The high-fat diet known as D12492 (60 kcal% fat) has become globally recognized as the gold standard for inducing obesity in rodents. This article explores the widespread use, benefits, and considerations associated with the D12492 diet in research.
Introduction to D12492
Since 1999, the D12492 diet has been instrumental in helping researchers understand the mechanisms and consequences of obesity. Its consistent formulation ensures that results are reproducible across different studies and laboratories, contributing to its status as the gold standard. The cumulative body of data in rodents fed D12492 is a powerful database for the scientific community, allowing researchers to compare results and plan future experiments.
The Rise of D12492 in Obesity Research
D12492 began as a custom diet order for one customer in 1999. The data demonstrates its widespread, continuous and increasing use, reflecting its importance and reliability in obesity research. Given the recent developments in the pharmaceutical treatment of obesity, we expect that the use of diets like D12492 will continue to grow.
Advantages of Using D12492
- Reproducibility: The consistent formulation of D12492 ensures that results are reproducible across different studies and laboratories.
- Established Standard: D12492 is globally recognized as the gold standard for inducing obesity in rodents.
- Extensive Data: The cumulative body of data in rodents fed D12492 is a powerful database for the scientific community, allowing researchers to compare results and plan future experiments.
- Customization: Hundreds of modifications can be made to these formulas to meet individual researcher needs.
- Availability: These custom diets are kept in-stock in pelleted form and ready for shipment. All our in-stock diets can be irradiated.
Choosing the Right Diet: Key Considerations
When choosing a control diet, one should ask three questions:
- Can I report it (can I tell others exactly what my animals were fed)?
- Can I repeat it (is there diet variability and will I be able to get the same results next year)?
- Can I revise it (as my hypotheses change, can I easily change the dietary components while keeping it otherwise matched to previous diets)?
The answer should be “yes” to all three.
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Important Considerations for VHFD Quality and Animal Welfare
Researchers are obligated to ensure food quality and provide laboratory animals with a palatable diet. Factors influencing the quality and palatability of very high-fat diet (VHFD), a widely used rodent diet, however, are understudied.
Storage and handling practices of VHFD are important because they can impact experimental outcomes. The temperature at which VHFD is stored, for example, differentially alters weight gain and liver damage in mice. Storage conditions of VHFD also affect pulmonary inflammation in mice. How storage and handling conditions of VHFD impact experimental outcome could be related to food quality.
Mitigating Dehydration and Oxidation of VHFD
Mitigating dehydration and oxidation of VHFD by replacing food daily, rather than weekly, stabilized feeding behavior without effect on overall cardio-metabolic health. Importantly, daily replacement of VHFD also reduced measures of anxiety-like behavior in the open field test. Refining husbandry practices to include daily replacement of VHFD can therefore ensure VHFD quality and improve animal welfare.
Daily Replacement of VHFD Stabilizes Food Intake and Improves Mouse Welfare
Dr. Cordeira first established a baseline of the daily food intake within a one-week period and determined the palatability of D12492 by conducting food preference testing and measuring the dopamine release. Following that, he studied how palatability was affected by pellets that were either dehydrated or oxidized. The results revealed a notable variation in D12492 intake throughout the week with weekly replacement leading to reduced palatability relative to more frequent changes.
The reduced food intake can be attributed to the diminished palatability of D12492 over the course of the week, due to reduced water content and increased lipid oxidation. The reduced palatability following the weekly replacement is due mainly to the oxidation status of D12492, not the water content or the act of replacing it.
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Subsequently, the author discovered that daily food replacement of freshly thawed D12492 can stabilize the food intake over the course of a week. Surprisingly, the cumulative intake over the 8-week feeding experiment period remained consistent between the two feeding schedules (i.e. daily change vs. no change over the week), due to a greater intake of the mice on day 1 after receiving fresh diet following one week compared to those that were receiving fresh food daily. In addition, phenotypes and other metabolic parameter readings from the two feeding regimes showed no significant difference.
Lastly, the author also advocated for the adoption of daily replacement of D12492 as it can help reduce stress and anxiety while promoting animal welfare.
Hyperphagia and Hypophagia in Mice Receiving Weekly Food Replacement
Dr. Cordeira reported only mice receiving weekly food replacement for 8-weeks exhibited hyperphagia following VHFD replacement (Mondays) and hypophagia following cage change (Fridays).
Recommendations for Storage and Handling of D12492
We recommend the researchers and vivarium technicians store D12492 frozen at -20 degrees C. Moreover, we typically recommend changing the diet at least twice a week, yet daily could be more preferable according to the paper and based on the user’s preference. When changing the diet, the old diet in hoppers/feeders should be removed and then replaced with fresh diet rather than just topping off the hoppers/feeders with new diet.
The Impact of High-Fat Diets on the Uterine Estrous Cycle of Nulligravid Mice
Both HFDs produced significant weight gain, with 60% HFD and 45% HFD gaining significant weight after 2 weeks and 15 weeks, respectively. Additionally, both HFDs led to glucose intolerance, fatty liver, and adipocyte hypertrophy. Mice fed 60% HFD displayed hyperphagia in the first 12 weeks of HFD treatment. Moreover, 60% HFD-treated mice had a longer estrous cycle length and an increased percentage of estrus stage samplings compared to CD-treated mice. Estrous cycle stage-controlled 60% HFD-treated mice displayed an increased estrogen-to-progesterone ratio and decreased ovarian corpora lutea compared to CD-treated mice, which may underlie the observed estrous cycle differences. There was no significant difference between diets regarding endometrial morphology or the percent of endometrial CD45+ immune cells.
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Experimental Design: Diet-Induced Obesity Study in Female C57BL/6J Mice
Four-week-old female C57BL/6J wild-type (WT) mice were purchased from The Jackson Laboratory (Strain #000664, Bar Harbor, ME, USA) and given 3 weeks to acclimate before initiating diets. In the first cohort of mice, 7-week-old mice were put on either a 60% HFD (Research Diets, D12492) or its respective 10% low-fat (7% sucrose-matched) CD (Research Diets, D12450J) or a 45% HFD (Research Diets, D12451) or its respective 10% low-fat (17% sucrose-matched) CD (Research Diets, D12450H). The second cohort of mice started diet treatments at 5 to 12 weeks of age and were only given either the 60% HFD or the 60% CD. Mice were fed ad libitum for 22 weeks in the first cohort and 30 to 37 weeks in the second cohort.
Monitoring Obesity Progression and Metabolic Disturbances
Currently, a few methods are available to monitor the progression of obesity and related metabolic disturbances (i.e. DIO phenotype), including elevated circulating leptin, insulin, lipids, and glucose intolerance.