Explained scientifically: Fasting makes you happy!

Most people who have undergone F.X. Mayr Therapy know what we're talking about: a long-lasting "high" and more energy than you ever dreamed possible – not merely because the kilos melt off and you feel lighter in general:

In F.X. Mayr Therapy (as with therapeutic fasting in general), the metabolism changes from sugar- to protein-based. This means, after a certain amount of time your brain does not draw its energy from the sugar and carbohydrates you have eaten, but rather from your fat reserves. The transitional phase between the two is sometimes associated with forgetfulness, known as "fasting brain", as your body learns to tap into different resources. 
However, as soon as the ketones produced by protein and fat metabolism begin entering the brain, things improve rapidly. Ketones impact the structure of synapses (neural connectors) very positively, promoting learning processes, memory and the health of the brain in general. Furthermore, the protein BDNF (Brain-Derived Neurotrophic Factor) is produced, which strengthens the synapses, stimulates formation of new nerve cells and even has anti-depressant effects.
Experiments with animals have shown that fasting can also help to suppress age-related degenerative processes within the brain, thus potentially preventing neurodegenerative illnesses and dementia.

Fasting doesn't only have antidepressant effects because of the proteins that are formed, but might also be able to combat the reasons that cause a depressed state of mind: Researchers have long conjectured that the immune system has a major influence on mood.
Scientific studies have confirmed that inflammatory messenger substances (so-called pro-inflammatory cytokines) negatively impact mood, disrupt concentration and cause fatigue. Stress results in more of the substances being produced, the consequence being mild chronic inflammation. Because many patients coping with depression also present higher inflammation levels (cytokine concentration) in their blood, it is presumed that they do indeed impact development of this condition.

Much research in recent years has confirmed what Dr. F.X. Mayr basically knew 100 years ago: the intestines play a very important role in our health, not least because most of our immune system is based there. If our intestines are not healthy, our overall condition will be poor – not just in the belly, but throughout the body and, above all, in our brain.

Read more: depression, Parkinson's, autism – conditions affecting the brain begin in the intestines.

Sources & Further Studies:

3-Hydroxybutyrate regulates energy metabolism and induces BDNF expression in cerebral cortical neurons   

Nutritional strategies to optimise cognitive function in the aging brain. 

Intermittent fasting attenuates lipopolysaccharide-induced neuroinflammation and memory impairment. 

BDNF mediates adaptive brain and body responses to energetic challenges.  
 
John Hopkins Health Review: "Are There Any Proven Benefits to Fasting?", Spring/Summer 2016 Volume 3 Issue 1.