The problem with xanthan gum is that anything with the name “gum” is inevitably considered synthetic.
Nobody wants a synthetic, a plastic, it can’t be good.
It is not synthetic at all, it is the product of the bacterium Xanthamonas campestris when it eats simple sugars, and the result is a very hygroscopic carbohydrate, i.e. it absorbs a lot of water.
So the question is: who gave it the name “chewing gum”?
Probably someone who has not studied marketing.
What is it used for?
In cooking, it is used for obvious reasons: to thicken, give texture, consistency, and this without adding flavor, which makes it a very valuable tool.
It is, for example, a good complement to erythritol, as it will prevent the (re)formation of erythritol crystals and thus reduce its cold effect (you have a post on how to cook with erythritol here).
However, it also has other non-edible uses.
For example, it is used as a thickener in paints.
If this sounds bad to you, you will be calmer when you know that potato starch also has its uses in paint or to make plastic bags (biodegradable).
It is also important to know that we have been consuming it since 1969 (when it was approved for use in food), which means that we have known about it for many years.
It is very hygroscopic, and it is supposed to be so because of its structure that includes a glucose and some branching of adjacent saccharides (you can see the image on wikipedia and read more here).
And this gives rise to the following properties:
When a force (pressure) is applied, its viscosity decreases.
When a temperature is applied, its viscosity decreases again.
The first has little application in cooking (in the sense that you don’t shake a salad before eating it, or a mayonnaise).
But the second does, because you can expect that when a dish (I’m thinking desserts) or sauce cools, it will thicken at room temperature (i.e., don’t go adding xanthan gum to thicken a hot mixture, because when it cools, it will be like a stone).
When it finds calcium (in the form of calcium phosphate ion, not the mineral calcium carbonate found in our bones or teeth), then it forms a thick gel, i.e. in combination with milk or yogurt.
And probably the most important application in the cooking world:
When a mayonnaise breaks… xanthan gum is your friend.
Carbohydrates and the microbiota
Although xanthan gum is a carbohydrate, it is a resistant carbohydrate and therefore counts as zero in the keto diet.
The microbiota can consume it, and studies show that it is a good additive from a health point of view, such as this entry in dogs, as a protector against aggressions such as antibiotics (study, and even with antitumor activity (study…).
At high (or very high) doses, an improvement in cholesterol and sugar levels (study, study and a certain laxative effect (logical, being all fiber, although in this sense the hygroscopic character only softens the stool).
So perfectly safe and even recommended, but with one exception.
Not for newborns
The presence of xanthan gum as a thickener in milk (formula or breast) is suspected to have favored bacterial growth in newborns, causing necrotizing enterocolitis (wikipedia, and since then it is not recommended for use in children under 12 months).
The problem is not the type of bacteria in question, but the immaturity of the newborn’s digestive system, as the bacteria in question are not beneficial.
This is somewhat reminiscent of the question of honey, which is strongly discouraged for children under 12 months for exactly the same reason (an immature digestive system).