What you weigh on one day isn't a gain/loss, it is just naturally going up and down. 1,500 calories of starch and carbs might impact your water retention or bloating by more than 4,000 calories of protein, fat, and veggies. So yeah, it might in the very short term, as in the next couple of days, impact what the scale says. But it doesn't have a different impact on what you weigh long term. Quality of what you are eating will impact how full you feel and your overall health. Your biometrics will be different based on what calories you take in. But at the end of the day calories are calories when it comes to weight gain/loss..
Bullcrap. Yeah, I know what water gain is.
You know what, I have been working with a lipidologist for almost 10 years. My diet/nutrition plan has been tweaked, medications tweaked, exercise has been tweaked off and studied. A few years ago my case history was published in several medical journals in regards to lipids, so I think I have a clue about how my body works. If you don't believe me, talk to her. http://www.taradall.com
With 100% certainty, I can tell you as a TriAthlete and weightlifter, I cannot eat carbs like most of them do and "maintain", I gain weight over the long term, and all kinds of indicators go wrong.