You might not have heard of hydrolyzed vegetable protein, but you’ve surely heard of its villainous cousin, monosodium glutamate — or MSG — the culprit behind the so-called “Chinese restaurant syndrome.” The Japanese have been using MSG, derived from seaweed, for thousands of years, and it is the third most prevalent flavour enhancer in the world after salt and pepper.

MSG has been in the media for decades because of its associated side effects, including feelings of numbness, tingling, headaches, and heart palpitations. Though it is debatable, some believe it is neurotoxic — in other words, it may be poisonous to nerves and neurons.

In addition to these common criticisms, a 2008 study published in the journal Obesity illustrated that MSG may also be a contributor to obesity, due to its effects on leptin resistance. Leptin is a hormone that regulates appetite and metabolism. It acts primarily as an appetite suppressant, and therefore any substance that inhibits leptin will increase food intake, creating a risk for obesity. Whether or not MSG is responsible for these side effects, the public’s concern has prompted many restaurants to advertise “no MSG.” However, this claim does not necessarily mean that you are not consuming one of MSG’s many close relatives — such as hydrolyzed plant protein, hydrolyzed soy protein, autolyzed yeast extract, or the previously mentioned hydrolyzed vegetable protein — on a daily basis since these ingredients are virtually inescapable in today’s food system, and produce the same potentially harmful effects associated with MSG.

The common factor among this family of ingredients is the presence of an amino acid called glutamic acid, or glutamate, depending on its form. Glutamate is a flavour enhancer because of the carboxylic acid group it possesses, which stimulates a specific taste receptor on the tongue. This receptor is responsible for detecting the umami taste, which was discovered in Japan in 1908, and is considered the fifth taste, alongside salty, sweet, sour, and bitter.

Glutamate imparts flavour to many foods. It is present in the protein component of parmesan cheese, eggs, salmon, chicken, beef, and pork, and is responsible for their savoury taste. However, when glutamate is found in MSG or hydrolyzed vegetable protein, it is in its free form, thus enabling its potential negative side effects.

MSG and its relatives are everywhere. They’re most commonly found in flavoured potato chips, frozen dinners, canned soups, and canned meats. Many restaurant chains deceptively use ingredients like hydrolyzed plant protein, which is found in Big Mac sauce and many of its chicken products. For decades, MSG was an important ingredient in baby food, but fortunately this is no longer the case.