Fasting, particularly intermittent fasting, has skyrocketed in popularity. This simple, yet effective way of eating has been praised for its many health benefits. From weight management to improved gut health, fasting appears to promote health and wellness which may even lead to an increase in longevity. Let’s explore the many forms of fasting and examine the research surrounding the advantages of this wildly popular diet trend.
The History of Fasting
Fasting is the act of willingly abstaining from eating and/or drinking for a period of time. A fast can vary in duration and frequency and may include some food or drink depending on the type.
Fasting can be traced back to the 5th century, when Greek physician Hippocrates recommended abstinence from food or drink for patients with certain health conditions. Other physicians throughout history have acknowledged the link between illness and loss of appetite and believe that eating when sick can be unnecessary and even harmful.1
As a healing tradition, fasting is often touted as “the physician within”, allowing your body to reduce the energy needed for digestion, which can further promote healing from an infection.
In fact, one 2016 study examined the effects of fasting on different illnesses and found that fasting may be beneficial when trying to ward off a bacterial infection.2
We also see fasting throughout human history as many cultures and religions practice fasting for spiritual purposes. For example, many practicing Muslims fast from sunrise to sunset during the holy month of Ramadan, while Yom Kippur, is just one of the fasts that are a part of the Jewish religion.
Forms of Fasting
There are a variety of fasting methods but most types of fasts are implemented over a period of 24 to 48 hours. Intermittent fasting (IF) involves switching between periods of eating and fasting, ranging from a few hours to a few days at a time.
The following are different forms of fasting:
Time-restricted intermittent fasting
This type of fasting involves fasting every day for 12 hours or longer and eating in the remaining hours. One example is the 16:8 method in which you fast for 16 hours and then eat within an 8-hour window, for example between 10 am and 6 pm.
Twice-a-week method
Twice-a-week method, also known as the 5:2 diet involves eating normally for 5 days of the week and then restricting your intake to approximately 500 calories on the remaining 2 days.
24-hour fast
The 24-hour fast, also known as the eat-stop-eat method, involves a 24-hour fast once or twice each week.
Alternate-day fasting (ADF)
Alternate-day fasting involves fasting one day, and then eating what you want the following day. Many people practice a modified version of ADF which enables you to eat approximately 500 calories on your fasting day. This modified version is likely more sustainable than doing a full fast.
Multiple day (48 hour) fasting
During a 48-hour fast, you abstain from eating for 2 full days while drinking plenty of calorie-free fluids like water, coffee, and tea to help prevent dehydration.
After 48 hours, it’s important to slowly reintroduce solid foods to prevent overstimulating your gut which can lead to nausea and diarrhea. This type of fast is generally done 1-2 times per month.
It is important to note that going more than 48 hours without food can be harmful and may even promote fat storage in response to fasting for a longer time period.
Benefits of Fasting
A large number of studies have shown that fasting, particularly intermittent fasting may carry with it a wide range of health benefits. Researchers theorize that fasting places cells under mild stress. While significant stress can be damaging, mild stress encourages cells to adapt, which can enhance their ability to cope with stress and possibly resist certain health conditions.3
May support heart health
Intermittent fasting may help support your heart health by improving risk factors associated with heart conditions.
One 2020 review examined the current literature regarding the potential cardiovascular benefits of intermittent fasting and found that intermittent fasting may positively impact multiple cardiovascular risk factors including obesity, hypertension, high cholesterol levels, and diabetes.4
Helps with weight loss
Intermittent fasting has gained popularity as a weight loss tool and studies have shown that IF may indeed help you shed some unwanted pounds.
IF leads to a reduced intake of calories and also may provide your metabolism with a boost. Additionally, IF can help increase the release of norepinephrine, a fat-burning hormone that can promote further weight loss.5
One 2017 study published in JAMA Internal Medicine showed that alternate-day fasting can be as effective as caloric restriction for losing weight. However, unlike many traditional weight loss diets, fasting doesn’t require eating certain foods, or counting calories which may make it more appealing than other weight loss plans.6
Improves Gut Microbiome
Evidence suggests that fasting may benefit your gut health by increasing the number of healthy bacteria in your microbiome.
One 2021 study analyzed the effects of 1-month of intermittent fasting on the gut microbiome and found that fasting led to an increased microbiome diversity and higher levels of Lachnospiraceae.
Lachnospiraceae are a family of beneficial bacteria that have been linked to many health benefits including supporting heart health, supporting gut health, and improving mental health.7
May increase longevity
Intermittent fasting has shown to protect against many age-related diseases which may help increase longevity. A recent review found that intermittent fasting had positive effects on risk factors for aging, diabetes, autoimmunity, cardiovascular disease, neurodegeneration, and certain cancers.8
Risks associated with fasting
While fasting carries with it a host of benefits and is generally considered safe, there are some risks to take note of.
Intermittent fasting has been linked to several unpleasant side effects including weakness, dehydration, headaches, difficulty concentrating, low blood pressure, and fainting.9
Additionally, Intermittent fasting is not recommended for pregnant or lactating women, older adults, people with immunodeficiency, or those with or at risk of eating disorders.
Furthermore, intermittent fasting may pose a danger for patients with diabetes due to the increased likelihood of low blood sugar.
While IF has been linked to enhanced heart health, skipping breakfast which is often required in some forms of IF may increase your risk of heart disease. One recent study analyzed the link between skipping breakfast and heart disease and found that skipping breakfast was associated with an increased risk of dying from heart disease.10
Intermittent fasting’s rise in popularity is attributed to its many benefits. While there are some risk factors associated with IF, it’s generally considered safe for most healthy adults.
Numerous studies have shown that IF may lead to improvements in heart health, gut health, weight management, and may even protect against disease to help promote longevity.
References:
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2.Wang A, Huen SC, Luan HH, Yu S, Zhang C, Gallezot JD, Booth CJ, Medzhitov R. Cell. 2016 Sep 8;166(6):1512-1525.e12. doi: 10.1016/j.cell.2016.07.026. PMID: 27610573; PMCID: PMC5555589.
3.Collier R. CMAJ. 2013 Jun 11;185(9):E363-4. doi: 10.1503/cmaj.109-4451. Epub 2013 Apr 8. PMID: 23569168; PMCID: PMC3680567.
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7.Junhong Su, Yueying Wang, Xiaofang Zhang, Mingfu Ma, Zhenrong Xie, Qiuwei Pan, Zhongren Ma, Maikel P Peppelenbosch, The American Journal of Clinical Nutrition, Volume 113, Issue 5, May 2021, Pages 1332–1342, https://doi.org/10.1093/ajcn/nqaa388
8.Longo VD, Di Tano M, Mattson MP, Guidi N. Nat Aging. 2021 Jan;1(1):47-59. doi: 10.1038/s43587-020-00013-3. Epub 2021 Jan 14. PMID: 35310455; PMCID: PMC8932957.
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