The taste of umami
Umami — Japanese for ‘deliciousness’ — is what we in the West might think of as savoury. The flavour is central to much Asian cooking, and the molecule responsible was first identified in the Japanese stock dashi. Recently, taste receptors for this molecule were shown to exist on our tongues, and umami is now considered to be one of the basic tastes, along with sweet, sour, salty and bitter. What is the molecule? It is glutamate.
Glutamate is an amino acid (glutamic acid). It is a building block for proteins (along with the other 19 amino acids). It is the most abundant amino acid in the body (and in nature), and is found mostly in gut, muscle and the brain. In muscle it plays a central role in energy pathways (and is taken as an exercise supplement by some). In the brain, it is the principle excitatory neurotransmitter (communicating molecule between neurons). Without it the brain would stop. It is the principle energy source for cells in the gut wall that extract nutrients and protect us from pathogens. Glutamate is thus an essential part of our chemistry and our life.
We eat glutamate all the time (because the body wants it), and the taste-receptors that register umami as pleasant reward us for doing so. It is omnipresent in natural and prepared foods — a partial list includes mushrooms, miso, soy sauce, parmesan cheese, dried hams and aged beef (enzymes break down meat protein to free glutamate), dashi, tomatoes, vegemite, marmite and fish sauce. Its highest concentration is in seaweeds (the giant kelp that is a principal component of dashi). We maximize dietary glutamate by eating these foods in combination (e.g. pasta with tomato and mushroom sauce topped with parmesan cheese — it’s not confined to Asian cuisine). Human breast milk has 10 times the concentration of glutamate as cow’s milk. We are nurtured on glutamate.
So, how did a glutamate salt get so demonized?
MSG (monosodium glutamate, or simply sodium glutamate; I’m not aware there is a disodium glutamate), is just what its name suggests, a single sodium ion attached to glutamate. As soon as MSG hits water, it dissolves and the sodium ion separates from the glutamate. MSG is now glutamate as far as the body is concerned — there is no difference between the glutamate in MSG and the glutamate in vegemite. The same thing happens to table salt (monosodium chloride), which separates into sodium ions and chloride ions when dissolved in water. The amount of sodium in MSG is about a third of that for table salt (weight-for-weight).
MSG was originally extracted from the wheat protein gluten (which gave glutamate its name). Presently, it is obtained from fermentation, a similar process that leads to the high glutamate levels in yeast extracts such as vegemite. It’s been done since antiquity — the Romans created a fermented fish sauce (garum) that was also high in MSG.
The bad press for MSG started in 1968. Dr Robert Ho Man Kwok (MD) sent a letter to the New England Journal of Medicine in which he described symptoms he was experiencing some hours after eating at Chinese restaurants in America. Remarkably, the letter was published, and given the heading ‘Chinese restaurant syndrome”. I can’t help but wonder if it was published as a little light relief in a heavyweight journal, but it went viral (so to speak), and a new Western disorder was born (you don’t hear of the Chinese getting Chinese restaurant syndrome). Kwok suggested multiple possibilities in his letter, including cooking with wine and saltiness, but only MSG was pounced on. I’m guessing it had a chemical-sounding name.
Since this anecdotal report by a single individual, multiple studies have been undertaken into the health consequences of MSG. The overwhelming evidence is that consuming MSG in even high doses with food (especially carbohydrates) is safe. Placebo-controlled trials show no difference in symptomatology between placebo and MSG, even in people who identify with Chinese restaurant syndrome.
Glutamate can be intercepted by cells in the gut mucosa and used as their energy source. The gut signals to the brain (via the vagus nerve) when enough is enough, and this leads to avoidance of further intake (and the upper limit to appetite for umami). Glutamate in the blood doesn’t cross into the brain (the blood-brain barrier doesn’t allow glutamate to enter the brain, the brain makes its own glutamate, and excess is transported the other way into the blood stream where it is carried away). Disturbance to these balances would threaten essential human chemistry.
It all started with an anecdote, and now it’s up to anecdote to keep the role of MSG in Chinese restaurant syndrome alive. Anecdote can be very powerful though — hard science is readily dismissed (ask a climatologist). This comes from an anti-MSG site: “conventional medicine lacks in understanding what many patients have already found”. I think that sums up the dichotomy.
The vilification of MSG remains unique among food ingredients and, as a result, it is one of the most extensively studied ingredients in our food supply. The science is clear, both experimentally and from our understanding of human biology — dietary glutamate is safe for human consumption. No mechanism has been convincingly proposed whereby it could be otherwise.
If Chinese restaurant syndrome is real, then it is not due to MSG.