Analyses of meal patterns across dietary shifts

Abstract

The direct controls of meal size can be categorized into positive signals such as those from the oral cavity and negative signals such as postoral inhibitory cues. It follows that the relative contribution of these signals, and in turn meal pattern parameters, change across periods of high-energy diet exposure. Here, we compared daily intake and meal pattern analysis in male Sprague-Dawley rats presented a high-energy diet for 6 weeks then standard chow for ~ 1 week (HE), with those of standard chow fed controls (CHOW). These measures allow for evaluation of 1) whether there are distinct dynamic and static phases of DIO and if so, how they are characterized, 2) how meal patterns change across short and long term HE experience, and 3) ingestive behavioral changes when HE-fed animals are returned to standard chow. The HE animals showed significantly higher intake primarily driven by an increase in meal size compared to CHOW controls. This was most pronounced during the first several days of high-energy diet exposure thus characterizing the dynamic phase. Intake and meal size decreased with longer exposure to the diet but remained significantly higher than those of CHOW. Increased meal size could be driven by enhanced orosensory stimulation and/or reduced sensitivity to postoral inhibitory feedback. Distribution curves derived from histogram plots of meal size revealed both larger average meal size (right shift) and spread (standard deviation) thus it is tempting to speculate that more than one type of mechanism influences increased meal size. Meal number decreased suggesting post meal inhibitory signaling is relatively intact. However, this increase was insufficient to compensate for the increased meal size. When HE animals were switched to standard chow, daily intake and meal size decreased and eventually returned to values comparable to those of the CHOW rats. Meal number remained lower suggesting altered physiological mechanism(s) that underlie the control of ingestive behavior as a function of previous high-energy diet exposure.

Disruption of the light cycle ablates diurnal rhythms in gastric vagal afferent mechanosensitivity

“…The SCN responds to light, having direct neural connections with the retina, and under “normal” light‐dark cycles, there are 24‐hour rhythms in food intake and metabolism . Specifically, during the light phase rodents consume smaller meals and less often compared to the dark phase . Similar results were obtained in the current study in SLD‐NL mice.…”

Western diet and the weakening of the interoceptive stimulus control of appetitive behavior

“…Evidence for this learning has been obtained after as few as three reinforced trials [17], and discriminative control generalizes from cues produced by food deprivation and satiation to hormonal manipulations such as exogenous administration of ghrelin [23], cholecystokinin-octapeptide (CCK-8) [24, 25], and leptin [25] that are known to promote or suppress feeding behavior. Experiment 1 expanded on these earlier studies by employing levels of food deprivation and satiation more comparable to what rats would experience as part of their normal meal patterning (i.e., 0 and 4h food deprivation) (e.g., [26]). Experiment 2 investigated (a) how cues arising from low levels of food deprivation control appetitive behavior in compound with discrete external cues, and (b) how consuming a Western diet affects discriminative control by food deprivation cues in the presence and absence of external stimuli.…”

Alterations in sucrose sham-feeding intake as a function of diet-exposure in rats maintained on calorically dense diets

“…Daily intake and meal size decreased and eventually returned to values comparable to chow-fed controls. Meal number remained lower suggesting exposure to the calorically dense diet elicited changes in physiological mechanism(s) that underlie ingestive behavior control (Treesukosol and Moran, 2013a). …”

“…The 45% high-fat diet contains a fat content comparable to that of western diets in human populations (Drewnowski and Popkin, 1997). The diet does not include a liquid component and was used in our previously reported meal pattern analysis study (Treesukosol and Moran, 2013a). We hypothesized that enhanced orosensory stimulation elicited by exposure to the calorically dense diets would generalize to increased responsiveness to other palatable stimuli such that sham-feeding intake of sucrose should be higher in HE and HF animals compared to intake in CHOW controls.…”