Your body is very good at leveraging osmosis to move water around. It's main goal is to maintain adequate volume in your circulatory system (low volume means low pressure, just like any pumping system, low pressure means not enough blood gets to your brain). It will shift fluid around from various places to keep enough in the blood. This effect is actually leveraged in traumatic injuries with significant blood loss. "Extra" salty water will be given via IV, and that will 'pull' water into the circulatory system, via osmotic pressure.
If you're peeing out the water you drank within an hour or two, it's because your body didn't need it (or it needed to use it to carrying some stuff out with it). Urinating is a _good_ thing.
What suprises me is that anyone with knowledge in physiology would call this study "brilliant". I would expect better of someone leading a laboratory and an education in biology. (http://kins.uconn.edu/lawrence-e-armstrong-ph-d/)
That is... as _long_ as you constrain yourself to only concluding the facts that are there. How fast your stomach empties and urination schedules ... these aren't facts the average person can draw any conclusions from.
Good for science, bad for stupid news articles.
Are you more "hydrated" if your stomach is carrying around fluid for longer?
They test how much healthy young men pee out 2 hours after consuming something. The problem is, it's a dumb test. That 2 hours is pretty short when it comes to how long it takes things to empty from your stomach. With a full meal, your stomach would be a little more than half full at that two hour mark.
Just water gets dumped from your stomach really quickly, 50% in 10 minutes. Here's the rub... while it might not be sure based on the study design, it seems there's a real good chance that the only thing going on here is people carry milk and pedialyte around in their stomachs longer. That's it. No extra "hydration" no health benefits.
It would be akin to saying drinking 1L of water right away is more hydrating than drinking it in small increments over 2 hours. Is it more hydrating? Or did your body just have less time to turn it into urine?
The big assumption being made is equating "hydration" with how much fluid you didn't pee out after two hours. If it's not tied to some set of health metrics (and really if it isn't tied to a long term health study) it should say absolutely nothing about conclusions an average person should take.