Altered feeding patterns in rats exposed to a palatable cafeteria diet: increased snacking and its implications for development of obesity.

BACKGROUND: Rats prefer energy-rich foods over chow and eat them to excess. The pattern of eating elicited by this diet is unknown. We used the behavioral satiety sequence to classify an eating bout as a meal or snack and compared the eating patterns of rats fed an energy rich cafeteria diet or chow. METHODS: Eight week old male Sprague Dawley rats were exposed to lab chow or an energy-rich cafeteria diet (plus chow) for 16 weeks. After 5, 10 and 15 weeks, home-cage overnight feeding behavior was recorded. Eating followed by grooming then resting or sleeping was classified as a meal; whereas eating not followed by the full sequence was classified as a snack. Numbers of meals and snacks, their duration, and waiting times between feeding bouts were compared between the two conditions. RESULTS: Cafeteria-fed rats ate more protein, fat and carbohydrate, consistently ingesting double the energy of chow-fed rats, and were significantly heavier by week 4. Cafeteria-fed rats tended to take multiple snacks between meals and ate fewer meals than chow-fed rats. They also ate more snacks at 5 weeks, were less effective at compensating for snacking by reducing meals, and the number of snacks in the majority of the cafeteria-fed rats was positively related to terminal body weights. CONCLUSIONS: Exposure to a palatable diet had long-term effects on feeding patterns. Rats became overweight because they initially ate more frequently and ultimately ate more of foods with higher energy density. The early increased snacking in young cafeteria-fed rats may represent the establishment of eating habits that promote weight gain

Rats eat a cafeteria-style diet to excess but eat smaller amounts and less frequently when tested with chow.

BACKGROUND: Obesity is associated with excessive consumption of palatable, energy dense foods. The present study used an animal model to examine feeding patterns during exposure to and withdrawal from these foods. METHODS: Male Sprague Dawley rats were exposed to standard lab chow only (Chow rats) or a range of cafeteria-style foods eaten by people (Caf rats). After 1, 4, 7 and 10 weeks of diet in their home cage, rats were subjected to 24-hour test sessions in a Comprehensive Lab Animal Monitoring System (CLAMS). In the first two test sessions, Chow rats were exposed to standard lab chow only while Caf rats were exposed to a biscuit and high-fat chow diet. In the final two test sessions, half the rats in each group were switched to the opposing diet. In each session we recorded numbers of bouts, energy consumed per bout, and intervals between bouts across the entire 24 hours. RESULTS: Relative to Chow rats, Caf rats initiated fewer bouts but consumed more energy per bout; however, their motivation to feed in the CLAMS declined over time, which was attributed to reduced variety of foods relative to their home cage diet. This decline in motivation was especially pronounced among Caf rats switched from the palatable CLAMS diet to standard lab chow only: the reduced energy intake in this group was due to a modest decline in bout frequency and a dramatic decline in bout size. CONCLUSIONS: Exposure to a cafeteria-diet, rich in variety, altered feeding patterns, reduced rats' motivation to consume palatable foods in the absence of variety, and further diminished motivation to feed when palatable foods were withdrawn and replaced with chow. Hence, variety is a key factor in driving excessive consumption of energy dense foods, and therefore, excessive weight gain

Switching from Sugar- to Artificially-Sweetened Beverages: A 12-Week Trial

Background: Consumption of sugar-sweetened beverages (SSBs) forms the primary source of added sugar intake and can increase the risk of metabolic disease. Evidence from studies in humans and rodents also indicates that consumption of SSBs can impair performance on cognitive tests, but that removing SSB access can ameliorate these effects. Methods: The present study used an unblinded 3-group parallel design to assess the effects of a 12-week intervention in which young healthy adults (mean age = 22.85, SD = 3.89; mean BMI: 23.2, SD = 3.6) who regularly consumed SSBs were instructed to replace SSB intake with artificially-sweetened beverages (n = 28) or water (n = 25), or (c) to continue SSB intake (n = 27). Results: No significant group differences were observed in short-term verbal memory on the Logical Memory test or the ratio of waist circumference to height (primary outcomes), nor in secondary measures of effect, impulsivity, adiposity, or glucose tolerance. One notable change was a significant reduction in liking for strong sucrose solutions in participants who switched to water. Switching from SSBs to ‘diet’ drinks or water had no detectable impact on cognitive or metabolic health over the relatively short time frame studied here. This study was prospectively registered with the Australian New Zealand Clinical Trials Registry (ACTRN12615001004550; Universal Trial Number: U1111-1170-4543)

Cafeteria-fed rats consumed more food and energy, and weighed more than chow-fed rats.

<p>Mean (±SEM) weekly 24 hr food intake in grams (left), energy intake in kilojoules (middle), and weekly body weight (right), in rats fed either standard lab chow (open circles) or a cafeteria (closed squares) diet for 16 weeks. Data were analyzed using repeated measures ANOVA (energy intake, n = 6 cages per group; body weight, n = 12).</p

Percentage snacking at 5 weeks correlated with terminal body weights of cafeteria-fed rats.

<p>Mean snack number plotted against mean percentage snacking (panel A), and terminal body weight plotted against mean percentage snacking (panel B) in chow (open circle) and cafeteria-fed (closed square) rats at 5 (left), 10 (middle) and 15 (right) weeks of diet. Outliers in the cafeteria-fed group (the three lightest rats in this group) were excluded from the analyses. Data were analyzed using correlation analysis.</p

Cafeteria-fed rats persistently consumed more fat, even when adjusted for body weight.

<p>Mean (±SEM) weekly macronutrient intake (protein, carbohydrate and fat) in kilojoules (panel A), and in kilojoules adjusted for body weight (panel B) in rats fed either standard lab chow (open circles) or a cafeteria (closed squares) diet for 16 weeks. Data were analyzed using repeated measures ANOVA (n = 6 cages per group).</p

Cafeteria-fed rats are more likely to eat consecutive snacks between meals.

<p>Mean relative frequency of different feeding sequences at 5 (left), 10 (middle) and 15 (right) weeks; panel A), S-S: snack followed by snack, S-M: snack followed by meal, M-S: meal followed by a snack, M-M: meal followed by a meal. Panel B shows mean (±SEM) intervals between elements of a sequence (e.g. the average interval between a snack followed by a snack) during the dark phase (7 pm–7 am) following 5 (left), 10 (middle), and 15 (right) weeks of diet, in chow (open bars) and cafeteria (closed bars) fed rats. Data were analyzed via the Chi-squared goodness of fit test (relative frequency of sequences) and repeated measures ANOVA (intervals within sequences).</p