When you see the word lecithin on an ingredients list (say, on a bar of chocolate), it might sound like a chemical filler, but it's actually a naturally occurring substance derived from both animal and plant sources. It's used to thicken or stabilize ingredients. One of the most common types is soy lecithin. If you want to avoid soy, here are some alternatives that you can use at home.
If a recipe calls for lecithin as a thickener, you can use cocoa butter instead. Just note that it contains more fat than lecithin and is more expensive. In breads, substitute it in equal measure. If you're concerned about cocoa butter affecting the taste of your recipe, look for deodorized cocoa butter.
Egg yolk is an easy-to-find lecithin substitute and a very effective emulsifier or binder. Substitute one large egg yolk for every tablespoon of lecithin powder. Egg yolks also have a much higher fat content than lecithin. If that's a problem, look for an egg replacer powder at your local health foods store. Follow the instructions on the box for proper measurements.
Some people like to avoid soy because of its estrogenic effects, or because it's typically genetically modified unless organic or labeled non GMO. Sunflower lecithin is a better alternative in this case. It's extracted using a cold-press process without harsh chemical solvents, making it the only raw type of lecithin.