Does Diet Affect Outcome of Animal Studies?

Following many decades of studies employing laboratory mice and rats, new findings suggest that perhaps the results of these studies were influenced by the diet of the animals used in the studies.

The most common rodent chows used in labs today contain soy, which in turn contains phytoestrogens. These may enter the natural estrogen system of lab mice or rats and alter their physiology, whether male or female. An informal study of scientific journals recently conducted by the Dallas Morning News (Texas, USA) has revealed little or no description of the type of food given to research mice and rats. Of 50 articles involving these animals, only one mentioned that the protein source was soy. Phytoestrogens were never mentioned.

"You can design a wonderful study that will provide good information, but if you use the wrong diet, you may not even find anything,” said Julius Thigpen, a microbiologist at the U.S. National Institute of Environmental Health Sciences (Research Triangle Park, NC, USA). He noted that he became aware of this problem when other scientists approached him, puzzled that their experiments were suddenly producing different results. He suspected this was due to something in the feed. Later on, he discovered it was phytoestrogens. However, his research paper on the topic was rejected as not being important enough.

Another researcher, Leslie Leinwand, a molecular biologist at the University of Colorado in Boulder (USA), noticed a big difference when a particular breed of mice was switched from a soy-based diet to a milk-protein based diet to prepare for an experiment. The male mice in the study became much healthier on the milk-protein diet. Further studies showed the soy hormones to be part of the reason.

Another complicating factor is that chow formulas vary a lot, just as weather and geography affect the level of phytoestrogens in soy plants. Now, some researchers are asking for phytoestrogen-free chow. Still, it would be very difficult and costly to re-evaluate all of the animal research conducted to date or to repeat many of those experiments.

"The issue is going to be if you take 10 of those models that were tested on soy and put them on another diet, are you going to get different results?” asked Ms. Leinwand. "And not enough is known yet to say that.”

The U.S. government has scheduled a meeting between scientists and the manufacturers of rodent feed to look into this issue. The resulting recommendations will be submitted to a peer-reviewed journal.



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