We looked recently at rare twin pairs containing one depressed twin and one happy one. In the affected twin’s blood we found altered levels of the key brain chemical serotonin. This chemical comes from our food except when we are fasting, when our gut microbes manufacture it for us. So changes in our microbes will alter this key brain chemical and, potentially, our mood. This could explain the odd sensations of a euphoric high reported by some people after fasting.
