There are many different ways to thicken your low carb sauce without using the traditional starches. Here are some alternatives.

Vegetable gums

Vegetable gums are used a lot in Asian cooking, but can be used in all kinds of sauces you need to thicken. Xanthan gum and guar gum are the most commonly used. Vegetable gums are a type of fiber that absorbs water and forms into a gel. Personally I often use locust bean gum and I shake it into water before adding it to the dish I need to thicken. Others recommend to sprinkle vegetable gums into your sauce while whisking. You will only need a small amount, so watch the amount to avoid that it becomes too jel-like.

There are also products available that contain a mix of different vegetable gums and are easier to use. One of them is ThickenThin Not/Starch. I have not yet tried this product myself, but I have seen it recommended by others. Some comments I have seen by people that have used both ThickenThin Not/Starch and pure vegetables gum, is that the consistency of the sauses get better with ThickenThin.

Reduction

This is a simple and important method to master when cooking sauces, also those including starch as a thickener. Reduction is performed by simmering your potential sauce until enough moisture evaporates and you get the desired volume on your sauce. This will intensify the flavors. You can also add fats toward the end of the process to get a richer sauce.

Full fat dairy products

Fats can be good thickeners. Butter, sour cream and heavy cream can all work as thickeners in your sauce. If you avoid dairy products you could try using full fat coconut milk.

Egg yolks

Allemande sauce from french cuisine is a typical example of a sauce where egg yolks are used to thicken it. Other popular sauces that are traditionally thickened using egg yolks are hollandaise and béarnaise. Egg yolks are especially suited when there are fat in your sauce.

Pureed vegetables

This works best for vegetable soups, such as my low carb cauliflower soup, but it could be used for sauces as well.

Nuts

Ground nuts, such as almond meal and other nut flours can also be used to thicken your sauce, but the taste of the nuts might not suit your sauce

Other alternatives

Some uses coconut flour, but it seems from comments that few people think it is a success in a sauce. I have also seen some use flax seeds, I haven’t tried it, but it seems to give a texture most people don’t like.