48-Hour Fast: Is It Healthy? Benefits and Risks Explained

Intermittent fasting is a meal timing schedule that cycles between fasting and eating windows. This type of eating schedule has become popular due to its potential benefits, including weight loss and reduced inflammation (18).

Of all the intermittent fasting schedules that are available, the 48-hour fast is the longest. If you have been intermittent fasting for a while and would like to change things up or are new to this and think that the 48-hour fast may be the best option for you, then you’ve come to the right place.

Read on to learn more about the 48-hour fast benefits and potential side effects, what breaks a fast, what 48-hour fasting results might look like, and much more.

What Is A 48-Hour Fast?

As the name suggests, a 48-hour fast is an intermittent fasting schedule that involves forgoing food for 48 consecutive hours. However, this does not mean that you will not ingest anything at all.

Anyone who takes part in such a fast is still allowed zero-calorie drinks such as water, unsweetened black coffee, and unsweetened tea without milk during these two days. Water is particularly important as it prevents dehydration, which is a huge risk in longer fasting periods such as this (17).

Does Fasting for 48 Hours Do Anything?

This eating plan has both potential benefits and downsides.

Potential Benefits of a 48-Hour Fast

May reduce inflammation 

Temporary inflammation is actually no bad thing. Your body uses this process as a means of combating infection and to stimulate tissue repair and regeneration.

However, if inflammation is chronic, this can be a problem. Chronic inflammation has been linked to several diseases such as cardiovascular disease, autoimmune conditions, type 2 diabetes, neurodegenerative diseases, and some cancers (9).

Fortunately, intermittent fasting may help reduce inflammation (27).

May improve blood sugar levels and insulin sensitivity 

When you deprive your body of food, particularly carbs, the amount of glucose in the body is automatically reduced.

It’s important to remember that the body turns carbs into glucose to use as energy. The more glucose there is in the body, the more insulin the pancreas will produce. Without any carbs entering the body, the already present glucose will be used up for energy and once that’s gone, there is no need for the pancreas to keep pumping in insulin.

Research has found that both short and prolonged fasts can help decrease insulin and fasting blood sugar levels in the body – both factors are potentially beneficial to persons at risk for type 2 diabetes (4, 6). However, if you are on medication to lower your blood sugar, you should speak to your doctor before you start any fasting regimen. 

May help with weight loss 

While research on 48-hour fasts and weight loss is not readily available, intermittent fasting has been found to help with weight loss. 

Fasting in general can help reduce your overall caloric intake, which is essential for body weight and fat loss (19, 5).

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48-Hour Fast Side Effects

Despite the potential benefits, going without food for a prolonged period is not an easy task. Some side effects you may experience during this fast include (13):

1. Fatigue
2. Dizziness
3. Irritability
4. Nausea
5. Headaches
6. Fainting
7. Insomnia or interrupted sleep 
8. Hunger pangs and digestive issues

Is It Healthy to Fast for 2 Days?

As demonstrated above, a 48-hour fast has benefits and side effects. However, it should be noted that while some people will be okay on a prolonged fast, others will absolutely not be. 

Fasting for 2 days (or at all) is not healthy and is highly discouraged for the following groups of people (20, 11):

1. Children and teenagers under the age of 18
2. Women who are currently trying to conceive, are pregnant, or are breastfeeding
3. People with a history of eating disorders – fasting may trigger an eating disorder
4. Women with a history of amenorrhea – prolonged fasting or intermittent fasting for women is discouraged as it has been found to have adverse effects on the menstrual cycle (7, 2)
5. People with low blood pressure or those taking insulin for diabetes
6. Anyone who is taking heart disease or blood thinner medication and people who are taking NSAIDs (nonsteroidal anti-inflammatory drugs)

It’s always a good idea to talk to your healthcare provider before you start a fasting routine or attempt a longer fast. They can help determine whether it is safe for you and if any special considerations need to be taken.

Will A 48-Hour Fast Put Me in Ketosis?

Yes, that is most likely.

Ketosis is a metabolic state in which your body converts stored body fat into ketones before using it as a source of energy to keep you going.

The body normally converts ingested carbohydrates into glucose to use for energy. However, if the carbs and glucoses are not available, you will enter ketosis and start to burn stored fat (23).

It should be noted that you do not need to fast for 2 full days in order to reach ketosis. According to Harvard Health Publishing, your body may enter the ketosis state after just 12 hours of not eating (24), which is the duration between dinner and breakfast for most people. 

You can also enter ketosis without fasting at all. By reducing your carbohydrate intake to 20 to 50 grams of carbs per day, you can naturally enter this state in 2 days to a week – sometimes longer. This is called a ketogenic diet. 

The time it takes varies from person to person (21, 14). If your diet is quite high in carbs before you drastically reduce your intake, it may take you longer to enter this state compared to someone who gradually eats less carbohydrates (16).

Read more: The Benefits of 40 Hours Fasting: Do They Outweigh The Potential Risks?

Is a 48- or 72-Hour Fast Better?

If you are trying prolonged fasting for the first time, a 48-hour fast is definitely better than a 72-hour fast as it’s shorter and therefore, easier to complete.

Research has shown that calorie restriction for more than 48 hours has more potential disadvantages than advantages. Some of those side effects include:

1. May affect neurometabolism (3)
2. May reduce immunity  

A study review that was published in 2019 showed that longer fasts can reduce your immunity by reducing the number of white blood cells (monocytes and lymphocytes) in the blood, among other effects (26).

36- or 48-Hour Fast: Which One Should I Start with?

If you want to train your mind and body to withstand long fasting periods, it is advisable to start with 24- to 36-hour fasts rather than the full 48 hours. Once your body can comfortably manage 36 hours, you can work toward a 48-hour fast.

How Much Weight Can You Lose in a 48-Hour Fast?

Not much, particularly if this is your first time with this intermittent fasting cycle. Unfortunately, some online sources claim you can lose anything between 1 and 6 pounds during a 48-hour water fast, but this is a lie, especially if we are talking about fat. 

48-hour fasting before and after pictures posted online may convince you otherwise, but it’s important to note that the only weight that is lost during a water fast comes from water, glycogen, and a small amount of muscle mass, but not body fat.

In order to actually lose body fat with this eating cycle, you may need to make 2 days of fasting an occasional part of your routine over a period of several months.

To get the best results, you will need to combine cardio and weight training exercises with a healthy calorie deficit diet (during feeding days) and drink more water to cause more calorie burning.

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The Bottom Line

Fasting is a popular strategy for weight loss and other health goals. However, it should only be done regularly if it’s done in short bursts i.e. less than 24 hours of fasting a day.

If you want to try prolonged fasting in the hope of achieving the same or better results, it’s important to understand that a 48-hour fast, while it has its benefits, also comes with some risks. If you are new to fasting, intermittent fasting or time-restricted eating may be a better strategy for you than prolonged fasting. 

Longer fasts are generally done under medical supervision, so they are definitely not beginner-friendly. However, if you are used to fasting, you should make sure to stay hydrated and rest as much as possible during these two days.