Jay Mann delivered this address with accompanying liquid refreshment (with and without MSG) at last year’s conference.
A large number of food manufacturers seem to be selling their food on the basis of what it does not contain, rather than on the basis of the actual ingredients. These negative statements, such as “no added MSG” and “no preservatives” are clearly intended to imply some sort of benefit from the omission of such ingredients.
Aside from the question of whether food should be marketed on negative issues, there is considerable evidence that no health benefit whatsoever accrues by omission of MSG and preservatives.
Since the “no preservative” claim is well-nigh universal on supermarket shelves, I suggest that there is a potential niche market amongst scientifically literate consumers who dislike food wastage.
I mainly want to consider, however, the MSG issue. The first question is why anyone would want to add MSG to food. The next is why the public is concerned about added MSG.
Some historical background. For centuries, traditional Japanese cooking has used “dashi” as the basic sauce ingredient. Dashi is an extract of certain seaweed (“sea tangles”) and of dried bonito. Although, to my palate, the flavour of dashi is not particularly attractive, it greatly enhances the flavour of other foods. In 1908, a Japanese scientist showed that glutamic acid, coming from the seaweed, is the main flavour-enhancing chemical in dashi. Monosodium glutamate, a chemically convenient form of glutamic acid, almost immediately became an important flavour enhancer made through fermentation.
Another chemical called inosine monophosphate (IMP), originating in the bonito muscle, was also discovered in dashi. IMP and related compounds such as guanylic acid (GMP) are characteristic nucleotides found in muscle tissue from both mammals and fish. These nucleotides too are used as flavour enhancers although they are considerably more expensive than MSG (Table 1).
A brief chemistry lesson. Glutamic acid, a naturally occurring amino acid, is a major part of almost every protein. Glutamic acid bound within protein has no particular taste, but free glutamic acid can be released by, for instance, ageing of meat, or by cooking. Thus the presence of glutamic acid in a food is a biochemical hint that the food may contain protein.
In neutral or alkaline solutions, glutamic acid becomes a salt and can now be called “glutamate”. Monosodium glutamate (MSG) is a white crystalline powder. In the presence of water, MSG separates into glutamate ions and sodium ions (which may add some salty taste). Foods as eaten have only glutamate, not MSG. The glutamate may come either from added MSG or from other sources.
The vital point is that although “MSG” might be added to a food, what is found in the food is “glutamate”. Even scientific authors have confused the issue. For instance, Rhodes et al. (1991) analysed foods for glutamate yet reported their results in terms of “MSG”, without even having confirmed whether enough sodium ions were present.
Why Add it?
Why add glutamate to food? The answer is simple: it makes most foods (except sweets) taste better (Yamaguchi 1991). You can confirm this yourself by adding about 0.1% MSG to a sample of soup or stew. Even at low concentrations where its “meaty” taste cannot be detected, glutamate can enhance the flavour of other ingredients.
Words such as “more pleasant”, “more savoury” and “more satisfying” have been used (Rogers and Blundell 1990). Both Japanese and Australians have similar responses (Prescott et al 1992). Glutamate concentrations of about 0.1 to 0.3% are recommended by MSG manufacturers (Table 2). Older folk have duller tastebuds, requiring about three times higher levels of added MSG than younger people (Schiffman et al 1994). Perhaps that is why older people have such poor appetites; MSG in rest-home cafeterias may improve the nutrition of the elderly (Bellisle et al 1991).
Is there some biological reason why we should prefer food with higher levels of this particular amino acid? Since finding food with adequate levels of protein has generally been a problem with our animal ancestors, any mechanism whereby an animal can pick out foods with higher levels of protein might be advantageous. Glutamate can be liberated when the protein is partly hydrolysed by ageing, fermenting, boiling, or possibly even during chewing.
If glutamate is so common, why do we have to add MSG to our foods? In fact, sometimes we don’t. A number of common food ingredients such as tomatoes, mushrooms, and parmesan cheese (Table 3) have high levels of free glutamate.
