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neurotrophic factor. BDNF has been shown to stimulate stem cells to turn into new nerve cells in the hippocampus. As I mentioned earlier, this is a part of the brain that is essential for normal learning and memory.
    But why should the hippocampus grow in response to fasting? Mark points out that from an evolutionary perspective it makes sense. After all, the times when you need to be smart and on the ball are when there’s not a lot of food lying around. ‘If an animal is in an area where there’s limited food resources, it’s important that they are able to remember where food is, remember where hazards are, predators and so on. We think that people in the past who were able to respond to hunger with increased cognitive ability had a survival advantage.’
    We don’t know for sure if humans grow new brain cells in response to fasting; to be absolutely certain researchers would need to put volunteers on an intermittent fast and then kill them, take their brains out and look for signs of new neural growth. It seems unlikely that many would volunteer for such a project. But what they are doing is a study where volunteers fast and then MRI scans are used to see if the size of their hippocampi changes over time.
    As I mentioned above, these techniques have been used in humans to show that regular exercise, such as walking, increases the size of the hippocampus. Hopefully similarstudies will show that two days a week of Intermittent Fasting is good for learning and memory. On a purely anecdotal level, and using a sample size of one, it seems to work. Before starting the Fast Diet, I did a sophisticated memory test online. Two months in I repeated the test and my performance had, indeed, improved. If you are interested in doing something similar then I suggest you go to www.cognitivefun.net/test/2. Do let us know how you get on.

Fasting and mood
     
    One of the things that Professor Valter Longo and others told me before I began my four-day fast was that it would be tough initially, but that after a while I would start to feel more cheerful, which was indeed what happened. Similarly, I was surprised to discover how positive I have felt while doing Intermittent Fasting. I expected to feel tired and crabby on my fasting days, but not at all. So is this simply a psychological effect, that people who do Intermittent Fasting and lose weight feel good about themselves, or are there also chemical changes that are influencing mood?
    According to Professor Mark Mattson, one of the reasons people may find Intermittent Fasting relatively easy to do due to its effects on BDNF. BDNF not only seems to protect the brain against the ravages of dementiaand age-related mental decline, but it may also improve your mood.
    There have been a number of studies going back many years that suggest rising levels of BDNF have an antidepressant effect, at least in rodents. In one study, they injected BDNF directly into the brains of rats and found this had similar effects to repeated use of a standard antidepressant. 10 Another paper found that electric shock therapy, which is known to be effective in severe depression, seems to work, at least in part, because it stimulates the production of higher levels of BDNF. 11
    Mark Mattson believes that within a few weeks of starting a two-day-a-week fasting regime, BDNF levels will start to rise, suppressing anxiety and elevating mood. He doesn’t currently have the human data to fully support this claim, but he is doing trials on volunteers which involve, among other things, collecting regular samples of cerebrospinal fluid (the liquid that bathes the brain) in order to measure the changes that occur during intermittent fasts. This is not a trial for the faint-hearted as it requires regular spinal taps, but as Mark pointed out to me, many of his volunteers are already undergoing early signs of cognitive change, so they are extremely motivated.
    Mark is keen to study and promote the benefits of Intermittent