Quick science lesson: You know when you add water to chia seeds and it forms into a gel? Well, that glob happens when H2O molecules layer upon each other, which is what forms that slimy substance. That slime is actually called “structured” or “gel” water, known by some experts as the fourth phase of water, as it exists in between solid and liquid. 

“It is in that form that’s found in nature, and it’s also in that form that’s found within our cells,” Cohen adds, which is precisely what makes the gel so hydrating. (Note: You can also find gel water in cucumber seeds, which is what makes them star hydrators, too.)

Chia seeds are also full of fiber, which is why they can absorb up to 10 to 12 times their weight in water. “The fiber is what really acts as a sponge,” Cohen notes. In fact, she tells us that her co-author, cultural anthropologist Gina Bria, suggested her mother (who was suffering from overt dehydration) put chia seeds in her orange juice every morning. “She never became dehydrated again, because it held onto the hydration better,” Cohen recounts. Of course, this is no clinical trial—just one person’s success story—but the science behind it makes sense. 

There’s also some anthropological evidence at play here: The Tarahumara tribe of Mexico, known for their incredible endurance running skills, frequently drink chia seeds with their water, as award-winning journalist Christopher McDougall reported in his ethnographic work, Born To Run

“They would run these 50 mile marathons with chia seeds,” says Cohen, a beverage known as iskiate. “It’s the chia seeds that are holding on to that hydration much better than just plain bulk water alone,” she adds. 

https://www.mindbodygreen.com/articles/why-chia-seeds-are-stellar-for-hydration