Is the baker who makes cakes distributed for the sake of Allah sinful if diabetics or those suffering from excessive obesity eat from them?

What you are doing, baking cakes and giving them as charity, is a good deed for which you will be rewarded, Allah willing. If those receiving the charity are diabetic or obese and eat from it knowing its harm, there is no sin upon you. Rather, the sin is upon them because they are responsible for their own actions. However, if they do not know of its harm, then you must inform them.