Many Jewish readers will be looking forward to a healthy breakfast this morning after the 25-hour fast of Yom Kippur which ended just after sunset yesterday. Although fasting is a part of many religious traditions, the evidence for its effect on the brain is mixed.
What does seem clear is that calorific restriction (through fasting, the 5:2 diet or just eating less) is one of a familiar set of interventions that can help to keep your brain healthy. Along with physical exercise and intensive mental activity, fasting seems to increase the production of a helpful chemical called BDNF (brain-derived neurotrophic factor) which supports the formation of new connections and even new brain cells. It is one of a range of responses to mild stress that ends up making you stronger.
In terms of religious fasting, little official data is available, but anecdotally people often eat so much in the meal immediately before the fast begins, and in the one just after it ends, that the total calorific intake for the overall period is about normal. So even while the spiritual significance is clear, it may not bring the medical benefits you hoped for.
Dr Daniel Glaser is director of Science Gallery at King’s College London
