Failure to Ferment Dietary Resistant Starch in Specific Mouse Models of Obesity Results in No Body Fat Loss

Abstract

Resistant starch (RS) is a fermentable fiber that decreases dietary energy density and results in fermentation in the lower gut. The current studies examined the effect of RS on body fat loss in mice. In a 12 week study (study 1), the effect of two different types of RS on body fat was compared with two control diets (0% RS) in C57Bl/6J mice: regular control diet or the control diet that had equal energy density as the RS diet (EC). All testing diets had 7% (wt/wt) dietary fat. In a 16 week study (study 2), the effect of RS on body fat was compared with EC in C57BL/6J mice and two obese mouse models (NONcNZO10/LtJ or Non/ShiLtJ). All mice were fed control (0% RS) or 30% RS diet for 6 weeks with 7% dietary fat. On the 7 th week, the dietary fat was increased to 11% for half of the mice, and remained the same for the rest. Body weight, body fat, energy intake, energy expenditure, and oral glucose tolerance were measured during the study. At the end of the studies, the pH of cecal contents was measured as an indicator of RS fermentation. Results: Compared with EC, dietary RS decreased body fat and improved glucose tolerance in C57BL/6J mice, but not in obese mice. For other metabolic characteristics measured, the alterations by RS diet were similar for all three types of mice. The difference in dietary fat did not interfere with these results. The pH of cecal contents in RS fed mice was decreased for C57BL/6J mice but not for obese mice, implying the impaired RS fermentation in obese mice. Conclusion: 1) decreased body fat by RS is not simply due to dietary energy dilution in C57Bl/6J mice, and 2) along with their inability to ferment RS; RS fed obese mice did not lose body fat. Thus, colonic fermentation of RS might play an important role in the effect of RS on fat loss.

High-Amylose Resistant Starch Increases Hormones and Improves Structure and Function of the Gastrointestinal Tract: A Microarray Study

“…This is in contrast to our previous observations where rats fed HAMS-RS2 for 12 weeks had a significantly lower abdominal fat than the rats fed the EC diet [5, 9, 13]. Thus, HAM-RS2 needs to be consumed for more than four weeks to elicit effects on adiposity when rodents are consuming an equal energy density diet and the difference between diets is the presence of higher levels of fermentable carbohydrate .…”

“…Although the mechanism remains unclear, dietary resistant starches have been shown to decrease plasma cholesterol and triglycerides, increase insulin sensitivity, decrease fat storage, and produce anticancer effects in humans [1-13]. The current research is to gather gene expression data that will help identify mechanisms by which resistant starch improves health.…”

Resistant starch from high amylose maize (HAM‐RS2) reduces body fat and increases gut bacteria in ovariectomized (OVX) rats

“…OVX rats demonstrated increased bacterial levels with dietary HAM-RS2; however, their response was reduced compared to sham rats fed HAM-RS2 for all but Lactobacillus species. In a previous study, an obese mouse model failed to ferment HAM-RS2 (15). In the current study, OVX rats fermented HAM-RS2.…”

Dietary-resistant starch and glucose metabolism

“…Perhaps because of dosage issues, lifespan, anatomy or just species differences, current evidence suggests that animal models are failing to mimic humans in terms of the metabolic effects of resistant starch. Ad libitum resistant starch feeding in rodent models consistently leads to weight and fat loss [17,18,29,31,32]; however, in humans there is no evidence for this [15,16 & ]. With this caveat for the extrapolation of animal data to humans, the need for high-quality human clinical trials cannot be substituted by animal models.…”