The Many Types of Fasting
Fasting is a fairly common practice worldwide. It involves restricting calories for at least 12 hours, but can go on for multiple days or weeks.
According to an August 2016 review in the Journal of the American Academy of Nutrition and Dietetics, fasting is typically done for either religious or health reasons. A 48-hour fast is specifically a type of intermittent fasting, which means that it might be repeated each week or each month. There are four main types of intermittent fasting:
- Alternate-day fasting, in which food and drinks (containing calories) are consumed on a set day or days, followed by a day or days with food and drink restrictions. Alternate-day fasting can be complete, with no calorie intake at all, or more similar to modified fasting that involves severely restricted calorie consumption.
- Modified fasting, in which food is consumed every day but calorie consumption is restricted on two days per week.
- Time-restricted fasting, in which food can be consumed each day but only within certain hours.
- Religious fasting, which is practiced by many different groups in different ways. Examples include Buddhists, Latter-Day Saints, Seventh-Day Adventists and Muslims during Ramadan (when people only consume food and drinks before sunrise and after sunset).
A 48-hour fast would be considered a type of complete alternate-day fasting. No foods or drinks that give the body energy could be consumed during this period. However, because water has no calories, you would be able to drink as much water as you want.
Benefits of a 48-Hour Fast
- Prevent and counteract cancer
- Extend the lifespan
- Reduce oxidative stress in the body
- Help remove dead or dysfunctional cells from the body
- Reduce obesity
- Reduce hypertension
- Reduce symptoms of asthma
- Counteract rheumatoid arthritis
- Reverse metabolic syndrome
The August 2016 review in the Journal of the American Academy of Nutrition and Dietetics also discussed how alternate-day fasting can promote weight loss, improve cholesterol and triglyceride levels, and reduce inflammatory markers.
Many other types of fasting have also been associated with these benefits. Notably, alternate-day fasting is harder to follow than other fasting regimens, but doesn't provide people with many superior benefits compared to easier types of fasting, like modified fasting or other forms of calorie restriction. In fact, when different types of fasting have been compared, calorie restriction, intermittent fasting and alternate-day fasting all reduce the same amount of fat and result in the same changes to insulin resistance.
Downsides of a 48-Hour Fast
According to both the August 2016 review in the Journal of the American Academy of Nutrition and Dietetics and a July 2017 study in JAMA Internal Medicine, multiple-day fasts and alternate-day fasting are considered to be the most challenging and least rewarding of all fasting techniques. If you're trying a 2-day water fast for weight loss, you'll certainly shed some pounds — but chances are you may gain most of them back.
- Reduced kidney function
- Bad taste in the mouth
- Skin rashes
- Runny nose and other discharges from mucous membranes
- Orthostatic hypertension (low blood pressure that occurs due to changing position too quickly)
Water fasting may produce such side effects in healthy people after about 24 to 48 hours, but people with health issues may experience them even more quickly. Even fasts that are about 12 hours long can seriously affect your kidney function if you have preexisting health issues.
If you're interested in trying a 48-hour fast, you should talk to your doctor about how to do so safely. In fact, the February 2014 Cell Metabolism review recommends that people who want to perform water fasts for 24 hours or longer only do so under the direct supervision of a physician.
Alternatives to 48-Hour Fasts
If you're considering a two-day water fast for weight loss, you may want to try a different type of fasting. A 48-hour fast can help you lose weight, but this type of weight loss is usually unsustainable. You might find that your weight yo-yos before, during and after such fasts.
Reduced calorie diets that you can follow long-term are typically considered to be more sustainable and are likely to produce longer-lasting effects. According to an October 2014 study in the Translational Research Journal, calorie restriction can help you lose more weight than other types of intermittent-day fasting, including alternate-day fasting.
However, calorie restriction still has its limitations. According to Harvard Health Publishing, most women need a minimum of 1,200 calories per day, and most men need at least 1,500 calories per day. You shouldn't consume fewer calories than this unless your doctor has advised you to do so, as consuming too few calories is often associated with nutrient deficiencies. Make sure you talk to your doctor before starting a fasting regimen or reducing your calorie intake.
Often, simply increasing your activity level and eating nutritious foods can help support safe and healthy weight loss. However, calorie restriction can also be combined with changes to your diet. Altering your macronutrient ratios, such as with the low-carb, ketogenic and paleo diets, can also support weight loss. These diets work by getting you to eat more of specific macronutrients, like protein or fat, while avoiding certain types of foods, like those rich in carbohydrates.
- Harvard Health Publishing: "Calorie Counting Made Easy"
- Translational Research: "Intermittent Fasting vs Daily Calorie Restriction for Type 2 Diabetes Prevention: A Review of Human Findings"
- Mayo Clinic: "Healthy Lifestyle: Weight Loss"
- Cell Metabolism: "Fasting: Molecular Mechanisms and Clinical Applications"
- Saudi Medical Journal: "Effects of Ramadan Fasting on Moderate to Severe Chronic Kidney Disease"
- Integrative Medicine: A Clinician's Journal: "Alan Goldhamer, DC: Water Fasting—The Clinical Effectiveness of Rebooting Your Body"
- Bratislava Medical Journal: "Effects of Complete Water Fasting and Regeneration Diet on Kidney Function, Oxidative Stress and Antioxidants"
- JAMA Internal Medicine: "Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults A Randomized Clinical Trial"
- Journal of the American Academy of Nutrition and Dietetics: "Intermittent Fasting and Human Metabolic Health"