Peripheral and central mechanisms involved in the control of food intake by dietary amino acids and proteins

Abstract

The present review summarises current knowledge and recent findings on the modulation of appetite by dietary protein, via both peripheral and central mechanisms. Of the three macronutrients, proteins are recognised as the strongest inhibitor of food intake. The well-recognised poor palatability of proteins is not the principal mechanism explaining the decrease in high-protein (HP) diet intake. Consumption of a HP diet does not induce conditioned food aversion, but rather experience-enhanced satiety. Amino acid consumption is detected by multiple and redundant mechanisms originating from visceral (during digestion) and metabolic (inter-prandial period) sources, recorded both directly and indirectly (mainly vagus-mediated) by the central nervous system (CNS). Peripherally, the satiating effect of dietary proteins appears to be mediated by anorexigenic gut peptides, principally cholecystokinin, glucagon-like peptide-1 and peptide YY. In the CNS, HP diets trigger the activation of noradrenergic and adrenergic neurons in the nucleus of the solitary tract and melanocortin neurons in the arcuate nucleus. Additionally, there is evidence that circulating leucine levels may modulate food intake. Leucine is associated with neural mechanisms involving mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK), energy sensors active in the control of energy intake, at least in the arcuate nucleus of the hypothalamus. In addition, HP diets inhibit the activation of opioid and GABAergic neurons in the nucleus accumbens, and thus inhibit food intake by reducing the hedonic response to food, presumably because of their low palatability. Future studies should concentrate on studying the adaptation of different neural circuits following the ingestion of protein diets.

DietaryL-Cysteine Improves the Antioxidative Potential and Lipid Metabolism in Rats Fed a Normal Diet

“…40) In particular, the majority of L-cells to secrete GLP-1 are classically believed to be located in the distal ileum and colon, although small numbers of L-cells are found throughout the small bowel. 41) Indeed, GLP-1 is known to play an important role in appetite control as well as glucose homeostasis.…”

High-protein diet selectively reduces fat mass and improves glucose tolerance in Western-type diet-induced obese rats

“…increased responsiveness to the food intake-reducing effect of the high-protein diet. Convergent functional and anatomical evidence in rats established that the high-protein diet effect is due to an increased satiety signaling rather than a low palatability of the diet or the induction of the conditioned taste aversion (20). Although an earlier study points to an initial orosensory preabsorptive poor palatability (37), subsequent results obtained using two choices and flavor testing, behavioral satiety sequence, taste reactivity in response to different percentages or sources of proteins support that the determinant of reduced daily energy intake in rats eating a high-protein diet is a protein-specific food intake-suppressive mechanism (4,5,19,30,31).…”

“…Future studies will be needed to elucidate the full extent to which alterations in circulating gut hormones and signaling pathways within the arcuate nucleus contribute to the suppression of feeding in diet-induced obese rats fed a highprotein diet. Still, many questions remain unanswered regarding the peripheral and central mechanisms of a high-protein diet underlying its beneficial effect to improve body composition with loss of fat and retention of lean body mass in diet-induced obese rats (20). Taken together, these results support an important role for high-protein diet as an additional column in the multimodal treatment of obesity in addition to dietary coaching (regular eating schedule, slow eating, reduction of fat, and carbohydrate intake), exercise, psychotherapy, drug treatment, and bariatric surgery.…”

“…There is some evidence that protein decreases appetite by increasing anorexigenic signaling (16,34,55) and stimulates thermogenesis (13,57,58) in experimental animals and humans without inducing conditioned food aversion (5). The blunting of the reduction in resting energy expenditure associated with a decrease in body weight (20,59) is another possible mechanism through which protein may facilitate long-term weight loss. It was shown that during energy restriction in human overweight and obese subjects with BMI 27-34 kg/m 2 , the 24-h energy expenditure was reduced following two low-protein diets (15% energy as protein, one high in carbohydrate, and the other one high in fat), an effect that was reduced by a high-protein diet (36% energy as protein) (59).…”

The impact of liquid preloads varying in macronutrient content on postprandial kinetics of amino acids relative to appetite

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Protein has been suggested as the most satiating macronutrient and its ingestion leads to a cascade of pre-and post-absorptive signals which regulate appetite through various pathways (1,2) . However, the exact underlying mechanisms, especially in presence of variable macronutrient composition, are not fully elucidated.

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