The
sodium salt of
glutamate (
monosodium glutamate;
MSG) imparts a savory/meaty taste to foods, and has been used as a
flavoring agent for millennia. Past research on
MSG/
glutamate has evaluated its physiologic, metabolic and behavioral actions, and its safety. Ingested
MSG has been found to be safe, and to produce no remarkable effects, except on taste. However, some recent epidemiologic and animal studies have associated
MSG use with
obesity and aberrations in fat metabolism. Reported effects are usually attributed to direct actions of ingested
MSG in brain. As these observations conflict with past
MSG research findings, a symposium was convened at the 13th International Congress on
Amino Acids, Peptides and Proteins to discuss them. The principal conclusions were: (1) the proposed link between
MSG intake and
weight gain is likely explained by co-varying environmental factors (e.g., diet, physical activity) linked to the "nutrition transition" in developing Asian countries. (2) Controlled intervention studies adding
MSG to the diet of animals and humans show no effect on
body weight. (3) Hypotheses positing dietary
MSG effects on
body weight involve results from rodent
MSG injection studies that link
MSG to actions in brain not applicable to
MSG ingestion studies. The fundamental reason is that
glutamate is metabolically compartmentalized in the body, and generally does not passively cross
biologic membranes. Hence, almost no ingested
glutamate/
MSG passes from gut into blood, and essentially none transits placenta from maternal to fetal circulation, or crosses the blood-brain barrier. Dietary
MSG, therefore, does not gain access to brain. Overall, it appears that normal dietary
MSG use is unlikely to influence energy intake,
body weight or fat metabolism.