Heat-processed rodent chow alters nutritive content and improves metabolic outcomes in insulin-resistant female mice

Animal research diets are often autoclaved for sterilization. Autoclaved chow can also serve as a model for investigating the health effects of heat-processed foods. Emerging evidence finds that heat-processed foods adversely affect human health. We hypothesized that autoclaved chow would further impair metabolism in a mouse model of androgen-induced insulin resistance.

C57BL/6J mouse breeding pairs were exposed to an autoclaved chow diet or a non-autoclaved, nutrient-matched control chow starting 2 weeks before mating and continuing through mating, pregnancy, and lactation. Diets were characterized by macronutrient and B vitamin analysis (B1, B5, B6), methylglyoxal and advanced glycation end products (ELISA), and reducing sugar content. Female 21-day-old weanlings received a 90-day continuous-release subcutaneous dihydrotestosterone implant to induce a polycystic ovary syndrome (PCOS)-like phenotype characterized by diet-independent, non-obese insulin resistance. Mice were kept on the assigned diet until experimentation 90 days post-androgenization. Metabolism was evaluated by measuring adiposity, fasting blood glucose and insulin, and glucose and insulin tolerance. Tissue markers of insulin signaling, methylglyoxal detoxification (GLO1), and inflammation (IL-6) were assayed via Western blot or quantitative PCR.

Consistent with previous literature, PCOS mice on the non-autoclaved diet developed excess adiposity, glucose intolerance, and insulin resistance. Unexpectedly, the autoclaved chow improved adiposity, glucose tolerance, and fasting insulin in PCOS mice. Diet characterization revealed no differences in macronutrients and no B vitamin deficiency in either diet, but a significant decrease in sugar content and a corresponding increase in methylglyoxal due to autoclaving. The autoclaved diet differentially modulated insulin signaling markers in skeletal muscle and adipose and GLO1 expression in liver. IL-6 expression was unaffected by diet in liver and adipose.

Autoclaved rodent chow improved the metabolic outcomes of a mouse model of PCOS. Despite nutrient-matching of the autoclaved diet by the manufacturer, we identified autoclave-induced discrepancies in sugar content and methylglyoxal. The autoclaved diet had tissue-specific effects on molecular markers of insulin signaling and methylglyoxal detoxification in PCOS mice, suggesting that diet preparation may be confounding animal studies. Our findings suggest that researchers should thoroughly validate and report dietary parameters in animal studies and consider them when interpreting and replicating findings.