A Low-Cost, High-Fat Diet Effectively Induces Obesity and Metabolic Alterations and Diet Normalization Modulates Microbiota in C57BL/6 Mice

Background/Objectives: High-fat diets (HFDs) are widely used to induce obesity, but cost-effective and reproducible formulations remain challenging. Moreover, the reversibility of metabolic and gut microbiota alterations following HFD withdrawal is not fully understood. This study evaluated a low-cost HFD model in mice and investigated metabolic, oxidative, and gut microbiota changes during a subsequent 12-week dietary normalization phase. Methods: Male C57BL/6 mice were fed a standard diet (CTN) or a lard-supplemented HFD for 12 weeks (Phase 1), followed by 12 weeks dietary normalization to a standard diet (Phase 2). Body weight, adiposity, blood glucose, biochemical parameters, and oxidative markers were assessed. Fecal samples were analyzed for short-chain fatty acids (SCFAs), microbiota composition (16S rRNA sequencing), and predicted functions using FAPROTAX and PICRUSt2. Results: The HFD significantly increased body weight, abdominal circumference, the Lee index, and adipose tissue mass compared to CTN. Following diet normalization, both groups exhibited weight loss, but the previously obese mice maintained a higher Lee index and distinct lipid and uric acid profiles. No hepatic oxidative stress was detected after normalization. SCFA profiles underwent a temporal shift: CTN showed higher fecal acetate, while HFD mice exhibited elevated butyrate. Functional prediction revealed one pathway associated with an unclassified Rickettsiales bacterium that was exclusively found in HFD mice. The CTN group exhibited a higher abundance of the thiamine diphosphate formation pathway (PWY-7357), suggesting enhanced oxidative metabolism. Conclusions: This low-cost HFD successfully induced obesity and dysbiosis. Dietary normalization resulted in a partial modulation of metabolic and microbial balance, thereby highlighting host–microbe metabolic plasticity.