How Fasting Affects Your Health

By , SparkPeople Blogger
Many religions recommend fasting for both spiritual and/or health benefits. All religious fasts are different: Some restrict certain foods, while others only restrict the times of day in which one can eat. Few religious fasts involve a long-term or complete abstinence from food, but no matter what the nature of the fast is, you may wonder just how it really impacts your health.
Three religious fasts have been studied the most:
  • Islamic Ramadan: During the holy month of Ramadan, which varies according to the lunar calendar, Muslims abstain from eating or drinking from sunrise to sunset.
  • The 3 annual fasting periods for Greek Orthodox Christians:  The Nativity Fast (40 days prior to Christmas), Lent (48 days prior to Easter), and The Assumption (15 days in August).
  • Biblical-Based Daniel Fast:  This fast typically incorporates a 21-day fasting period.
Read on to find out how these fasts impact your health and weight-loss efforts.


During the holy month of Ramadan, all healthy adult Muslims are forbidden from consuming any food or water from sunrise to sunset. It is a common practice to eat one large meal after sunset and one lighter meal before dawn.  While many people that Ramadan fasting leads to reduced calorie intake and weight loss, recent studies have found that for many of the participants actually eat more calories during Ramadan because the two meals often contain higher-fat foods than their typical (non-fast) diet.
Ramadan fasting may impact the clinical markers for heart health, but research results have been mixed.  Some studies have found improvement (an increase in the healthy HDL levels and a decrease of the "bad" LDL levels), while other studies discovered the exact opposite. Some research found that blood pressure and resting heart rate decreased in Ramadan participants, while other studies found no difference.   The same can be said about the studies evaluating blood sugar levels during Ramadan.  Some studies showed improvement while other studies found no effect. 
It appears that Ramadan may have a negative impact on sleep quality, decreasing slow wave sleep and rapid eye movement (REM) sleep.  This lack of quality sleep has been shown to result in irritability and an increase in caffeine intake using coffee and tea. 
Ramadan fasting can also increase gastric secretions and overall gastric acidity throughout the day, which could lead to ulcer complications.  Other potential adverse health effects associated with Ramadan fasting include energy level imbalances, dehydration, decreased athletic performance, and altered circadian fluctuations in hormone levels.
Changes in food choices, eating habits, physical activity, and sleep routines are all variables that could be impacting one’s overall health during the Ramadan fast.  Being aware of how these changes impact health is crucial.  It may be necessary to have a larger, hearty meal before sunrise, thus providing the calorie-providing energy for daily activities or light exercise.  A lighter evening meal would be less taxing on the stomach, less time to prepare and allow for better sleep. Total food intake for the day should be geared toward meeting calorie and nutrient needs.

Greek Orthodox Fasts

There are three principal fasting periods for Greek Orthodox Christians. Each fasting period has a slightly different food composition.
  • During the 40 days that precede Christmas (Nativity), dairy products, eggs, and meat are prohibited every day, while fish and olive oil are also forbidden on Wednesdays and Fridays.
  • During the 48 days that precede Easter (Lent), dairy products, eggs, and meat are forbidden.  Olive oil consumption is permitted only on weekends during this period, and fish consumption is only allowed on March 25 and Palm Sunday.
  • During the first 15 days of August (the Assumption), dairy products, eggs, and meat are prohibited. Olive oil consumption is permitted only on weekends during this period, and fish consumption is only allowed on August 6.
  • Cheese, eggs, fish, meat, milk, and olive oil are also prohibited every Wednesday and Friday that falls outside of the principal fasting periods. This latter proscription is temporarily lifted on the week following Christmas, Easter, and the Pentecost. Collectively, dietary consumption is restricted in some way for 180-200 days each year.
Most research studies have reported that participants consume fewer calories during these fasting periods, which can result in weight loss for some people. However, because people are eating less meat and dairy, their carbohydrate and fiber intake increases while their calcium, protein, fat, saturated fat and trans-fatty acid intake also decreases, usually resulting in a decrease in total cholesterol and LDL levels.  The fasting periods have not been shown to lower blood sugar levels, nor was there a change in hemoglobin, serum iron or transferrin levels.  
Because these fasts go on for so many days, participants may want to include a calcium supplement to make up for their reduced calcium intake.

