Biochemically, once you have not consumed anything for around 12 hours you are fasting (ie your liver is out of sugar and you are shifting to ketosis). So reall

Biochemically, once you have not consumed anything for around 12 hours you are fasting (ie your liver is out of sugar and you are shifting to ketosis). So really it depends on your definition of fast, but scientifically skipping breakfast pushes you to the definition.