Salt-mediated Reduction of Weight Gain in Sprague-Dawley Rats

High dietary salt levels have long been correlated with weight gain and obesity. Recent studies in the Skinner lab, however, have shown a reduction in weight gain in Sprague-Dawley rats fed a high salt, high fat (HS/HF) diet compared to those fed a high fat (HF) diet alone. This effect was not caused by increased activity levels of HS/HF animals, suggesting an alternative metabolic mechanism. To first determine if excess fat was being excreted through feces, we performed a fecal acid steatocrit analysis. Freeze dried fecal pellets collected from rats fed either a control, high salt, HS/HF or a HF diet were dissolved in perchloric acid and combined with .5% Oil-Red-O and then spun down in micro-hematocrit tubes. No significant difference in the proportion of excreted fat to overall feces was seen between groups. To then examine digestive efficiency, we performed bomb calorimetry. Pellets were made out of the collected freeze dried fecal matter and analyzed with a Parr 6200 bomb calorimeter. No significant differences in digestive efficiency were seen between groups. These results suggest that the mechanism of reduced weight gain is not due to the HS/HF group excreting more fat through their feces or because of a reduced digestive efficiency. They also reveal a more complex role of dietary salt in obesity, and further testing is required to fully elucidate the mechanism behind this salt-mediated reduction of weight gain.