Nicolas Gausserès

Protein is more potent than carbohydrate for reducing appetite in rats.

The purpose of this study was to characterize further the effects of loads of protein versus carbohydrate on subsequent food intake in rats. We used an intraoral cannula to deliver isoenergetic isovolumic loads, in a tightly controlled time frame allowing for both metabolic responses and orosensory components of the load. Our results showed that the gluten load (GLT-100%) induced a greater depression in food intake than an isocaloric wheat starch load (GLT-0%). The types of protein used in the load (total milk protein vs. GLT) did not seem to influence their appetite-suppressive effect. There was a dose-dependent effect of the satiating effects of the protein loads, the GLT-100% load being more effective than either the GLT-35% or GLT-50% loads. Pattern analysis of the meal following the load suggested that animals were more satiated by protein, at least when loads contained 35% or 50% of protein, than by carbohydrate. At least 1 day was necessary before we saw a significant decrease in the energy intake following the protein loads. Thus, the animals had to learn the postingestive effects of the loads before the response stabilized. Taken together, the present results confirm that protein has a greater satiating effect than carbohydrate and extend these results by revealing that the larger the proportion of protein in the food, the larger the satiating effect, and that the quality of protein does not seem to play a significant role.

mTOR, AMPK, and GCN2 coordinate the adaptation of hepatic energy metabolic pathways in response to protein intake in the rat.

Three transduction pathways are involved in amino acid (AA) sensing in liver: mammalian target of rapamycin (mTOR), AMP-activated protein kinase (AMPK), and general control nondepressible kinase 2 (GCN2). However, no study has investigated the involvement of these signaling pathways in hepatic AA sensing. To address the question of liver AA sensing and signaling in response to a high-protein (HP) dietary supply, we investigated the changes in the phosphorylation state of hepatic mTOR (p-mTOR), AMPKalpha (p-AMPKalpha), and GCN2 (p-GCN2) by Western blotting. In rats fed a HP diet for 14 days, the hepatic p-AMPKalpha and p-GCN2 were lower (P < 0.001), and those of both the p-mTOR and eukaryotic initiation factor 4E-binding protein-1 phosphorylation (p-4E-BP1) were higher (P < 0.01) compared with rats receiving a normal protein (NP) diet. In hepatocytes in primary culture, high AA concentration decreased AMPKalpha phosphorylation whether insulin was present or not (P < 0.01). Either AAs or insulin can stimulate p-mTOR, but this is not sufficient for 4E-BP1 phosphorylation that requires both (P < 0.01). As expected, branched-chain AAs (BCAA) or leucine stimulated the phosphorylation of mTOR, but both insulin and BCAA or leucine are required for 4E-BP1 phosphorylation. GCN2 phosphorylation was reduced by both AAs and insulin(P < 0.01), suggesting for the first time that the translation inhibitor GCN2 senses not only the AA deficiency but also the AA increase in the liver. The present findings demonstrate that AAs and insulin exert a coordinated action on translation and involved mTOR, AMPK, and GCN2 transduction pathways.

Consequence of Omitting or Adding a Meal in Man on Body Composition, Food Intake, and Metabolism

Objective: To investigate in man the consequence on body composition and related biological and metabolic parameters of omitting or adding a meal.

The gastro-ileal digestion of 15N-labelled pea nitrogen in adult humans.

