What do you know about umami? MSG: good or bad?

A while ago the Evidence Analysis Library (EAL) of the Academy of Nutrition and Dietetics, published the systematic review Umami and Healthy Eating and Umami in Foods. I found it very interesting and wanted to share here the most important things about umami and to discuss the safety of monosodium glutamate since there is a lot of controversy in the media.
 
What is umami?
It is called the fifth flavor and is not very easy to describe it. It´s related to a savory meaty  taste. Appreciated for centuries by oriental cultures, the term comes from Japanese, umai = delicious. There are a number of compounds that activates umami taste receptors: glutamic acid, glutamate, glutamate salts (including monosodium glutamate, potassium glutamate, calcium glutamate) and ribonucleotides such as inosinate and guanylate.
 
¿Which foods contains umami?
Glutamate is found naturally in food in either a free form as a non-essential amino acid, glutamic acid, or bound to proteins as glutamate. But, protein hydrolysis to glutamic acid is necesary for the umami taste to be sensed. Certain processes such as dehydration, fermentation, aging of food and cooking by wet methods with broths increases the release of glutamic acid and consequently the response to umami taste. Also, the more mature the fruit and vegetables, the greater the content of glutamic acid. Did you know that human milk is our first encounter with the umami flavor? Mushrooms, tomatoes, broccoli, cheeses, seafood, green tea are all good sources. 

The so-called Chinese salt or ajinomoto is basically monosodic glutamate that is widely used in Asian cuisine and in world gastronomy (not much in Argentina). It is used in small amounts as a condiment (0.3 -0.8%) since it can worsen the flavor of the preparation if used in excess.
 
What´s umami relationship with monosodium glutamate (MSG)? Does MSG have health risks?
The sodium salt of glutamate, monosodium glutamate (MSG) is used in the industry as a flavor enhancer (INS 621). It´s extracted from the sugar cane or beet molasas or from the fermentation of hydrolyzed starches from corn,cassava or rice. MSG is classified as GRAS (generally recognized as safe) by the FDA, approved by JECFA of FAO / WHO and by the Argentine Food Code.
There is a lot of controversy and myths about their safety. It is speculated that MSG could contribute to obesity, cancer, asthma, urticaria, headaches, etc. According to the review of the EAL, there were no adverse reactions to the consumption of MSG (1). It must be taken into account that: 1) the human body does not distinguish between natural glutamate in food from the additive, 2) that it´s completely metabolized by the enterocyte and practically the glutamate ingested does not pass into the bloodstream, 3) it does not cross the placenta or the brain-blood barrier, and 4) randomized double-blind studies in "sensitive" persons to MSG did not find consistent negative effects when consumed in usual quantities (2). In Europe, EFSA has established an aceptable daily intake (ADI) level of MSG of 30mg/kg/day. The usual intake of MSG in the world is estimated at 240-300 mg and twice as many in Asian countries.
 
What are the benefits of umami?
Some scientists postulate the use of glutamate as an alternative to decrease the sodium content of foods (3). Also, some claim that it could increase the power of satiety and reduce energy intake, but evidence is not conclusive on this (4). Finally, it may increase salivation in older people collaborating with the process of chewing and swallowing.
 
After all, I think we're going to see both extreme positions in favor and and against. As everything in the science of nutrition, we must carefully analyze the available evidence.  It seems to me that MSG is safe in usual quantities and that it would not be necessary to avoid foods that contain it as an additive.  As food and nutrition experts we should consider the general nutritional quality of a food product and the total diet of an individual. What do you all think?
 
-Romina