Fad means you lose an insane amount of weight very quickly....the negative is you gain it back just as fast.
Exercise can help stabilize but according to this thread exercise is frowned upon
tho I think that is why you see Hulk keep steady. Despite some binge days, he has increased his metabolism enough to sustain.
You'll hear the argument that it is not a fad; rather a lifestyle change. While ill admit no diet is fool proof, I think the sample size from this thread proves that Atkins' long term sustainability is in question.
Example: "oh I'm fat, I need to lose a bunch of weight. Ill try Atkins."
....6 months later....
"Ok, I've lost 50lbs, I'm going back to the way I used to eat"
.....1 month later
"Holy crap, I've gained 15lbs!!!!! Better go back to Atkins to lose some weight quickly again!"
That's a fad. The draw is you lose weight very quickly, & the game plan to do it is very relatable.
To put it in perspective someone is using it in a weight loss challenge. Where most people would exercise hardcore and eat lean, your go to move is a fad diet. That really says it all.