Sweeteners are added to many protein powders to balance the often neutral to slightly bitter taste of the protein itself. A rough distinction is made between low-calorie sweeteners such as sucralose or steviol glycosides and sugar alcohols such as erythritol, which each taste differently sweet and can differ in how well they are tolerated. Some manufacturers also rely on combinations of several sweeteners to balance flavour and aftertaste better.
In the ingredient list of a protein powder, sweeteners are usually near the end, as they are only needed in small amounts. Some sugar alcohols can affect digestion in larger amounts, so it can make sense to approach new products gradually. Which sweeteners are included can be found in the ingredient list on the packaging. If you react sensitively to certain sugar alcohols, you can specifically look for products with other sweeteners.
How to read the ingredient list of a protein powder overall is explained in the guide Reading the ingredient list of protein powder, and more on ingredient lists in general is offered by the entry Ingredient list.
