Anecdotal evidence blames the consumption of MSG for several symptoms such as headache, nausea, weakness, heart palpitations etc. Most migraine literature cites MSG as a potential trigger (example) but usually without any scientific basis. A quick google search gives plenty more reasons that it might be bad for your health.
Are there any reliable studies that support MSG being associated with any kind of health problem, major or minor?
DISCLAIMER: I've just ripped this, almost verbatim, from my answer to the Is Soy bad for you? question.
Some people are exquisitely sensitive to glutamates (e.g. MSG).
From wikipedia:
Australia and New Zealand
Food Standards Australia New Zealand (FSANZ) cites "overwhelming evidence from a large number of scientific studies" to explicitly deny any link between MSG and "serious adverse reactions" or "long-lasting effects", declaring MSG "safe for the general population". It does, however, describe that in less than 1% of the population, sensitive individuals may experience "transient" side effects such as "headache, numbness/tingling, flushing, muscle tightness, and generalised weakness" to a large amount of MSG taken in a single meal.
[Emphasis mine.]
United States
Monosodium glutamate is one of several forms of glutamic acid found in foods, in large part because glutamic acid, being an amino acid, is pervasive in nature. Glutamic acid and its salts can also be present in a wide variety of other additives...
The toxicity of MSG is an area of some debate. The noted scientist John Olney (of Olney's lesions fame) was an outspoken critic of the addition of MSG to foods.
There is some evidence that MSG may be linked to obesity.
Association of Monosodium Glutamate Intake With Overweight in Chinese Adults: The INTERMAP Study
This study examines the association between MSG intake and overweight in humans. We conducted a cross-sectional study involving 752 healthy Chinese (48.7% women), aged 40–59 years, randomly sampled from three rural villages in north and south China. [...] With adjustment for potential confounders including physical activity and total energy intake, MSG intake was positively related to BMI. Prevalence of overweight was significantly higher in MSG users than nonusers. [...] This research provides data that MSG intake may be associated with increased risk of overweight independent of physical activity and total energy intake in humans.
On the other side of the coin, a study funded by a Japanese MSG manufacturer (Ajinomoto) found:
Monosodium l-glutamate (MSG), an umami taste substance, may be a key molecule coupled to a food intake signaling pathway, possibly mediated through a specific l-glutamate (GLU) sensing mechanism in the gastrointestinal tract. Here we investigated the effect of the spontaneous ingestion of a 1% MSG solution and water on food intake and body weight in male Sprague–Dawley rats fed diets of varying caloric density, fat and carbohydrate contents. Fat mass and lean mass in the abdomen, blood pressure, and several blood metabolic markers were also measured. Rats given free access to MSG and water showed a high preference (93–97%) for the MSG solution, regardless of the diet they consumed. Rats ingesting MSG had a significantly smaller weight gain, reduced abdominal fat mass, and lower plasma leptin levels, compared to rats ingesting water alone. Naso-anal length, lean mass, food and energy intakes, blood pressure, blood glucose, and plasma levels of insulin, triglyceride, total cholesterol, albumin, and GLU were not influenced by the ingestion of the MSG solution. These same effects were observed in a study of adult rats. Together, these results suggest that MSG ingestion reduces weight gain, body fat mass, and plasma leptin levels. Moreover, these changes are likely to be mediated by increased energy expenditure, not reduced energy intake or delayed development. Conceivably, these effects of MSG might be mediated via gut GLU receptors functionally linked to afferent branches of the vagus nerve in the gut, or the afferent sensory nerves in the oral cavity.
Summary
For some people, low doses of MSG may cause health problems1 such as obesity, headache, flushing, sweating, facial pressure or tightness, numbness, tingling or burning in face, neck and other areas, rapid, fluttering heartbeats (heart palpitations), chest pain, nausea, weakness.2
1I have retinitis pigmentosa. One of the prominent aspects of the disease is severe photopsia. MSG is the best trigger factor I have found for photopsia. I realize this is an n=1 study group size but I thought I'd put it out there.
No. Carefully blinded trials don't reproduce the effects claimed
It would be extremely surprising if MSG was dangerous to people as glutamic acid the amino acid exists in all our proteins and we will all therefore contain some glutamate (the salt of the free acid).
But it is possible that some people could be particularly sensitive to large amounts of it if added to food. The problem is that studies done with good scientific controls (double blinded) have never consistently shown that even those people who claim such sensitivity suffer the adverse effects when actually given MSG (and don't suffer them when even something other than MSG). As one review put it:
Work over the past 17 years has consistently failed to reveal any objective sign accompanying the transient sensations that some individuals experience after the experimental ingestion of monosodium glutamate and it is questionable whether the term 'Chinese Restaurant Syndrome' has any validity. When some common food materials are used in the same experimental setting, similar symptoms can be produced in a limited number of people. Double-blind testing of individuals who identify themselves as suffering the 'syndrome' has failed to confirm the role of monosodium glutamate as the provocative agent.
I think that is pretty solid evidence that it isn't bad for you.
I did look this up sometime ago, in the context of pregnancy. Almost all the health concerns are skeptical based on random and possible connections I have not found any documented scientific experiments/studies with proven results; either way. On the other hand, asian cuisine has used MSG for years.
The only thing to be careful of, is if you are allergic to MSG. There have been recorded incidents of serious reactions to MSG..
