Normally our bodies and of course our brains, are fuelled by the glucose (in the form of glycogen) that we obtain from the foods we eat. When we fast for periods greater than 12 hours, there is a ‘metabolic switch’ as our neurones now rely on an alternative energy source called ‘ketone bodies’. Most days, I always try to keep at least 12 hours between the time I have dinner in the evening to the time that I have breakfast in the morning. This can be achieved, for example, by finishing dinner by 8 pm at night and then having breakfast in the morning at 8.00 am (the so called 8,8 regime). There is of course nothing wrong in changing this to 7 pm for dinner and 7 am for breakfast OR 7.30 pm for dinner and 7.30 am for breakfast. The important thing is that you maintain this minimum of 12 hours of fasting. On weekend, I will often extend my fasting time to around 14 hours, as I won’t have breakfast until I return from taking my dogs on a longer walk in the morning.