Acute exposure to a high-fat diet alters meal patterns and body composition
Introduction
Overweight and obesity are chronic global health issues [1], [2] associated with heart disease, diabetes, fatty liver, kidney disease, certain cancers, disability and mortality [3]. The increased incidence of obesity is often attributed to increased intake of dietary fats and decreased energy expenditure [1], [4].
Like humans, rodents also show a preference for high-fat (HF) diet [5], [6] resulting in similar metabolic consequences [4]. Specifically, rats with access to HF diet defend a higher body weight [7] and continue to over-consume HF diet even when palatability and energy density are kept constant [8]. This indicates that HF diet has orosensory and palatability characteristics as well as postingestive effects that contribute to overconsumption which, in turn, lead to increased weight gain and adiposity [9], [10].
However, the way in which foods are consumed, or their pattern of consumption, also has implications on body weight and composition [11]. For example, consuming many small meals throughout the day decreases body weight relative to consuming the same number of calories in a few large meals [12], whereas reducing meal frequency by as little as one meal per day has been shown to increase body adiposity [13]. Meal patterns are affected by a variety of physiological and environmental factors including food deprivation or restriction [14], [15], eating disorders [16], stress [17], [18], pharmacological treatments [19], [20], exercise [14], [21], social situations [22], [23], time of day [24], [25], macronutrients [25], [26], and hormones [27], [28]. The pattern of consumption ultimately determines total caloric intake; thus, examination of feeding behavior on a meal-to-meal basis provides insight into the microstructure of food intake, which can specifically determine the characteristics of ingestive behavior that influence changes in physiology. For example, prior to the development of obesity and as early as 2 days of age OLETF rats, which lack cholecystokinin-1 receptors, consume larger meals. Similarly, outbred diet-induced obese (DIO) rats display disrupted feeding patterns in the preobese state [21], [29], [30]. These animal models of obesity as well as normal-weight rats will take larger meals when given limited access to HF diet [24], [31], [32]. This suggests that taking larger meals promotes the gain of adipose tissue, but also that exposure to a HF diet provokes the taking of larger meals that may contribute to the development and/or maintenance of increased body weight and obesity. Previous studies of meal patterns and dietary manipulations have included diets of different forms (liquid, snacks, and pellets), short exposure periods, the use of multiple testing apparatuses, and animals known to be prone to obesity [32], [33], [34], [35], [36], [37] however, few have examined the meal patterns of normal-weight, non-genetically altered animals presented with continuous access to HF diet to determine how ingestive behavior changes relate to the gain of body weight and adipose tissue.
The current study assessed the development of meal pattern differences in normal-weight rats fed a HF or chow diet ad libitum over a nine-day period to test the hypothesis that access to HF diet alters the pattern of feeding, with HF fed animals consistently consuming larger meals than chow fed conspecifics, and that these animals, not known to be prone to obesity, would gain more weight and adipose tissue.
Section snippets
Animals
Ninety-day old male Long–Evans rats (Harlan; Indianapolis, IN) were individually housed in DietMax-ID monitoring cages (#45-DMCD2R, Accuscan Instruments; Columbus, OH). The animal room was temperature- and humidity-controlled on a 12-h light:dark cycle. Animals were maintained in accordance with the Guide for the Care and Use of Laboratory Animals [38]. All protocols, animal handling and treatment were approved by the Institutional Animal Care and Use Committee at the University of Cincinnati.
Results
Exposure to HF diet resulted in both weight gain and body composition changes. Animals fed the HF diet began to gain more weight than chow fed controls by day 5 and the difference reached statistical significance on day 9 (t(8) = 2.457, p < 0.04) (Fig. 1A). During exposure to the HF diet animals gained more adipose tissue than chow fed controls (t(8) = 5.275, p < 0.001). Both groups gained lean tissue and there was no statistical difference between groups in this measure (Fig. 1 B and C).
Animals
Discussion
The present study characterized the changes in meal patterns that occur during continuous access to HF diet in normal-weight rats and related the possible differences in ingestive behavior to changes in body weight and composition. Consistent with previous studies, animals fed a HF diet consumed more calories via larger, yet fewer, meals [24], [40], [41], [42]. Furthermore, despite only an acute exposure to the HF diet (9 days), these animals gained more weight and adipose tissue than chow fed
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