Medical Information
The Skinny on Fasting
Most people in the developed world have never, and will never, go without any food for a single day of their lives - save certain religious traditions or in the case of a really bad flu! But for many people in the poorest nations, hunger is a daily reality, largely made worse by climate change, and it is not one from which they can escape. The Climate Justice Fast stands in solidarity with all those affected by climate change, however our fast is dramatically different from their hunger, precisely because it is voluntary and can end as soon as we choose to end it.
For one-day fasts:
For a normal, healthy person, 24 hours without food should not pose any health risks, provided that they drink lots of water (about 1.5-2L is ideal).
- Do not fast with us if you are on medication or are ill in any way.
- Also, we recommend that you stop taking stimulants such as coffee, sugar and alcohol at least 24 hours before your fast begins. The same goes for red meats and other heavy foods.
- During the 24 hour communal fast, you should only drink water. But drink a lot of it during the day! You should wear warm clothes and keep generally warm and relaxed. You might feel fatigue, nausea or get a headache. It's alright and will go away again.
- The day after your fast you should only eat light food, such as fruits and vegetables. You can combine it with pasta or rice. Go to bed early and get some rest.
No one should fast who:
- Has a history of heart, liver or kidney problems,
- Is pregnant,
- Has any psychological or eating disorder,
- Has recently had surgery,
- Has a history of diabetes, gastric or duodenal ulcers.
For under eighteens:
- Drink plenty of water, fruit juice or tea.
- You can eat an energy sweet, like a barley sugar, every 4 hours.
- If you're at primary school you must NOT skip food for more than 8 hours. When you finish fasting, ease your way back to normal eating by having something light and healthy like a salad or fruit.
- No under-18 should fast more than 24 hours.
Information for longer-term fasts:
The human body is remarkably complex and resilient, and it has evolved to deal with situations of food shortage - up to certain limits. Nearly all religious traditions practice some form of fasting - as a form of mental and spiritual discipline, as penance, or as a form of meditation or prayer. Some people who follow wholistic health practices also undertake regular, short fasts for health reasons, as they are believed by many to have a purifying and detoxifying effect.
It is certain, then, that the healthy, adult human body can very safely go without food for a short period of time - quite a number of days, varying from person to person depending on their personal limits. Prolonged fasting, however, tests those limits, and this page is intended to give an overview of the medical effects of fasting on the human body.
When denied food, the body falls back on its own resources for energy. For the first 4-8 hours of fasting, it uses glucose from the bloodstream. When that is depleted, glycogen stores in the liver and muscles are utilised to produce additional glucose in a process called gluconeogenesis[1].
After approximately 3 days, glycogen is used up, and the body begins using stores of protein from muscles (including the heart muscle) for the production of further glucose. In addition, fat begins to be broken down in a process known as ketosis, which produces fatty acids that can be used by most cells in the body for fuel. This also produces ketone bodies, which are utilised by the brain as a substitute for glucose [2].
After 10-14 days, the body comes to rely mainly on fat stores for its energy, which spares the loss of vital protein [1]. The total amount of stored fat in an individual’s body is the chief determinant of the length of time they can tolerate fasting. In adults of normal weight, fat stores generally permit survival for 2-2.5 months without food, however obese persons have been known to fast for many months and even 1 year [3]. The ten IRA men who died on hunger strike in 1981 survived an average of 61 days, with one dying after 45 days and the other nine surviving between 57-73 days [4].
In the early stages of fasting weight loss generally occurs at the rate of 1 to 2 kg per day, mainly due to a loss of fluids and salt. This rate then gradually declines, reaching an average weight loss of approximately 0.3 kg per day by the third week [5]. In persons of normal weight, serious health problems generally begin with a weight loss of approximately 18% of initial body weight [2], which occurs in most people after approximately 25-30 days of fasting [5,6,7].
A number of medical complications are associated with prolonged fasting. The most common is feeling faint or dizzy due to orthostatic hypotension, which involves light-headedness and even fainting upon standing upright as a result of a decrease in blood pressure [1]. Also common are nausea, headaches, muscle aches, abdominal pain, weakness, fatigue, and cramps [5].
Dehydration is another risk, as individuals tend to lose their feelings of hunger and thirst and may find it difficult to take in fluid. It is important that fluid intake is maintained at an appropriate level (approximately 1.5-2 litres per day, but varying with body size, activity level, and heat). Individuals also often experience feeling cold, which results from hormonal adaptations to fasting [1].
Other complications that can occur in prolonged fasting include: acute gout, which is an inflammatory condition usually affecting the feet that is associated with the elevated levels of uric acid in the blood which occur during fasting, kidney stones, kidney failure (which can be fatal if untreated), edema, which is a swelling of body fluid under the skin that can result from decreased kidney function, atrial flutter, which is an abnormal heart rhythm, amenorrhea, which is the absence of menstrual blood flow in women, and polyneuritis, which is an impairment in the functioning of the peripheral nervous system that can result from vitamin B12 deficiency and lead to muscle wasting and weakness, twitches, cramps, numbness, loss of reflexes and spontaneous pains [5].
