Marshmallows are high in sugar; very unhealthy food and it is not advisable for you to give any to your dog.
Marshmallows probably aren’t going to be on anyone’s list of healthy or natural foods. They are a spongy candy made from sugar, corn syrup, gelatin, vanilla extract, and coated with cornstarch or confectioner’s sugar.
There is nothing in marshmallows that is harmful or toxic to dogs, but they contain lots of sugar.
Small amounts of marshmallow will not harm your dog, but because they are high in sugar, if a dog eats a large amount it can get sick.
If your dog eats too many marshmallows it can begin to vomit and it can get diarrhea. Depending on the size of your dog, if it ate a lot of marshmallows, and have severe vomiting or diarrhea, you should bring it to a vet.