Again, it depends on the brand and how often you're indulging. Traditional eggnog recipes call for heavy cream, whole milk, egg yolks, and sugar, among other ingredients, which would definitely have the potential to make you gain weight. Generally speaking, vegan eggnogs available at stores are lighter in terms of calories, fat, and, often, added sugars. You can also help to control the nutrition by considering making your own eggnog from scratch. As always, check the nutrition label before making your purchase. I suggest choosing a brand that has as few grams of added sugar and saturated fat as possible!