Best Practices for Diet-Induced MASH B6 Mice: Mouse Models for Metabolic Disease Research

Introduction: Advancing Preclinical Obesity and MASH Research

Metabolic dysfunction-associated steatohepatitis (MASH) and obesity remain critical areas of focus for preclinical research, offering translatable insights into human metabolic disease. However, designing studies that deliver reproducible, meaningful results can be challenging. 

In this webinar, Best Practices for Diet-Induced MASH and Obesity Studies, Dr. Laura Griffin outlined practical strategies for optimizing study design, highlighting how diet formulation, rodent strain, housing, and preconditioned models can dramatically influence outcomes. 

Optimizing Diet Formulation for Diet-Induced MASH Mice

Not all “high-fat” diets are created equal. Early approaches often involved adding lard to standard chow, but this method inadvertently diluted other nutrients, such as vitamins and minerals, leading to confounding results.

Purified ingredient diets now provide a more precise and reliable solution, allowing researchers to adjust fat, carbohydrate, or nutrient levels while maintaining consistency in caloric content and micronutrient composition. This precision makes it possible to model both obesity and MASH more consistently.

Even the type of fat matters: saturated fats such as lard or tallow induce obesity more effectively than unsaturated fats like olive oil. For MASH, obesogenic diets that combine fat, fructose, and cholesterol more closely mimic the human condition compared to nutrient-deficient diets, which may act quickly but lack translational relevance.   

Rodent Strain Selection for Obesity and MASH Studies

Selecting an appropriate rodent strain is just as important as diet design. C57BL/6 mice are widely used in metabolic research due to their susceptibility to weight gain and liver disease, but not all substrains are identical.

For example, “J” and “N” substrains differ in their mitochondrial metabolism due to a loss-of-function mutation in the Nnt gene in "J" substrains. This subtle difference can affect weight gain and disease severity, making it crucial to know which substrain you’re working with when comparing results across studies or publications.

Other species, such as rats, hamsters, and even guinea pigs, have unique advantages depending on the phenotype under investigation. Understanding these nuances helps ensure that the chosen model aligns with study goals.

Housing and Environmental Conditions in MASH Mice

Environmental conditions play a surprisingly large role in study outcomes. Housing temperature is one example: while standard vivarium temperatures are below the rodent thermoneutral zone, raising housing temperatures can accelerate MASH progression and even make female mice susceptible to disease phenotypes typically limited to males.

Cage density also influences both weight gain and aggression. Housing mice in groups of three to four strikes the right balance between minimizing thermal stress and reducing social conflict. Other factors, such as bedding, enrichment, and microbiome consistency, further contribute to reproducibility.

Ignoring these details may result in phenotype variability that can complicate data interpretation.

Benefits of Off-the-Shelf Preconditioned Mouse Models

One of the most exciting developments highlighted in the webinar is the availability of preconditioned, off-the-shelf models, such as DIO B6 and MASH B6 mice. Researchers can purchase animals maintained on specialized diets instead of waiting 12–30 weeks for in-house conditioning.

This approach offers several advantages:

Practical Considerations for Designing Diet-Induced Studies

Dr. Griffin also addressed several practical aspects often overlooked in early planning stages. These include ensuring sufficient freezer space for high-fat diet storage, accounting for weight loss due to shipping stress, and carefully defining acclimation periods.

Even small details, such as the frequency of diet changes or the choice of water treatment, can impact outcomes. By planning ahead and maintaining consistency across cohorts, researchers can reduce variability and improve confidence in their findings.

Conclusion: Building Reliable MASH and Obesity Models

The design of diet-induced obesity and MASH studies is far more complex than simply feeding rodents a high-fat diet. Success depends on integrating careful dietary formulation, appropriate strain selection, environmental control, and practical husbandry.

Watch the Full Webinar On-Demand

To gain deeper insights into model selection, housing strategies, and study design that can accelerate your research pipeline, watch the full on-demand webinar today. View now to access expert guidance and real-world case studies designed to help you get the most from your DIO and MASH studies.