Palatable Western-style Cafeteria Diet as a Reliable Method for Modeling Diet-induced Obesity in Rodents

Summary

This protocol describes the use of a highly palatable, western-style cafeteria diet to model overeating and obesity in rodents. Here, we provide a detailed outline of food selection, preparation and measurement, and explain methodological factors that assist in generating a robust and reproducible phenotype.

Abstract

Obesity is rapidly increasing in incidence in developed and developing countries and is known to induce or exacerbate many diseases. The health burden of obesity and its comorbid conditions highlight the need for better understanding of its pathogenesis, yet ethical constraints limit studies in humans. To this end externally valid models of obesity in laboratory animals are essential for the understanding of being overweight and obesity. While many species have been used to model the range of changes that accompany obesity in humans, rodents are most commonly used. Our laboratory has developed a western-style cafeteria diet that consistently leads to considerable weight gain and markers of metabolic disease in rodents. The diet exposes rodents to a variety of highly palatable foods to induce hyperphagia, modeling the modern western food environment. This diet rapidly induces weight gain and body fat accumulation in rats allowing for the study of effects of overeating and obesity. While the cafeteria diet may not provide the same control over macronutrient and micronutrient profile as purified high-fat or high-fat, high-sugar diets, the cafeteria diet typically induces a more severe metabolic phenotype than that observed with purified diets and is more in line with metabolic disturbances observed in the overweight and obese human population.

Introduction

Obesity and its related comorbidities make an enormous contribution to global health burden¹ and account for 7% of disease burden in Australia². A leading risk factor for obesity is consumption of unhealthy diets that are high in saturated fat and refined carbohydrates, and low in fiber and micronutrients³. Identifying targets for therapeutic intervention for obesity requires models that can systematically assess effects on multiple biochemical and physiological systems. Our understanding of the etiology of obesity has been advanced substantially by work using rodent models, where behavioral, meta....

Protocol

The protocol described here has been optimized for use in rats. While we have used the CAF diet successfully in mice^17,18, soft food grinding may introduce further error reducing the reliability of food intake measures¹⁹. This protocol is approved by the Animal Care and Ethics Committee at the University of New South Wales and complies with the Australian guidelines for the use and care of animals for scientific purposes (8th Edition) provided by the Australian National Health and Medical Research Council.

NOTE: Very few adverse effects have ....

Results

As shown in Figure 2A, CAF diet feeding produces a 2.5-fold increase in energy intake relative to chow controls, based on data from three cohorts of male Sprague Dawley rats, that is consistent over 6 weeks. Other studies have confirmed that this extent of hyperphagia is sustained over 10²¹ and 16²² week experiments. The weight curve (Figure 2B) indicates CAF diet feeding leads to .......

Discussion

By exposing rats to a variety of highly palatable foods high in fat and sugar, the CAF diet protocol described here provides a reliable and robust model of the so-called ‘western diet’ eaten by many people. Hyperphagia—assessed as a significant increase in energy intake relative to controls—is observed within the first 24 h of exposure, with statistically significant body weight differences seen within weeks. Thus, CAF is an effective model of diet-induced obesity for rodents.

Materials

Name	Company	Catalog Number	Comments
2-5 L plastic bottle			For preparing 10% sucrose solution, if applicable
Chopping board			Plastic is advised
Freezer			For storing CAF foods
Gordon's maintenance rodent chow	Gordon's Specialty Stockfeeds (Australia)		Maintenance diet used in our laboratory (14 kJ/g; 65% carb, 13% fat and 22% protein, as energy)
Large plastic storage boxes			All items above can be stored in containers for easy access
Large spoon			For CAF diet preparation
Microwave			For CAF diet thawing (when required)
Non-serrated knife			For CAF diet preparation
Paper towel			Important for cleaning work surfaces and the knife during CAF prep
Plastic containers			These are for weighing CAF food items on measurement days
Plastic funnel			For preparing 10% sucrose solution, if applicable
Red light			As CAF diet should be refreshed near the onset of the dark phase each day, a red light will assist when working in the dark
Tuna tins			For presenting 'wetter' CAF food items. Plastic containers may also be suitable
Weigh container x 3			Separate containers should be used to weigh rats, chow & bottles, and CAF foods
Weighing scale			Sensitivity to 0.1g is recommended
White sugar			For 10% sucrose solution, if applicable