I think vice taxes are a great tool to discourage behavior that affects public health but we need to increase them.
However it’s a lot harder to create a vice tax on food. It would be great to make poor food choices more expensive than better choices but I don’t see how you can draw clear lines, nor be effective. For example this obese person doesn’t eat much junk or overly processed food so even if you could clearly define junk food, a vice tax wouldn’t help