48-Hour Fast for Weight Loss: Should You Try It?

If you’ve been looking for ways to lose weight quickly, you may have come across the idea of a 48-hour fast. This type of fast involves abstaining from all food and drink (apart from water and a few low-calorie beverages) for a period of two days. During fasting hours, you’re not allowed to eat anything, but you can still consume water, tea, coffee, and other liquids that contain very few calories.

While intermittent fasting has gained popularity in recent years, longer fasts such as the 48-hour fast are still relatively uncommon and may seem extreme. Their purported benefits may also be overshadowed by concerns about safety and potential negative effects.

So, is a 48-hour fast for weight loss something you should try? If so, what are the potential risks and benefits? How can you best prepare for and break a 48-hour fast? We’ll explore all of these questions and more in this article.

Can You Lose Weight on a 2-Day Fast?

Yes, going on a water fast for 2 days can result in weight loss (23). However, it’s not a cut-and-dry solution for shedding pounds. While you may experience a dramatic decrease in the number you see on your scale after a 48-hour fast, much of this weight will likely be water weight and not fat loss.

This is because our bodies store carbohydrates in the form of glycogen, which holds onto water molecules. When we fast or drastically reduce our carbohydrate intake, our bodies use up this stored glycogen, which results in the release of that stored water and leads to water weight loss (13).

This process is simply the first in a series of steps our bodies go through when we’re fasting. The next step is burning stored fat for energy, which is claimed to result in weight loss over time.

2 days may not be enough time for our bodies to enter this fat-burning stage; a 72-hour fast may be more effective for this purpose, but it is difficult to say for certain and different individuals may have different experiences.

That being said, committing to a 48-hour fast once a week for a few months may lead to significant weight loss over time. This is because the fewer calories you consume overall, the more likely your body is to turn to fat stores for energy. 

By engaging in regular 48-hour fasts and not compensating by eating more before or after the fast, you’re effectively reducing your calorie intake and increasing your potential for weight loss.

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What Happens to Your Body After 48 Hours of Fasting?

A complex interplay of changing hormone levels, metabolic shifts, and possible cellular rejuvenation occurs within your body during a 48-hour fast (10) (19).

Factors such as age, sex, current metabolic health, and prior dietary habits can influence how your body responds to extended periods of fasting. However, there are a few general changes that tend to occur in most individuals after 48 hours without food.

Insulin Levels Drop

When you start a fast, the first noticeable change in your body is the drop in insulin levels (19). Insulin is a hormone that is responsible for managing blood sugar levels by promoting the entry of glucose into cells to be burned for energy or stored as glycogen in the liver and muscles (20).

The reason for the drop in insulin levels is simple – without food intake, there’s no surge of blood glucose due to digesting and absorbing a meal, so less insulin needs to be produced.

Glycogen Is Depleted

During a fasting state, insulin secretion decreases, which causes the body to switch from using glucose from food as its primary fuel source to tapping into glycogen stores (19). This process may take 6-12 hours, depending on prior food intake and activity levels.

For example, someone who has been eating a high-carbohydrate diet and leading a sedentary lifestyle may have larger glycogen stores to deplete, whereas someone on a low-carb diet or who exercises regularly may deplete their glycogen stores faster.

After 48 hours, glycogen stores are usually significantly depleted.

You Go into Ketosis

Once the glycogen stores are depleted, often by the end of the first day, your body transitions into a state called ketosis.

During ketosis, the liver starts to break down fat into ketones, which serve as an alternative energy source (10). Some find this metabolic shift to be helpful for weight loss, as the body starts to rely heavily on stored fat for fuel.

Ketones provide energy and also help maintain muscle mass by sparing protein breakdown. However, without any protein intake, some muscle protein breakdown is inevitable. 

Autophagy Begins

On a cellular level, fasting is believed to upregulate a process known as autophagy, where cells start to clean out damaged components and regenerate. Essentially, this is your body’s way of performing a “deep clean”, recycling old or dysfunctional cell machinery. 

This mechanism may be particularly beneficial for (1):

• Reducing inflammation – many chronic diseases are linked to inflammation and autophagy helps reduce it (3).
• Promoting longevity – autophagy has been linked to increased lifespan in animal studies (2).
• Enhancing cognitive function – research in mice suggests autophagy may be necessary for memory formation and may be important for brain health (4).

Research into when and by how much you increase autophagy during a fast is still ongoing, but effects have been seen with 17-19 hours of daily fasting for 30 days (22). 

Read more: Green Tea Intermittent Fasting: Benefits and Side Effects

How Much Weight Can You Lose in 48 Hours of Fasting?

You may lose 1-2 pounds during a 48-hour fast, but this is mostly water weight and glycogen stores. However, as mentioned earlier, the potential benefits of fasting go far beyond just the number on the scale. 

