last 15 years of clinical trials research I was able to find only a handful of studies that were specifically designed to investigate the effects of dairy on blood pressure, and of those none were large or robust enough to draw firm conclusions.

Thankfully I was able to find a recent review article published in the Journal of the American College of Clinical Nutrition which summarized the most pertinent studies detailing dairy's effects on blood pressure. The review reported that a few studies indeed showed decreases in blood pressure with increased dairy, another showed increases in blood pressure with yogurt but not cheese, and many showed no dairy/blood pressure relationship at all. Regarding the DASH study the review specifically concluded,
"The greater reductions in BP seen with the DASH diet compared to the high fruits and vegetable diet cannot be ascribed to dairy products per se"
and the review goes on to conclude that there are certainly some plausible mechanisms by which dairy might improve blood pressure and that further research is warranted.

Fair enough, and really that's it? That's what's got me hot and bothered? The fact that Dr. Barr perhaps misconstrued the DASH study and overblew the preliminary suggestion that maybe blood pressure and dairy have a connection?


It was this. The review article summarized the only studies that have ever been published that were designed specifically to address whether or not an intervention involving increasing dairy would have a positive impact on blood pressure, all 5 of them. According to the review none of those studies showed significant improvements to diastolic blood pressure while 3 showed minor improvements to systolic pressure, the greatest of which was 5mm Hg.

Again, so? So why are you so pissy you're actually devoting an entire post to Dr. Barr and suggesting she's "bared her bias", yeah it doesn't look like there's much data to conclusively recommend increasing dairy for blood pressure benefit, but so what, at least there's some?

It was this. Included in those 5 studies was this one,
"Effects of increased consumption of fluid milk on energy and nutrient intake, body weight, and cardiovascular risk factors in healthy older adults"
This study, conducted in the year 2000, followed 204 healthy, middle aged men and women and tracked what happened to their blood pressure and their weight following randomization to either stick with their current diets (low in dairy) or to add 3 glasses per day of milk to their diets for 12 weeks. At the end of 12 weeks researchers found that the increased dairy group did not see any statistically significant reduction in their blood pressures (nor did the subgroup of pre-existing hypertensives in the sample), but they did see statistically significant increases in weight, triglycerides and blood sugar - not exactly healthful results.

Want to know who the lead author of this study, one of only 5 studies ever published which was actually designed to determine the effect of increasing dietary dairy consumption on blood pressure, the results of which showed increasing milk not only failed to have a positive effect on blood pressure but rather, significantly worsened weight, triglycerides and blood sugar? You guessed it, Dr. Susan Barr.

Ain't it funny (and by funny I mean awful) that she didn't mention the paucity of conclusive research linking increased dairy with decreased blood pressure along with her own study's negative and potentially harmful results while misrepresenting the findings of the DASH study in the "article", I mean "joint venture", I mean "special advertising feature" meant to sell more milk?

Kris-Etherton PM, Grieger JA, Hilpert KF, & West SG (2009). Milk products, dietary patterns and blood pressure management. Journal of the American College of Nutrition, 28 Suppl 1 PMID: 19571168

BARR, S. (2000). Effects of Increased Consumption of Fluid Milk on Energy and Nutrient Intake, Body Weight, and Cardiovascular Risk Factors in Healthy Older Adults Journal of the American Dietetic Association, 100 (7), 810-817 DOI: 10.1016/S0002-8223(00)00236-4

Appel, L. (1997). A Clinical Trial of the Effects of Dietary Patterns on Blood Pressure New England Journal of Medicine, 336 (16), 1117-1124 DOI: 10.1056/NEJM199704173361601