Elsevier

Physiology & Behavior

Volume 90, Issue 4, 16 March 2007, Pages 664-668
Physiology & Behavior

Does intestinal absorption participate in the ponderostat?

https://doi.org/10.1016/j.physbeh.2006.12.004Get rights and content

Abstract

Body weight regulation is known to achieve energy balance through several responses: appetite, satiety, thermogenesis, feeding behavior. Absorption efficiency might be, also, another response. In this paper, we hypothesized that the intestinal absorption efficiency of the rat might be lowered in response to a high energy content of the diet. Thirty-one rats were assigned to a specific diet (restricted, control, and cafeteria) during three weeks. Rats' body mass, BMI, and body fat were measured and absorption efficiency was calculated through the ratio of energy ingested/energy defecated. Intestinal histology was examined post-mortem. Absorption efficiency was not lower in cafeteria groups but was higher than in control and restricted rats. No histological difference was seen after the various diets. Such results indicate that intestinal absorption is working at full efficiency whatever the diet, and is not a regulatory response contributing to the ponderostat.

Introduction

Since the works of Kennedy [1] and Hervey [2], body weight regulation is known to achieve energy balance through several responses: appetite, satiety, thermogenesis, feeding behavior. The main regulatory response is, of course, food intake. A deficit in energy balance raises food intake, and, inversely, an exceeding energy balance decreases it [3], [4]. The pleasure associated to food participates in that mechanism [5], [6]. Also, thermogenesis is adjusted in order to sustain energy balance [7], [8], [9]. Finally, rats' food hoarding, an anticipatory response that is proportional to a body weight deficit, also confirms the existence of such a ponderostat [10], [11], [12]. It seems, thus, that every mechanism that may affect energy balance is under the control of the body weight regulation.

Absorption efficiency might be another of those responses. Food intake is only the entry of nutrients into the digestive tract. The intestinal wall is the actual point where nutrients pass from the outside to the milieu intérieur. The amount of food entering the digestive system is controlled via appetite and satiety, but the intestinal absorption might be another good “control point” for the entering energy. One may expect that in time of energy need, the intestinal wall should become more efficacious and should absorb more energy from the intestinal chyme. Reciprocally one may expect that in fat subjects the intestinal absorptive capacity could decrease.

The present work was designed to assess the hypothesis that body weight regulation controls intestinal absorption efficiency to cope with body weight gain or loss.

Section snippets

Animals

Thirty-one 3 month-old males Wistar rats (Charles River, Montreal, QC, Canada), weighing 350–400 g at the beginning of the study were kept in animal quarters maintained at 22 °C with a 12:12-h dark–light schedule. Rats were housed individually in metal mesh-floored cages in order to facilitate feces and leftover food collection. Rats had a permanent access to fresh water. Animals were separated in four groups, and assigned to a specific diet for 3 weeks:

  • Group A (restricted): 25 g/d of Rodent

Food intake

According to their diet, rats ingested different amounts of food and of energy. Before the beginning of the specific diets, the mean energy intake of all groups was similar (P = 0.23). Over the 3-week diet, the mean ingested energy of restricted rats was lower than that of controls, and that of cafeteria groups was higher than that of controls (P < 0.001; Fig. 1).

Feces

Three weeks on specific diet influenced the mass of the feces and their energy content. At the end of the 3 weeks, mean mass of the

Discussion

The effectiveness of the different diets to affect body composition was shown by the changes in body weight, BMI, and body fat. Fig. 3 shows that indeed restricted diet lowered and cafeteria diet raised all the measured variables. Thus, the various diets were efficacious.

Comparing absolute amounts of energy defecated to amounts of energy ingested shows that the differences between groups in fecal energy were quantitatively marginal. In all groups, energy defecated was less than 0.25% of the

Acknowledgments

We thank Dr Pierre Samson for technical support. This work was supported by the Natural Sciences Research Council (NSRC) of Canada and by the Centre de recherche sur le métabolisme énergétique (CREME).

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