A difference in the alkalinity (electrical conductivity) of the food you're eating. Raw foods have a grounding effect, quite literally. The body functions better at a slightly alkaline tilt (negative electrical charge) than at an acidic tilt (positive charge)

Food processing tends to change the nature of the nutrients in foods, such as heat deactivating enzymes naturally present in the plant, as well as killing the probiotics that exist on the foods. Vitamin C is a classic example, losing over half of its potency in Orange juice after pasteurization, and by exponents, the remaining potency over its shelf life.

Dr Jerry Tenant explains it nicely on YouTube.
http://www.youtube.com/playlist?list=PL9794323F5BEC78C0
(Skip first video if not familiar with rife and zapper technology, each playlist video is 9min 51 seconds, explanations given in detail.)

Oxadative stress happens both in the brain and below the brain, especially in the digestive track.. Oxadative stress is another name for an electrical imbalance in the body.

The ph scale is a way to measure the electrical value of a given medium, be it water, metals, etc.
Alkaline = negative charge
Acid = positive charge

Both alkaline and acidic compounds in raw food contribute to health, so don't confuse the ph scale for how to measure what you eat, at least not in the direct sense.