Comment by baran

With that said, for the majority of the healthy population, the main indicator of health is weight. Thus for the personal health space, the holy grail is a device which automatically measures the caloric input/output. When I say automatic, I really mean automatic. No writing/taking pictures/tweeting about your food or exercise. Think a watch that tells you how many more calories you can eat in the day. Anything more complicated will fail.

Aza does point out an example population which would be assisted by better technology - individuals with chronic health problems. These people are faced with their disease everyday, whether they want to think about it or not, so they have the most to gain from new technology. There is a niche in improving the "diabetes diary", but in my mind the real power comes from a complete feedback loop. One which encourages care providers (physicians, nurses, etc.) to be more involved in managing their conditions. Think about giving your diabetes diary to your physician. Patterns would emerge for the physicians that would not be seen by the patient. This data could then be the catalyst for change in how the patient manages their disease.

The problem right now is that no personal health system exists with connects patients and providers. The data which resides in your medical record is locked into proprietary systems which are vary reluctant to "open" data. However, the landscape is beginning to change. Industry is realizing a the game-changing health applications need the underlying data which is being housed in clinical institutions to function optimally. Check out SMArt Platforms if your interested in this push.

Summary

Be very careful in the personal health space. Two things I've learned after being in the industry for a while (1) it's very difficult to get people to care enough about their health to take action on it and (2) the most useful applications are the ones which connect patients and care providers which is difficult due to lack of data liquidity.