Consummatory, anxiety-related and metabolic adaptations in female rats with alternating access to preferred food

Abstract

Avoidance of and relapse to palatable foods is a qualitative aspect of dieting, a putative risk factor for eating disorders or obesity. The present studies tested the hypotheses that rats with alternating access to highly preferred foods would show: (1) hypophagia, a function of the relative hedonic value of the underaccepted diet, (2) increased anxiety-like behavior and psychomotor arousal when preferred diet was unavailable, (3) obesity-like changes, and (4) stable individual differences in diet-switch-induced hypophagia. Preferences among three high-carbohydrate diets were determined in female Wistar rats (n=16). Adolescent rats (n=162) received the following weekly diet schedules: (1) continuous regular chow (7 days/week), (2) chow (5 days/week) followed by a more preferred diet (2 days/week), or (3) chow (5 days/week) followed by a less preferred chow (2 days/week). Some animals were yoke-restricted (75% calories) when provided chow to increase its rewarding properties. Diurnal locomotor activity was measured in a familiar environment, and anxiety-like behavior was assessed in the elevated plus-maze and defensive withdrawal tests. Rats withdrawn from the preferred diet showed hypophagia, anxiogenic-like behavior, increased locomotion, and weight loss. Chow hypophagia was progressive, individual-specific in magnitude, (partly) non-homeostatic in nature, and blunted by previous chow restriction. Despite eating less, rats cycled with the preferred diet became heavier, fatter, and diurnally less active, with greater feed efficiency and proinflammatory adipokine levels than chow controls. The present diet cycling procedure may model consummatory, anxiety-related, and metabolic effects of qualitative dieting in humans.

Figure 1

Study design of Experiment 3.

Figure 2

Effects of repeated, alternating 5-day access to chow and 2-day access to either chow (Chow/Chow, n = 16) or highly preferred chocolate-flavored sugary diet (Chow/Preferred, n = 14) in female Wistar rats. Panels show (M ± S.E.M.) (A) average daily food intake, and (B) food intake of Chow/Preferred rats within C (Chow) and P (Preferred) diet phases relative to chow-fed controls. Symbols indicate significant differences (p < 0.05) from *Chow/Chow, ^&0, ^†C (Chow) phase of Week 2, ^€P (Preferred) phase of Week 2, or ^§respective C (Chow) phase.

Figure 3

Effects of repeated, alternating 5-day access to chow and 2-day access to either regular chow (Chow/Chow, n = 12) or a slightly less preferred chow (Chow/Non-Preferred, n = 8) in female Wistar rats. Panels show (M ± S.E.M.) (A) average daily food intake, and (B) food intake of Chow/Non-Preferred rats within C (Chow) and NP (Non-Preferred) diet phases relative to chow-fed controls. Symbols indicate significant differences (p < 0.05) from *Chow/Chow, ^&0, ^†C (Chow) phase of Week 2, or ^€NP (Non-Preferred) phase of Week 2, or ^§respective C (Chow) phase.

Figure 4

Effects of diet alternation with or without caloric restriction during chow access on “chow switch” intake, or chow intake after preferred diet access on Day 1 of each weekly cycle (see Figure 1). Letters denote significant difference (p < 0.05) of: (a) Chow-Ad lib/Preferred (n = 16) from all groups; (b) Chow-Restricted/Preferred (n = 16) from Chow-Ad lib/Chow (n = 14); (c) Chow-Restricted/Chow (n = 14) from Chow-Ad lib/Chow; (d) Chow-Restricted/Preferred from Chow-Restricted/Chow. Panels show M ± S.E.M.

Figure 5

Long-term effects of diet schedule on motor activity and anxiety-like behavior in female Wistar rats. Panels show (M ± S.E.M.) (A) 12-h diurnal motor activity, represented as percent of Chow/Chow beam breaks. Rats were tested on Days 1, 4 (C phase) and 6 (P phase) of experimental Week 10 (n = 6–8/group), (B) elevated plus-maze behavior (left) percent of total arm time directed towards the open arms (lower % open arm time signifies more anxiogenic-like behavior), and (right) number of closed arm entries, an index of locomotor activity. Rats were tested during Week 8, 5–9 h after switches from preferred diet (B → A phase) or from chow diet (A → B phase), in a between-subjects design (n = 8–16/group), or (C) time spent in the withdrawal chamber during the defensive withdrawal test. Rats were tested during Week 8, 5–10 h after switches from palatable diet to chow diet (B → A phase) (n = 5–16/group). In all studies, the phase-appropriate diet and water were available ad libitum. Symbols indicate significant differences (p < 0.05) from *Chow/Chow; ^#Chow/Preferred Day 1 motor activity.

Figure 6

Effects of repeated, alternating 5-day access to chow and 2-day access to either chow (Chow/Chow, n = 16) or highly preferred chocolate-flavored sugary diet (Chow/Preferred, n = 14) in female Wistar rats. Panels show (M ± S.E.M.) (A) (Top) average daily change in body weight, and (Bottom) feed efficiency (body weight change/energy intake) during each C (Chow) or P (Preferred) diet phase of each week, or (B) cumulative body weight gain (Top) and feed efficiency (Bottom). *Differs from Chow/Chow p *< 0.05.

Figure 7

Long-term effects of diet schedule on body composition. Panel shows (M ± S.E.M.) fat mass and fat-free dry mass of a random subset of female Wistar rats from Experiment 1 (n = 15). On Day 92, rats were fed chow diet only for 10 consecutive days to control for acute diet effects. On Day 102, overnight fasted rats were decapitated 2–5 h into the dark cycle. Stacked bars represent absolute weights, and inset numerals indicate percent of total carcass mass. *Both absolute and relative fat mass of Chow/Preferred rats differ from Chow/Chow rats, p < 0.05.