The following advice has been provided following consultation with medical experts and Islamic scholars.
Fasting and heartburn
Fasting usually reduces the amount of stomach acid, which digests food and kills bacteria. However, thoughts of food, or the smell of it, make the brain tell the stomach to produce more acid, which can lead to heartburn.
People who regularly take medicine for indigestion - such as antacids, antihistamines or proton pump inhibitors - are advised to continue taking them. A good time to do this could be with the pre-dawn meal.
The control of heartburn or belching can be aided by eating in moderation and avoiding oily, deep-fried or very spicy food. Reducing your caffeine intake and stopping smoking can also help.
Preparations such as peppermint oil may help reduce belching or abdominal discomfort. Sleeping with your head raised on a few pillows, in addition to long-term weight loss, may also help prevent heartburn.
Fasting and poor control of diabetes
People who regularly inject insulin are advised not to fast, as the potential risk to health - both in the short and long term - of not taking insulin is too great. People who have their diabetes under control using tablets should seek careful advice from their GP before starting a fast.
Regular self-monitoring of your blood glucose is strongly advised. Low blood sugar levels (known as a "hypo") are dangerous, and may lead to fainting or fits if left untreated.
Feeling dizzy, sweaty and disoriented may all suggest a hypo. If a person with diabetes has these symptoms, they should immediately have a sugary drink, or place sugar or a sugar-rich sweet below their tongue.
Fasting and a headache
This common problem has many causes. Headaches during a fast could be due to dehydration or hunger, poor rest, or the absence of addictive substances, such as caffeine or nicotine.
A moderate and balanced diet, especially not missing the pre-dawn meal, taking in enough fluids and, if necessary, some painkillers such as paracetamol, can help prevent or reduce the risk of getting a headache.
Headaches can also be prevented by not exposing yourself to direct sunlight, wearing a hat when out, using sunglasses to reduce the effect of glare from the sun and relieving any tense muscles with a short, gentle massage.
Fasting and dehydration
Dehydration is common during a fast. The body continues to lose water and salts through breathing, perspiring and urinating.
If you don't drink sufficiently before a fast, your risk of dehydration increases. This risk is higher in older people and in those taking tablets, such as diuretics.
If you are unable to stand up due to dizziness, or you are disoriented, you should urgently drink regular, moderate quantities of water - ideally with sugar and salt - or Dioralyte or Lucozade.
If you faint due to dehydration, your legs should be raised above your head by others, and when you awake, you should urgently rehydrate as outlined above.
Fasting and constipation
When you are fasting, being active, drinking water regularly and eating healthily (during the times when you are not fasting) will help to keep your bowel motions regular. Include lots of fruit and vegetables in your diet and increase the fibre content of your food using bran. If the problem persists, a short course of laxatives may help.
Fasting and stress
Lack of food and water, changes of routine and shorter periods of sleep can cause stress. It's important to deal with any potential sources of stress to stop any harmful effects. This can be helped by not taking on more than you can handle, not playing sports in the hot sun, controlling your anger and not smoking.
Fasting and weight control
Food consumed during the pre-dawn and dusk meals may lead to some unintended weight gain. However, if you approach the fast with discipline, it can be an opportunity to lose weight and become healthier.
Article provided by NHS Choices