July 23, 2008
Study explores soy’s effects on diabetes and obesity
CARBONDALE, Ill. -- Maybe the “good” bacteria in yogurt and diet supplements have a dark side.
A small-scale rat study involving two bacterial species commonly used in these products led to increased body fat and the early onset of diabetes -- exactly the opposite of what the researchers from Southern Illinois University Carbondale expected to find.
“We’d already found that soy diets can influence weight gain and improve blood glucose,” said D. Allan Higginbotham, a nutritionist in SIUC’s College of Agricultural Sciences.
“As we know natural bacteria found in the colon can metabolize undigested parts of soy, the original contention was that if we could use dietary supplements to change the bacteria in the gut to favor those known to have health benefits, we might be able to boost soy’s effects.”
To test the idea, Michele M. Martin, a graduate student from Lima, Ill., who based her thesis on this research, mixed up three different soy-based diets -- one including carbohydrates that encourage bacterial growth, each of the other two containing a specific type of beneficial bacteria -- and fed them to rats bred to be fat. A control group ate standard chow.
“We were hoping that one or more of the diets would delay the onset of diabetes in this particular rat,” Higginbotham said.
“We’ve used them before, and we know that a diet formulated to induce diabetes will do so within the space of a few weeks.”
The special diets didn’t dampen the rats’ appetites -- one of Higginbotham’s concerns at the study’s start -- but they didn’t help the rats slim down any either.
“We were hoping that soy would have an anti-obesity effect, but there were no differences in body weight,” Higginbotham said.
The diets did, however, affect the percentage of fat each rat carried.
“One of the bacterial diets produced a higher rate of body fat than all the other groups,” Higginbotham noted.
While the blood glucose numbers were not statistically significant, the researchers noted a trend in those rats on both bacterial diets toward elevated levels. The levels were high enough that the study ended six weeks early to avoid having the rats die of diabetes.
Because this study turned their hypothesis upside down, the researchers want to have a second go. This time around, they propose giving the rats a round of antibiotics to kill off existing bacteria, then starting over with the same diet regimen.
“Just because we fed the rats these diets doesn’t mean we were affecting the population of microflora,” Higginbotham said.
“Something could have happened before the bacteria got to the colon (which is where all the action takes place). In this second study, we’re going to try to tie in what’s happening in the colon with the physiologic results of how the animals actually respond to the diets.”
If the second study produces the same results as the first, it could help explain the contradictory conclusions of many earlier rat and human studies regarding soy’s effects on diabetes and obesity.
“There’s been such a variable response; it’s possible that bacteria could account for that,” Higginbotham said.
“It may be that having the ‘wrong’ bacteria in your gut can decrease the effects.”
The results may also indicate the wisdom of taking a closer look at these particular bacteria, given their presence in products intended for human consumption.
“As far as I know, there have been no studies showing that they had side effects or negative consequences,” Higginbotham said.
“This would be the first.”