Assessing Food Choices after Gastric Bypass Using a Multi-Food Meal Pattern Monitor in a Rat Model

Animals must eat to attain essential nutrients and energy for survival. Diet -- the types and quantities of food consumed -- is clearly tied to the overall health of humans and other animals. So, too, is the way in which those foods are consumed. Most animals eat food in meals, discrete periods of time throughout the day. The study of the timing and size of meals, called meal pattern analysis, has been used for decades with rodent models to better understand the complex interactions between feeding behaviors, health status, and the physiological, endocrine, and neural factors involved in the control of food intake. While most of the published studies are based on the measurement of a single food or fluid, it is also known that the availability of food choices influences behavior and overall health, leading to hyperphagia, rapid increases in body weight and fat mass, altered gene expression, and changes in stress responses, motivational behaviors, and also the way that animals consume food. The knowledge that the food environment influences behavior has led to the increased use of a cafeteria diet paradigm, providing several human foodstuffs across time, in rodent models of eating and drinking relevant to human health. Ultimately, the ability to measure and describe the meal patterns associated with intake of and choices between multiple food options brings rodent models closer to emulating the food environment of humans. To that end, Chapter 2 describes a new device for rats: the 5-Item Food Choice Monitor (FCM). The FCM continuously records intake from up to 5 foods and 2 fluids simultaneously. The remainder of Chapter 2 is given to considerations necessary for the development of software to compile intake into meals, and how data collected for the purpose of validating the reliability of the FCM correspond with previous studies using fewer (or no) food choices. Overall, these data related well to previous studies, providing confidence that the FCM and software are both appropriate for meal pattern analysis. Chapter 3 describes the application of the FCM and the cafeteria diet paradigm to the study of meal patterns and food choices after Roux-en-Y gastric bypass (RYGB) surgery using a rat model. RYGB is a bariatric surgery used to reduce obesity and its comorbidities in humans. The success of the surgery is primarily attributed to sustained weight loss via reduced caloric intake, and there are also reports that patients specifically decrease intake of foods high in sugar and/or fat. However, there has been little direct measurement of food intake and choices by postoperative patients, and what little data exist do not provide evidence of a selective decrease in the types of foods consumed, only the quantity. Rodent models of bariatric surgery have been used with success to study the physiological and behavioral changes associated with the surgery, and in general these models correspond well with patient data. These studies typically show that rats and mice will decrease caloric intake by reducing consumption of foods and fluids high in fat and sugar, and alter food choices to increase intake of foods of lower caloric density. Decreased intake is associated with animals consuming smaller meals. However, whether reduced caloric consumption and altered food choices after RYGB surgery is directly tied to reduced meal sizes has not been explicitly tested using a complex, multi-food design. Here, female rats were provided with powdered chow and then a cafeteria diet in the FCM both before and after surgery. RYGB rats displayed hyperphagia in the first meal consumed upon access to the cafeteria diet and did not differ from the control group, indicating that after surgery the animals were still motivated to consume these foods. Thereafter, however, the meal size of the RYGB rats dropped precipitously leading to reduced intake relative to the control group throughout the cafeteria diet testing. suggesting that RYGB rats rapidly learned to associate the foods with new postingestive consequences of consuming them as a result of the surgery. RYGB rats also reduced the rate at which calories were consumed in a meal (eating rate) and, despite initiating a similar number of meals as before surgery, consumed more of those meals while lights were on, when the nocturnal rats would normally be dormant. Together, these results indicate that RYGB rats modify feeding patterns to more evenly spread caloric consumption across the day, possibly to avoid negative postingestive feedback from eating foods high in sugar or fat. While meal patterns changed quickly, food choices were altered more slowly across days, suggesting that behavioral modifications to meal patterns and food choices are related to different processes after the surgery. These studies represent the first use of meal pattern analysis together with a cafeteria diet paradigm that more closely emulates the typical human experience. While many of the results were consistent with those from studies using a single food item, the use of several foods simultaneously also allows observation of how self-selected diets impact the way food is consumed, how food choices and macronutrient intake are regulated, and can ultimately provide information about the interaction between these behaviors are affecting the overall physiology and nutrition of the animal.