Natural ways to sweeten overnight oats might depend on your definition of natural. Good options include raw honey (the most natural), maple syrup, brown rice syrup, yacon syrup, date syrup, and monk fruit based options such as zero-sugar honey and zero sugar maple syrup made from real natural sugars. Stirring in a little low-sugar jam also sweetens overnight oats. Flavored stevia drops is another option but some people do not care for the bitter aftertaste.