Carbohydrate craving, obesity and brain serotonin

Appetite. 1986;7 Suppl:99-103. doi: 10.1016/s0195-6663(86)80055-1.

Abstract

One mechanism through which the brain obtains information about the composition of the diet involves food-induced changes in the plasma amino acid pattern (principally the "plasma tryptophan ratio"), which then cause increases or decreases in brain tryptophan levels, and in the synthesis of a neurotransmitter, serotonin, which is formed from the tryptophan. A carbohydrate-rich, protein-poor meal stimulates insulin secretion; this diminishes plasma levels of the amino acids which compete with tryptophan for transport into the brain (e.g., leucine, isoleucine and valine), thus increasing tryptophan's flux across the blood-brain barrier and its brain levels. In contrast, a high-protein meal contributes so much more of these latter amino acids to the blood stream than of the relatively-scarce tryptophan that it diminishes tryptophan's entry into the brain. This article reviews evidence that the brain actually utilizes the food-induced changes in brain serotonin in order to make choices about what to eat at the next meal. It also discusses the likelihood that a disturbance in this mechanism is involved in producing the "carbohydrate-craving" that is frequently associated with obesity. (This behavior which has been studied by allowing hospitalized subjects to choose freely among isocaloric meals and snacks of varying protein/carbohydrate ratios, typically manifests itself as a propensity to consume 30 per cent or more of the total daily calorie intake in the form of sweet or starchy snacks, usually at a characteristic time of day.) D-Fenfluramine, a drug that selectively enhances serotonin-mediated neurotransmission, also selectively suppresses "carbohydrate-craving" in these subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

MeSH terms

  • Amino Acids / blood
  • Brain Chemistry*
  • Dietary Carbohydrates / pharmacology
  • Dietary Fats / pharmacology
  • Dietary Proteins / pharmacology
  • Feeding Behavior / physiology*
  • Humans
  • Hunger / physiology*
  • Insulin / metabolism
  • Insulin Secretion
  • Obesity / etiology*
  • Obesity / physiopathology
  • Serotonin / analysis*

Substances

  • Amino Acids
  • Dietary Carbohydrates
  • Dietary Fats
  • Dietary Proteins
  • Insulin
  • Serotonin