Is it only a coincidence that these are common cooking ingredients? Unlikely. The US. Food and Drug Administration reported in 1995 that Italian food contains higher levels of free glutamate than any other ethnic food. If glutamate were the real cause of Chinese restaurant syndrome, it would be called “Italian restaurant syndrome”.
The absence of “Italian restaurant syndrome” confirms the laboratory findings clearing MSG of blame. (Alternatively, we shall now see an American epidemic of damage claims against Italian restaurants.)
Food manufacturers are well aware of the taste-enhancing properties of added glutamate. Although pandering to the general public’s fear of “chemicals” by slapping a “no added MSG” claim on the label, they add ingredients like soy sauce, fish sauce, yeast or meat extract, and especially hydrolysed vegetable protein, in order to increase their product’s glutamate level. The hydrolysed vegetable proteins typically provide 10-30% of their dry weight as glutamate.
Why Not Add MSG?
There is no doubt that a large proportion of the general public is afraid of MSG. How did this arise? (The interested reader should look up the detailed reviews published by Taliaferro 1985 as well as Pulce et al 1992.)
In 1968, a Chinese-American, Dr Robert Kwok, wrote a letter to the New England Journal of Medicine, in which he described some mild but uncomfortable symptoms experienced after dining at certain Chinese restaurants. This was the origin of the catchy phrase “Chinese restaurant syndrome”, often abbreviated as CRS. Because Dr Kwok got symptoms only from some but not all restaurants, he suspected that the cause might be an ingredient not used by all chefs. Among his list of possibilities was MSG, together with soy sauce, cooking wine, and high sodium.
A year later, well-publicised experiments from a St Louis laboratory claimed that injections of about 2g MSG per kg bodyweight resulted in temporary behavioural changes and brain lesions of newborn rhesus monkeys. Although there has been considerable discussion as to the physiological significance of such high doses (equivalent to 150g MSG for an adult man), the issue is moot since no one has been able to reproduce the original experimental work.
It has been suggested that either Dr Olney’s monkeys were kept under very poor conditions, or that the methods for preparing the brain tissue for microscopic examination were themselves responsible for causing tears that were misinterpreted as brain lesions (Taliaferro, 1995). (Mice, which are the most sensitive mammals to glutamate, show behavioural changes — but not brain lesions — when force-fed the equivalent of 120g glutamate for a 30-kg child. Three-generation studies of mice fed lower levels every day showed no effects of glutamate.)
These two reports started a new MSG-bashing career path for many scientists. Rather than go into details of the dozens of studies reported, I will summarise their conclusions:
1) Certain severe asthmatics can experience asthma attacks about 6 hours after ingesting gram quantities of MSG (Allen et al, 1987). Moneret-Vautrin (1987) concluded that “a very small subset of patients with intrinsic asthma might present with an intolerance to MSG if high doses are consumed”. About half of such asthmatics are also sensitive to salicylates (in aspirin as well as foods like tomatoes). What percentage of the population is affected by MSG-induced asthma is not known, and no one has suggested that MSG is important in most asthmatics.
2) Some people may develop headaches after eating MSG on an empty stomach (Scopp 1991). This is not a normal way to eat MSG. When MSG is consumed with other foods, it has no effect on blood glutamate levels (Stegink et al 1983). It is not clear whether headaches can be caused by eating MSG mixed with food, nor is the percentage of the population so affected known.
3) MSG does not cause the symptoms of Chinese restaurant syndrome (Kenney 1986). To the extent that we can be sure of anything in an uncertain universe, this is a fact! Although 20-40% of the population believe they have a food intolerance, the correct figure is probably about 5% (Young et al 1994; Somewhere between 0.2% and 1% of the population suffer from CRS-like symptoms, generally not linked with Chinese food (Kerr et al 1979). No MSG-induced flushing could be found in volunteers, including 18 people subject to CRS (Wilkin 1986). When the flavour of MSG is concealed there was no significant difference between the number of reactions reported to MSG versus placebo capsules. The strong role of suggestion is shown by the fact that about 15% of both groups reported “symptoms” (Tarasoff and Kelly 1993). In 1995, the FDA sponsored an extensive review carried out by the Federation of Societies for Experimental Biology (FASEB). This review concluded that there was no evidence for a link between CRS and MSG.
