Depends on their motivation. If they're genuinely concerned about your health they're probably a good friend.

I mean, I tend to give all of my friends a hard time about sweets and sugary drinks, and expect the same. Most everyone I know understands that it’s best to avoid sugar, but it is both truly ubiquitous and extremely addictive so it’s essential impossible. Trying to not get into an icecream/chocolate habit is a never ending battle.