Can you eat junk food and lose weight?

YES.

Is it healthy, no, but it can be done

Which is always a kicker for the clean eating movement, eating good wholesome food alone isn't enough, you need to eat less than you can burn

So what's the best way?

Eat good healthy food and eat less than you burn for optimal fat loss

and the same goes for weight gain, eat a bit more to give your body the fuel it needs to grow

We know the science of fat loss, what is more ambiguous is the role or path for optimal health, which is always up for debate

one reason I recommend you eat as much nutrient rich food as possible, eating less optimal food occasionally i.e. When your out with friends for food or drinks

The guy featured on this post eats one meal a day of 4000 calories of junk food, again it can be done, but it doesn't mean it's healthy or optimal