what to use when
When I first started making keto desserts, I didn't know much about the different sweeteners and so I used what worked best for the taste and structure of the desserts, that meant maltitol and isomalt. Since then I've learned a lot about which sweeteners work best for different applications, and which ones react best in our bodies.
Everyone's body is different, some people have no trouble with sugar-alcohols, other get digestive issues after consuming only a little bit. I find that the best course is to start out eating small amounts, and gradually increase over a few weeks.
Sugar-alcohols (polyols) are a type of digestive fiber, and different types have different levels of digestibility, which means that our gut microflora respond differently to different kinds, AND most importantly, they need time to adjust to the new fiber. Just like introducing beans or prunes into your diet, at first your body will react very differently than after it has acclimated.
My favorite sweeteners:
stevia - 0g carbs
erythritol - 5g carbs / 100g
xylitol - 75g carbs / 100g
isomalt - 52g carbs / 100g
My next try was isomalt and sorbitol, both of which are commonly used in commercial sugar-free products, and for good reason, they act a lot like sugar! But after a lot of comments on my videos I found out that what most keto dessert-lovers really want is full-sized desserts, not the small portions that you must stick to if you use isomalt/sorbitol (which are higher carb). I think some people are also still scared of isomalt/sorbitol just because of their association with maltitol, that can't be helped.
Most recent choice: xylitol! This one is well known in the keto and low-sugar community, as it is the easiest of the sugar-alcohols to find in nature (even if it's not produced that way commercially), and because of the small amount of research that suggests it may be good for oral health. I've settled on this as my high-heat + low-water dessert sweetener of choice, and an added benefit is that it is cheaper than maltitol, isomalt, and sorbitol (also easier to find in stores).
The best for last: now that the controversial sweeteners are out of the way, let's move on to the trusted ones: erythritol + stevia. Erythritol is great for its almost-zero carb levels, and the way it mimics sugar in high-moisture baking, BUT as we have all experienced, when you try to use it in cookies or caramel, it crystalized and turns granular as soon as it cools. :( One version of erythritol that seems magically different is Swerve brand powdered sweetener, which has ooligosacharides added, as well as "natural flavors". This one still won't stay dissolved like xylitol, but it doesn't seem to turn extremely granular and crunchy like pure erythritol does. I'm still not sure how this works. Why don't I recommend Swerve in place of normal erythritol? It's extremely expensive in comparison. :/
Lastly, we have the most "natural" of all the options, stevia. I love using liquid stevia in drinks and as a "booster" in high-water-content desserts that have already been mostly sweetened with another sweetener. This also helps with flavor, because straight stevia has a slightly bitter aftertaste, so mixing it with another sweetener helps neutralize that. Why not bake everything with stevia? It provides zero structure for baked goods, it is just a flavoring, like vanilla extract.
Final thoughts: in low-carb baking we're trying to mimic sugar, a superpower ingredients that provides moisture retention, structure, caramelization, smooth mouthfeel, tenderizing, as well as an addicting taste. We can't expect to find any one "healthy" ingredient to do everything that sugar does, so the best bet is to mix ingredients. For the best-tasting low-carb desserts, I recommend a mix of 40% xylitol, 60% swerve for medium-moisture desserts (cakes, ice creams, cheesecakes, brownies, etc), 50% swerve + few drops of stevia for high-moisture desserts (puddings, custards, drinks, etc.), and pure xylitol for low-moisture desserts (caramel, candies, cookies). Why don't all my recipes follow this formula? The carb-count is too high when using xylitol, most Americans (50% of my audience) are used to eating large portion sizes, and so I've gotten many complaints that xylitol makes my recipes too high-carb for keto, supposedly "no one is willing to eat such small portions of dessert". At the end of the day, you can use erythritol or stevia in all desserts recipes, but you won't get a very good texture, structure, or moisture level, in other words, it won't taste very good!
Being on a keto diet requires making some sacrifices. If you want amazing tasting desserts that are very close to the full-carb versions, you will almost always have to be content with smaller portion sizes. The reason I started this channel is because of the reactions I would get from people who were diabetic or had just started keto, and had just tasted my desserts for the first time. The look on their faces when I told them they could have more than just a nibble and it wouldn't affect their blood sugar, that reaction of amazement made me so happy. Now that keto is growing in popularity, it's more common that I deal with seasoned keto-dieters who have lost appreciation for the fact that, even on a sugar-free, low-carb diet, we can somehow still have dessert.