Fasting is an important spiritual aspect of many religions, such as Islam, Hinduism and Judaism. As well as the abstinence from food (and sometimes drink), fasting is also usually a time of prayer, reflection and purification. It is an opportunity for people to adapt to a healthier lifestyle by learning self-control and making changes to their diet.

There is also the danger of the blood glucose level becoming too high when normal levels of medication are not taken. This can lead to diabetic ketoacidosis (DKA), a condition requiring hospital admission. The symptoms of DKA include feeling very thirsty and passing a lot of urine. If someone is fasting and does not take in fluids to reduce their thirst, this will accelerate dehydration and they will require urgent admission to hospital.