The comparative health benefits of grass-fed beef are well documented. Scores of studies indicate that it’s higher in omega 3s. But when it comes to E. coli O157:H7, the advantages of grass-fed beef are not so clear. In fact, exploring the connection between grass-fed beef and these dangerous bacteria offers a disturbing lesson in how culinary wisdom becomes foodie dogma and how foodie dogma can turn into a recipe for disaster.
in the fall of 2006, when food activist Nina Planck wrote about the bacteria strain on the op-ed page of theNew York Times. At that time, people were getting sick from bad organic spinach, but the contamination seemed to have originated with herds of conventionally raised cattle that lived upstream. Not every animal excretes this nasty type of E. coli, she argued. “It’s not found in the intestinal tracts of cattle raised on their natural diet of grass, hay, and other fibrous forage. No, O157 thrives in a new—that is, recent in the history of animal diets—biological niche: the unnaturally acidic stomachs of beef and dairy cattle fed on grain, the typical ration on most industrial farms.”
he Times speaks, the world listens. Planck’s appraisal of grain- vs. grass-fed beef was highlighted on the Web sites for the Organic Consumers Association, the Center for a Livable Future, Grist, and Culinate.com, among other enviro-foodie venues. A few months later, Hannah Wallace of Salon warned that “a cow’s corn diet can also make us sick” on account of the acidic environment it creates for bacteria. Even Michael Pollan, perhaps the most widely read food writer on the planet, explained in a New York Times Magazine piece, “The lethal strain of E. coli known as 0157:H7 … was unknown before 1982; it is believed to have evolved in the gut of feedlot cattle.” These animals, he added, “stand around in their manure all day long, eating a diet of grain that happens to turn a cow’s rumen into an ideal habitat for E. coli 0157:H7.”
For many consumers, the case was closed: To avoid E. coli O157:H7, just eat grass-fed beef.
Unfortunately, the scientific evidence tells a very different story. Planck’s assertion seems to be based on a 1998 report published in the journal Science. In this study, the authors fed three cows a variety of diets in order to ascertain how feed type influenced intestinal acidity in cows and, in turn, how intestinal acidity influenced the concentration of acid-resistant strains of E. coli. They hypothesized that these strains would be especially dangerous to humans, since they could survive the low-pH environment of the human stomach. It turned out that grain-fed cattle did indeed have a much more acidic stomach than those fed grass or hay. And sure enough, they had a million times more acid-resistant E. coli in their colons.
This was good news for grass-fed beef: Eliminate grain from a cow’s diet and you’ll keep its intestines from getting too acidic and spawning dangerous, acid-resistant bacteria. There was only one catch. The authors of the Science piece never specifically tested for E. coli O157:H7. Instead, they guessed that the pattern of O157:H7 growth and induction of acid-resistance would mirror that of E. coli strains that are always living in the colons of cattle. If this assertion were true, E. coli O157:H7 would reach dangerous levels only in gastrointestinal tracts of grain-fed cows.
But between 2000 and 2006, scientists began to take a closer look at the effect of diet on E. coli O157:H7 specifically. A different set of findings emerged to indicate that this particular strain did not, in fact, behave like other strains of E. coli found in cattle guts. Most importantly (in terms of consumer safety), scientists showed in a half-dozen studies that grass-fed cows do become colonized with E. coli O157:H7 at rates nearly the sameas grain-fed cattle. An Australian study actually found a higher prevalence of O157:H7 in the feces of grass-fed rather than grain-fed cows. The effect postulated (and widely publicized) in the 1998 Science report—that grain-fed, acidic intestines induced the colonization of acid-resistant E. coli—did not apply to the very strain of bacteria that was triggering all the recalls.
What might explain this discrepancy? Scientists wondered whether there could be two subtypes of E. coli O157:H7 with varying degrees of acid-resistance. By that logic, the microbes from the grass-fed guts would be less resilient—and therefore less dangerous—than the ones that were growing up in the cows reared on grain. So they started running tests to find out.
Read more at: Beware the Myth of Grass-Fed Beef (Slate.com)
Thanks Autonomy Acres, for the story.