The “classical” symptoms of CRS are as shown in part 1 of Table 4. Many people who occasionally get uncomfortable sensations after eating Chinese food may be sensitive to histamine (Part 2, Table 4). Histamine, produced from another natural amino acid histidine, is not ordinarily absorbed from the gut. Temporary minor damage to the gut lining may let histamine enter the circulation.
Some possible sources of histamine are fermented sauces such as soya sauce and fish sauce. Soya sauces made by chemical hydrolysis would have little histamine, in contrast to more expensive soya sauces made through fermentation. Thus one Chinese restaurant might use ingredients with free histamine while another might not.
Histamine effects are so common that they have been called “scombroid poisoning” when they occur in in people who have eaten inadequately refrigerated red-meat fish such as tuna, albacore, herring, and mackerel. Bacteria in the fish muscles can form significant amounts of histamine during storage without the fish being spoiled or off-taste. For someone suffering from histamine-induced symptoms, the obvious remedy is to take an antihistamine.
Allergies to food ingredients are also common (Part 3, Table 4). Some of the most common foods causing allergic reactions are shrimp, peanuts, and members of the parsley family (such as coriander) (de Maat-Bleeker, 1992; Settipane 1987). Since some Chinese recipes call for addition of dried shrimp to vegetable dishes, a dish’s name may not define the kinds of potential allergens in it. Once again, antihistamines are the recommended treatment.
What’s Wrong with the “No added MSG” label?
1) The rare victims of CRS are being actively misled by the “no added MSG” labels on foods. Avoiding foods with MSG in no way improves their chances of avoiding symptoms. (Ignorance is not bliss.) Foods with “no added MSG” often contain hydrolysed fish or bean sauces, which are more likely to contain CRS-inducing chemicals.
2) People with glutamate-caused asthma may be deceived by a “no added MSG” label into eating foods with high levels of glutamate, either from natural ingredients such as tomatoes and cheese, or from addition of hydrolysed vegetable protein.
3) Some people who are sensitive to proteins from wheat or from soy may unknowingly ingest them from “hydrolysed vegetable protein”.
4) The “no MSG” label claim is deceptive in all but the most narrow legal interpretation, where glutamate has been added intentionally through other means. If a manufacturer is so willing to use “sharp practice” in this aspect of his labelling, why should I trust his honesty in regard to other claims, such as taste and quality? (I have nothing against a manufacturer who does not use MSG, as evidenced on the ingredient listing of his product, without pandering to popular prejudice with a “no added this – no added that” claim.)
(References available from the editor.)
Table 1: “E-Numbers” of approved Flavour Enhancers
- E620 Glutamic acid
- E621 Monosodium glutamate
- E622 Monopotassium glutamate
- E623 Calcium diglutamate
- E624 Monoammonium glutamate
- E625 Magnesium diglutamate
- E626 Guanylic acid
- E627 Disodium guanylate
- E628 Dipotassium guanylate
- E629 Calcium guanylate
- E630 Inosinic acid
- E631 Disodium inosinate
- E632 Dipotassium inosinate
- E633 Calcium inosinate
- E634 Calcium 5′-ribonucleotides
- E635 Disodium 5′-ribonucleotides
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Table 2. Recommended Usage Rates for MSG and IMP (mg/100g)
|Canned poultry, sausages, ham||100-200||6-10|
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Table 3. Natural Glutamate Content of Foods (mg per 100 g)
|Ingredient||Total glutamate||Free glutamate|
|Meat & yeast extracts||450-18||930|
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