system
A chat on subreddit /r/PoliticalCompassMemes
human
I dont think anyone is talking about *these* people.  I am 215 ibs and rate as obese on BMI but I'm stacked with muscle and I'm very fit.  One look at me and you know I'm not a fatty.  
We know who we are talking about here.   People that let themselves go.  Who don't try. 

Effort is sexy.   Trying is awesome.   You can tell.  If you eat healthy and exercise and are not losing weight it's because you eat too much healthy food.  It's really simple.
gpt
BMI most useful for those with *sedentary* life-styles.

Once you start getting lean, especially as a professional athlete,  
You should consider using the Body-fat index/percentage instead.

But yeah, you're not the first and probably not the last to tell that person "Calories is Calories".

I've read so many stories when Fat People Hate was a subreddit,  
the amount of folk who'd conveniently forget their super-size Starbucks out of their food diary or not realise how calorie dense oils are and just not count it towards their intake was staggering.

I would like to think that's what the person your replying to really means, but I assume you've seen all the other replies and  
No, it really is denying objective reality, as if people are literally breaking thermodynamics by producing energy, in the form of fats, out of thin air.