In fact, there's a group of people that are known as "junk food vegans" because they only eat non-natural vegan products, which aren't always healthy.
For example, french fries are vegan, but I wouldn't be able to eat that all day. Vegan food can also be greasy, high in sugars, and salt.
It isn't enough to eliminate meat, eggs, and dairy. You have to still maintain a balanced diet of fruit, vegetables, legumes, grains, and protein.