Daniel Fast

The Daniel fast is based on the Biblical story of Daniel in which Daniel resolved not to defile himself with the royal food and wine. He and his three friends ate nothing but vegetables and water for 10 days.  Later Daniel partook in a 21-day period of "clean" eating, during which time he ate no meat or wine.
Based on these two fasts by Daniel, a modern day Daniel Fast involves unlimited intake of fruits, vegetables, whole grains, nuts, seeds, and oil.   This fast if very similar to a vegan diet (no animal products) but is stricter, because all refined carbohydrates, preservatives, additives, sweeteners, flavorings, caffeine, and alcohol are also forbidden.
In the literature, excellent compliance has been noted with the Daniel fast as well as improvement in mood and feelings of fullness.  Many health variables have shown to improve, including total cholesterol, LDL, blood pressure and blood sugar.  Body weight and body fat improved slightly but were not statistically significant. 
It is not the intent of this article to dismiss any religion or religious fasting practice. As already stated, limited data is available for other forms of religiously motivated fasts.  The impact of religious fasting on one’s weight and health remains an area for warranted research.
Most healthy adults can safely fast for one day and their bodies will be able to adjust, drawing upon energy and nutrient stores. However, always check with your physician regarding how fasting will affect your medical conditions, medications, and health history. Certain disease conditions may warrant against fasting altogether. You should also discuss with your doctor the specific danger signs and symptoms that would indicate the need to stop the fast, such as dizziness, lightheadedness, inability to focus or concentrate, blurred vision, heart rate changes, etc. Talking with your religious leaders can help you determine an appropriate fasting option to meet both your medical needs and religious commitment.

Celik A, Saricicek E, Saricicek V, Ozdemir G, Sahin E, Bozkurt S, Okumus M, Sucakli MH, Cikim G, Coskun Y, Deniz MS, Dogan E, Kilinc M. Effect of Ramadan fasting on serum concentration of apelin-13 and new obesity indices in healthy adult men.  Med Sci Monit. 2014 Feb 28; 20:337-42.

Mehta LH, Roth GS.  Caloric restriction and longevity: the science and the ascetic experience. Ann N Y Acad Sci. 2009 Aug; 1172:28-33.

Pamplona R, Barja G.  Mitochondrial oxidative stress, aging and caloric restriction: the protein and methionine connection.  Biochim Biophys Acta. 2006 May-Jun;1757(5-6):496-508.
Trepanowski J, Canale R, Marshall K, Kabir, MM, Bloomer R.   Impact of caloric and dietary restriction regimens on markers of health and longevity in humans and animals: a summary of available findings.  Nutr J. 2011; 10: 107.

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ERIN_POSCH 1/8/2021
thanks for sharing Report
ELRIDDICK 10/18/2020
Thanks for sharing Report
Very interesting read! It leads to some understanding which is greatly lacking in today's society. Report
interesting infio Report
I'd dearly love an updated, more inclusive and diverse SP article that notes Judaism (several fasts as well as Yom Kippur) Buddhist, and Baha'i fasts as well.
Might be nice to speak to some religious leaders as well as doctors to give some medical and spiritual solidity to this piece. Thanks! Report
Ummm I think some people here sound like they have never fasted themselves, all - it is an act of faith, particularly for the (glaringly absent) example of Yom Kippur (Day of Atonement) that Jews and Messianic Christians observe. So sure, "either you are healthy or you are not" - that kinda goes without saying. But for one who is stepping out in faith that they believe they should be fasting on a spiritual and physical level, that's why a person with diabetes or other illnesses might want to chat with their Rabbi or Pastor (for the Messianic types) about what to do. Most of my friends or relatives that I know who are diabetic etc, they prepared in advance - whether during the month before or a week or two, even a few days before, to modify their sugars and carbs and took on extra water in the days before. Some of my friends are coffee junkies (which yea, probably isn't the healthiest habit) will wean off a week before so as to not be all headachey or ill during the Fast days.

(as a side note, "Religious leaders are not doctors..." that's not always true. In the Christian traditions, the Priests in the Old Testament were the ones who would examine individuals for communicable illnesses. There are other examples of healing treatments using herbs, oils, etc discussed in the Bible, all thousands of years pre-AMA {American Medical Association, etc} or other organized medicine groups...midwives etc etc. and in some congregations, that dual-role of spiritual leader/medical healer etc has continued through history, as people do become certified medical doctors and also are chosen or selected or inherit spiritual leadership positions within their specific congregation, mosque, synagogue whatever. Just a thought.).

