A reciprocal interaction between food-motivated behavior and diet-induced obesity

Abstract

Objectives: One of the main causes of obesity is overconsumption of diets high in fat and sugar. We studied the metabolic changes and food-motivated behavior when rats were subjected to a choice diet with chow, lard and a 30% sucrose solution (high fat high sugar (HFHS)-choice diet). Because rats showed considerable variations in the feeding response to HFHS-choice diet and in food-motivated behavior, we investigated whether the motivation to obtain a sucrose reward correlated with the development of obesity when rats were subsequently subjected to HFHS-choice diet. Method: We first studied feeding, locomotor activity and body temperature, fat weights and hormonal concentrations when male Wistar rats were subjected to HFHS-choice diet for 1 week. Second, we studied sucrose-motivated behavior, using a progressive ratio (PR) schedule of reinforcement in rats that were subjected to the HFHS-choice diet for at least 2 weeks, compared to control rats on a chow diet. Third, we measured motivation for sucrose under a PR schedule of reinforcement in rats that were subsequently subjected to HFHS-choice diet or a chow diet for 4 weeks. Fat weights were measured and correlated with the motivation to obtain sucrose pellets. Results: One week on the HFHS-choice diet increased plasma concentrations of glucose and leptin, increased fat stores, but did not alter body temperature or locomotor activity. Moreover, consuming the HFHS-choice diet for several weeks increased the motivation to work for sucrose pellets. Furthermore, the motivation to obtain sucrose pellets correlated positively with abdominal fat stores in rats subsequently subjected to the HFHS-choice diet, whereas this correlation was not found in rats fed on a chow diet. Conclusion: Our data suggest that the motivation to respond for palatable food correlates with obesity due to an obesogenic environment. Conversely, the HFHS-choice diet, which results in obesity, also increased the motivation to work for sucrose. Thus, being motivated to work for sucrose results in obesity, which, in turn, increases food-motivated behavior, resulting in a vicious circle of food motivation and obesity. IntroductionObesity is one of the fastest growing medical problems in modern society. It contributes to the development of chronic disorders such as cardiovascular disease, type 2 diabetes, hypertension and some cancers. 1 For healthy body weight regulation, it is important to balance energy intake and energy expenditure. Modern society, however, is characterized by a sedentary lifestyle and a calorie intake, which is not adjusted for that. Although regulatory mechanisms that balance intake and expenditure are known , 2,3 it still remains unclear why this fails in obese individuals. It has been postulated that the ability to overconsume high-energy dense foods (in the face of plentiful food availability) was selected during evolution. Thus, under conditions when food availability is uncertain and scarce, consuming highenergy dense foods is an adequate adaptation (for a review see Uli...

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