Individuals may experience a number of psychological side effects. Early on, after ketosis has begun and hunger pains have subsided, a sense of well-being and even euphoria is quite common. During later stages however, unstable mood, depression, apathy and irritability may all occur [1,2].
Brain damage can also occur amongst individuals who survive extensive fasts. This has been especially prevalent amongst Turkish hunger strikers, who have employed methods of extending the length of hunger strikes dramatically. Ingesting sugar and other nutrients to keep their metabolism going has allowed some Turkish hunger strikers to fast for over 200 days [8].
Generally starvation becomes life threatening when over 30% of original body weight is lost [2]. Hunger strike deaths most often occur as a result of intractable ventricular arrhythmia, which is abnormal electrical activity within the heart that can cause cardiac arrest or instant death. Deaths can also result from kidney failure, complications arising from bowel obstructions, or from lactic acidosis, a condition in which levels of lactic acid within the blood can become fatally high [2,5].
Surprisingly, one of the most dangerous aspects of prolonged fasting (three weeks or more) is breaking the fast, which can itself result in death if handled incorrectly. If the wrong variety or too much food is ingested too quickly a number of serious complications can arise, including electrolyte imbalances leading to heart arrhythmia or failure, Wernicke’s encephalopathy, which is a serious disorder effecting the central nervous system and brain functioning, and hypokalaemia, which is a low level of potassium in the blood that can lead to muscular and respiratory dysfunction. These risks can be avoided by consuming small amounts of food that are high in neither processed sugars or protein, and hospital monitoring is strongly recommended for several days after eating has resumed [1].
Although it is rare, there have been cases in which death has occurred much earlier than expected during fasting, often due to pre-existing medical susceptibilities [5]. This highlights the importance of being aware of the risks of fasting before attempting it, and ensuring that one’s body is capable of withstanding the fasting process.
Prolonged fasting should not be undertaken by pregnant women, nursing mothers, anyone with a chronic disease, history of heart problems, liver problems, kidney problems, anemia, eating disorders, psychological problems, or currently on any kind of medication. Prior to fasting, it is strongly recommended that individuals undergo at least an electrocardiogram to ensure the satisfactory function of the heart, and basic tests of liver and kidney function, and they should generally be personally confident that they are in good physical and mental health. Talking to a counsellor may be recommended if you are unsure. During fasting, it is recommended to regularly have bodily electrolyte levels tested, as imbalances can cause cardiac arrhythmias, which are the major risk of medium-long term fasts.
It is also strongly recommended that individuals wishing to undertake a prolonged fast lead up to it with shorter fasts of increasing length. Although the barriers against starting with a long fast are psychological rather than physical, most people that fast for long periods find it necessary to begin with fasts of shorter duration.
An interesting and useful resource for anyone considering undertaking a fast are the numerous internet forums devoted to fasting, in which people who have undergone prolonged fasting share their experiences. Three of these are: here , here and here.
Our understanding of prolonged fasting is incomplete, and based on very few observed cases. The above information is not intended as a substitute for medical advice, it is simply an attempt to briefly summarise the general medical understanding of fasting as it stands to date. If you are considering fasting, seeking medical advice is advised, yet it must be remembered that normal GPs will very likely be quite limited in their knowledge of fasting, and will often refuse to give medical advice on the subject. Before coming to a decision about fasting, individuals are encouraged to pursue their own research as well.
[1] Peel, M. (1997) Hunger Strikes: understanding the underlying physiology will help doctors provide proper advice. British Medical Journal 315 (7112), 829-830.
[2] Crosby, S. S., Apovian, C. M., Grodin, M. A. (2007) Hunger strikes, force-feeding, and physicians’ responsibilities. JAMA 298 (5), 563-566.
[3] Cahill, G. F. (1998) Survival in starvation. American Journal of Clinical Nutrition 68 (1), 1-2.
[4] Altun, G., Akansu, B., Altun, B. U., Azmak, D., Yilmaz, A. (2004) Deaths due to hunger strike: post-mortem findings. Forensic Science International 46, 35–38.
[5] Kerndt, P. R., Naughton, J. L., Driscoll, C. E. (1982) Fasting: the history, pathophysiology and complications. Western Journal of Medicine 137, 379-399.
[6] Frommel, D., Gautier, M., Questiaux, E., Schwarzenberg, L. (1984) Voluntary total fasting: a challenge for the medical community. The Lancet 8392, 1451-1452.
[7] Faintuch, J., Soriano, F. G., Ladeira, J. P., Janiszewski, M., Velasco, I. T., Gama-Rodrigues, J. J. (2001) Refeeding procedures after 43 days of total fasting. Nutrition 17, 100-104.
[8] Sengupta, S. Turkish hunger strikers risk body and mind, The New York Times, Tuesday December 18, 2001 http://www.nytimes.com/2001/12/18/world/turkish-hunger-strikers-risk-body-and-mind.html last viewed at 5PM 11/05/09
