If this turns out to be completely true being able to harness it and teach it to others would help a great deal with world hunger.
Living without food for 15 days isn't a pleasant undertaking by any means, but it's perfectly doable. It's the water that's impressive, if true, but world drought sounds a lot less threatening.
Photosynthesis, or pure Mental Will?
Lack of chloroplasts, plus it would kill you faster even if you could. Photosynthesis consumes water.
Imagine if Food and Water became a luxury, and not a necessity. ;)
Highly unlikely, even assuming that the study is true. Even if you meet your daily caloric intake needs, you can still suffer from malnutrition if you don't consume enough of key elements or biomolecules that your body can't synthesize de novo--scurvy is probably the best known example. Even if this guy was hiding a glucose IV drip, that wouldn't be enough to keep him healthy and alive.
In the Stone Ages there was not Vitamins and Minerals in abundance via Foodstuffs. Everything was limited at best. So how did they live?
With abundant starvation and unequal distribution of resources.
Well we all know several things that cause the body to age and the basic element to make us go. Hydrogen
Hydrogen is about as biologically useful to animals as helium.
The Ozone back then was far more intact. Pollutants were nil and the greatest stress we had was getting eaten. So how was it that our ancestors lived back then without the basic supplimental elements we have to have now? Theory: Hydrogen Synthesis After all it was incredibly abundant back then what if we really were able to do just this. What if this is what this Yogi figured out?
Synthesizing hydrogen would require decomposition of water or other perfectly useful biomolecules. This would just kill you faster, even if it was possible.
Now, assuming that this study is true, one extremely unlikely explanation would be that his body accelerated its metabolism rate to generate water. I don't recall the exact numbers, but I remember seeing somewhere that the human body generates on the order of 30% of its total water needs with cellular respiration.