We believe the Creator already knows our needs, as He created our bodies and He created fasting as a period of time where the body can redirect its energies towards healing and detoxing. There is a definite mind-body-spiritual component to the fasting process, and the body does not panic the same way that starvation does. Even now, doctors have noted benefits in "intermittent fasting" as a way to improve the body's health, whether losing weight or other issues.

The Daniel fast is an excellent way to test the waters, so to speak, if one has never fasted before in their life. The Ramadan fast, of course I have never done, but some of my Muslim friends have told me they did better ending the fast with less food and saving some of the richer foods to eat in the pre-dawn feeding. That way they could sleep better and the extra food in the predawn feeding helped them sustain the daytime fast, especially those years when Ramadan slides around so that it lands during the longer summertime hours. But I can't speak for "all" Muslims, I'm just merely repeating what some had told me (fellow students at college etc.). I also have a friend who does the Greek Orthodox fasts and he says he feels better after doing them, but I'm not exactly sure what he does for his protein etc, since there seems to be a (confusing, to me) group of instructions about what they can and can't eat during those days.

So don't panic, don't knock fasting until you have tried it. Report
You say the religious fasts are for healthy adults, then at the end of the article, you say that you can talk with your religious leaders about how to do the fasts with your medical condition. Hey, either you are healthy or you are not! If you are not, you DO NOT have to do the fast! Religious leaders are not doctors, and are not qualified to give medical advice of any kind. If you feel that your condition will get worse with fasting, please don't do it. Why even ask the doctor if it's okay? Just enjoy eating normal food. Fasting will impact your health, and is not for ill people. Report

Really interesting. I'm Greek Orthodox and my Muslim friend and I would regularly compare the onerousness of having to go virtually vegan, full time vs a sunlight fast, that also incorporated liquids - which we never resolved but supported each other through with laughter, definitely!

I have to say, though, somehow the Lent fast while working full time in the UK saw me put on weight every time. There's so much healthy protein you cut out, and so much that is time consuming to prepare, it can be hard to choose the healthiest options on this fast, I find... Report
We fast once a year at the very least, on Yom Kippur (Day of Atonement ) - which is no food, drink, water, alcohol, nothing for basically 24 hours - sunset to sunset. As little kids, we thought we would die and were cautioned against drinking water too fast at breaking the fast. Some would forget and just drink and eat too quickly and end up with upset stomach, but we'd learn and next year do better. We are encouraged to do other fasts during the year, either a 24 hour no food no water no drink like Atonement or other modifications like a Daniel type fast, depending on what our physical and spiritual needs are. I've had diabetic friends who have discussed with the spiritual leaders what they "should" or "could" do for the fast and most try to prepare in advance by weaning back on coffee or sugary foods a few days to a week before, so as to lessen potential impacts like "caffeine withdrawal headaches" when they do fast. Or some will prepare small amounts of foods that will help them stabilize their blood sugars as needed, but largely fast for as long as they are able. Report
I fast on Fridays, I don't know how to log it into my food, all I have all day is nutriblasts until dinner. Report
Excellent article. Our church does an annual Daniel Fast. Report
I have done the Bahai Fast for many years and it consists of no food or drink from sunrise to sunset from Mar. 1 to Mar. 20th. It has never really affected my weight because usually I would lose about 5 lbs. during the fast and then put it back on gradually. I found that trend to be true among Bahai friends too. Report
Hi! As an Orthodox Christian, I felt I couldn't let the opportunity pass to comment on this wonderful article. Controlling food intake is a powerful tool in spiritual practice. What we Orthodox call "fasting" as the article states, is not the same as refraining from eating. We just want to be mindfully in control of our food choices. We want the mind to dictate to the stomach and to the eyes.
Mindful living, informed choice, healthy bodies and healthy minds. Pretty much what we all want? Report
I liked the Daniel fast idea as well. Even if you don't lose much weight, at least you will be super healthy! Report
I found that really interesting, I like the Daniel fast idea! Report