State of Science :: Nutritional Quality
Study Compares Conventional, rbST/rbGH Free, and Organic Milk
A team of scientists recently tested conventional, rbST/rbGH-free, and organic milk samples bought at retail outlets (Vicini et al., 2008).
They measured "quality" characteristics (antibiotics and bacterial counts), "nutritional values" (fat, protein, and solids non-fat), and "hormonal composition." The team reports only minor differences across the three types of milk in most of these variables.
While the differences between these types of milk are slight, the study does find some significant results. The authors found that bacterial counts were lowest in conventional milk, but the differences were not "biologically meaningful." No antibiotics were detected in the samples. However, these samples were tested with relatively insensitive quick test-strip kits.
There were no major differences in the nutritional quality of the milk samples studied. Organic milk was higher in protein (3.22%) then the conventional (3.14%) and rbST-free (3.15%) samples. The authors counter that this represents less than 0.5% of the recommended daily protein intake for humans and is thus an insignificant difference. Also, this group of Monsanto scientists excludes form the study two nutritional quality parameters known to favor organic milk Conjugated linoleic acid (CLA) and omega-three acids.
The "Hormonal composition" of milk included testing for somatotropin (bST), insulin-like growth factor-1 (IGF-1), estradiaol, and progesterone. The concentrations of bST were very low across the board and did not vary significantly between samples.
The most interesting finding, not dwelled on by the authors, was that organic milk had by far the lowest level of IGF-1 level 2.73 ng/ml compared to 3.12 ng/ml in conventional milk (a reduction of 12.5%).
The authors report that because ultrapastuerization can degrade IGF-1, they did not include any organic milk that was, according to the label, ultrapasteurized. They note that some organic milk may still have been ultrapasteurized (although not labeled as such), thereby reducing the average IGF-1 level in organic milk.
The study also found that concentrations of the steroid hormones estradiaol and progesterone were highest in organic milk (6.4 pg/mL and 13.9 ng/mL respectively) and lowest in conventional milk (4.97 pg/mL and 12.0 ng/mL respectively). They point to differences in management practices at organic farms that could account for this, including feed intake and stages of lactation and pregnancy that the cows are milked at.
The authors conclude that
"It is important for food and nutrition professionals to know that conventional, rbST/rbGH-free, and organic milk are compositionally similar so they can serve as a key resource to consumers who are making milk purchase (and consumption) decisions in a marketplace where there are misleading milk label claims."
Source: "Survey of Retail Milk Composition and Affected by Label Claims Regarding Farm-Management Practices"
Authors: John Vicini, Terry Etherton, Penny Kris-Etherton, Joan Ballam, Steven Denham, Robin Staub, Daniel Goldstein, Roger Cady, Michael McGrath, and Matthew Lucy
Journal of American Dietetic Association, Vol. 108, No. 7, July 2008.