The aim of the present study was to determine the gastro-ileal behaviour of pea protein in humans. For this purpose, twelve healthy volunteers were intubated with an intestinal tube located either in the jejunum (n 5) or in the ileum (n 7). After fasting overnight, they ingested 195 mmol N of [15N]pea. Intestinal samples were collected for 6 h in the jejunum and for 8 h in the ileum. Before meal ingestion the basal liquid flow rate (ml/min) was 2.01 (SD 0.31) in the jejunum and 2.02 (SD 0.33) in the ileum. After meal ingestion the liquid phase of the meal peaked in the 40-60 min period in the jejunum and in the 150-180 min period in the ileum. The jejuno-ileal transit time of the liquid phase of the meal was 102 min. The basal flow rate of endogenous N (mmol N/min) was 0.22 (SD 0.15) in the jejunum and 0.16 (SD 0.10) in the ileum. The endogenous N flow rate peaked significantly (P < 0.05) in the jejunum in the 40-60 min period whereas no stimulation of endogenous N could be detected in the ileum after meal ingestion. A significantly increased (P < 0.05) concentration of exogenous N was detected in the jejunum during the 20-320 min period and during the 90-480 min period in the ileum. The overall true gastro-ileal absorption of pea N was 89.4 (SD 1.1)% with 69 (SD 14)% absorbed between the stomach and the proximal jejunum and 20.4% between the proximal jejunum and the terminal ileum. The percentage of ethanol-insoluble fraction (PN) in the exogenous N at the terminal ileum increased significantly (P < 0.05) to 75% after 360 min. These results suggest that heat-treated pea protein has a digestibility close to that of animal protein.

A role for glucose and insulin preprandial profiles to differentiate meals and snacks.

A physiological distinction between eating occasions may help account for contradictory findings on the role of eating frequency in energy homeostasis. We assessed this issue using a midafternoon eating occasion known in France as the goûter that often consists of snack foods. Among the 24 male subjects, 8 habitually consumed four meals per day, i.e., were usual goûter eaters (GE) and 16 habitually took 3 meals per day, i.e., usual non-goûter non-snack eaters (NGNSE). All subjects were time blinded from lunchtime and had to request subsequent meals. Blood was continuously withdrawn and collected with a change of tube every 10 min until dinner request. During the session, 8 of the non-goûter eaters (NGE) were offered a snack 210 min after lunch and were designated as non-goûter snack eaters (NGSE) if they ate. Results showed that the goûter was preceded by high hunger scores and a linear decline in plasma glucose (-9.0+/-3.0%, P<.05) and insulin concentrations (-22.9+/-6.0%, P<.05). These profiles were not observed before the snack. The dinner of GE was requested later and was smaller compared to NGNSE, whereas the snack altered neither time of request nor energy intake (EI) at dinner. Among blood variables, leptin at the onset of eating was the only factor that was predictive of both intermeal interval and EI. The glucose and insulin profiles indicate that snacks should not be considered as meals in studies on the role of eating frequency in energy homeostasis.

Whole-body protein turnover in humans fed a soy protein-rich vegetable diet

Objectives: This study was designed to compare the whole-body protein turnover in humans after the ingestion of a soy protein-rich vegetable diet with that of a control group fed a western animal protein-rich diet. Subjects: Twelve male volunteers were divided into two groups of six subjects who were given for two weeks either a 85% vegetable protein diet (diet VP) or a control western animal protein-rich diet (diet AP). Interventions: Whole-body protein turnover was estimated at the end of the two-week controlled diet period using the [15N]-glycine end-product method. Nitrogen flux rates were determined in the fed state (1.3 g protein/kg) over a 9 h period after the dose of [15N]-glycine was given. Results: After the 9 h of the test, the urinary ammonia excretion was significantly higher in the group receiving the diet AP than that in the group receiving the diet VP (P<0.05). In contrast, there was no significant difference for both total nitrogen and urea nitrogen excretions. Both the protein synthesis and the protein breakdown were similar in both groups. In the same way, the net protein deposition measured in the fed state during 9 h was similar for both diets at 0.07 g/kg/h. Conclusions: Young adults fed 1.3 g/kg/d of either meat or vegetable protein-rich diet for two weeks did not show a different protein turnover. Sponsorship: This work was supported in part by grant from Eridania Béghin-Say Compagny.

Absorption and metabolic distribution of [ 15 N]-Labeled Pea Nitrogen in Humans

Postprandial [15N]-labeled pea protein absorption and exogenous nitrogen retention were evaluated in humans. The true gastro-ileal absorption of pea protein was 89.4 ± 1.1%, and pea nitrogen retention represented 78% of the absorbed dietary nitrogen. These results demonstrate the good true nitrogen digestibility and retention of pea protein in humans.