(1) A general "naturalistic fallacy" where the author believes that people of the past must have been more healthy.
(2) I assumption that there is an increase of cancer in modern age solely because of humans change of diet - ignoring factors such as environmental pollution, ozone depletion, increase in radioactive particles from weapons testing and accidents...
(3) Assuming that a change in mean is brought about by changes in every individual to the same degree. Differences in the mean can be produced by just a subset, even a minority of outliers. Today, many people are overweight, which is known to increase all kinds of risks. So caloric restrictions applied to the whole society will always cause a rise in mean life expectancy. But that doesn't mean that it will have any benefits for the people who aren't overweight.
(4) Confuses brain size with brain function. I guess the author then must also believe that women are significantly more stupid then men. Also fails to explain that people can sometimes lose a big chunk of their brains and still perform well on tests.
Again, I'm not saying fasting is bad, but that the author just throws together some unrelated scientific studies with a bunch of common fallacies (and, it seems, bias towards his own lifestyle choices).
This one is wrong. People without big chunks of brains are significantly worse than their peers. I vaguely remember that none of them ever had IQ > 100.
Sorry but I honestly stopped reading there. While there is nothing wrong with theorizing. This feels like "do your own research"