By potentially burning stored fat, promoting cellular rejuvenation, and initiating metabolic changes, a 48-hour fast may support sustainable weight loss over time if you also create an overall calorie deficit by eating fewer calories than you burn in the long term (5) (14) (18).

To increase the effectiveness of your 48-hour fast for weight loss, you should consider:

Working Your Way up to Longer Fasts

If you’re new to fasting, jumping straight into a 48-hour fast may not be sustainable for you. Instead, you should start with shorter fasting periods, such as 16:8 (fasting for 16 hours and eating within an 8-hour window) or alternate-day fasting before you attempt a full 48 hours. It’s also important to talk to your healthcare provider before you start any type of fasting regimen. 

Why it’s important:

• Starting slowly allows the body to adapt to the changes gradually, which makes it easier to stick to a fasting routine.
• It may prevent potential side effects such as headaches, dizziness, and fatigue that can occur from jumping into a longer fast too quickly.
• It may be easier to maintain as a long-term lifestyle habit.

Knowing Your Fasting Beverages

During a fast, it’s essential to stay hydrated, but which beverages are allowed and which should you avoid? Here are some common fasting beverages and their effects on your body:

• Water – the best choice for staying hydrated without breaking your fast.
• Black coffee – acceptable in moderation, as long as it’s unsweetened.
• Tea (green, black, herbal) – most teas are acceptable during a fast, but you should avoid adding any sweeteners or milk.
• Bone broth – can be consumed during a fast as it contains minimal calories and may provide some benefits. However, make sure to check the ingredients for added sugars or oils that may disrupt your fast.
• Diet soda – they are calorie-free and most artificial sweeteners don’t trigger an insulin response, but some people still choose to avoid them during a fast.

Breaking Your Fast the Right Way

After completing a 48-hour fast, it’s essential to break it properly. Here are some tips for breaking your fast:

• Start with small portions and slowly increase the amount of food over the course of a few hours.
• Stick to easy-to-digest foods to avoid potential digestive discomfort.
• Don’t overeat – listen to your body’s signals and stop when you feel satisfied.
• Drink plenty of water and stay hydrated to avoid dehydration.
• Consider incorporating probiotic-rich foods, such as fermented vegetables or yogurt, to support gut health (11) after a fast.

Eating Nutrient-Dense Foods During Feeding Windows

Fasting alone is not a magic solution for weight loss. What you eat during your eating windows plays a more significant role in achieving sustainable weight loss results.

Rather than binging on ultra-processed foods that are high in added sugar and salt and/or unhealthy fats after a fast, you should focus on consuming nutrient-dense, whole foods that support your overall health (6). This means whole grains, lean proteins, fruits and vegetables, legumes, nuts, seeds, and healthy fats. A healthy diet helps with weight loss and ensures you get essential vitamins and minerals for optimal body functioning (7).

In addition, eating a balanced diet during feeding windows can help prevent potential nutrient deficiencies that may occur from extended fasting periods.

Knowing When to Pause or Stop Fasting

Fasting can be a beneficial tool for weight loss for some people (21), but it’s important to listen to your body and know when to pause or stop fasting. Signs that you may need to take a break from fasting include (15):

• Persistent headaches
• Extreme fatigue
• Dizziness or lightheadedness
• Feeling excessively hungry during feeding windows
• Difficulty concentrating or completing daily tasks
• Any other unusual or concerning symptoms such as polyuria 

It’s important to prioritize your health and well-being over pushing through a fast. Taking breaks, adjusting your fasting routine, or consulting a healthcare professional can help ensure that you are practicing safe and healthy fasting habits.

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Is 48 Hours Enough for Autophagy?

The exact timing of when autophagy starts and its duration is still being studied, but one study saw effects with daily 17-19 hour fasts for 30 days. However, it is unclear at what point autophagy may increase during a single fast (22). 

Furthermore, there may be differences between individuals. There is still a lot we don’t know about autophagy and its relationship to fasting. 

The Downside of 48-Hour Fasting

On day 2 of fasting, hunger hormone ghrelin levels may start to increase, which makes it more challenging to stick to the fast (12). You may feel irritable, fatigued, and experience cravings for food.

In addition, 48-hour fasting isn’t safe for everyone. If you fall into any of the following categories, it’s best to consult a healthcare professional before you attempt a fast of any kind(17):

• Underweight – prolonged fasting may cause further weight loss and potentially lead to nutrient deficiencies.
• Pregnant or breastfeeding – fasting can have a significant impact on both maternal and fetal health, so it’s best to avoid fasts of any kind.
• History of eating disorders – fasting may trigger disordered eating behaviors (16) and should be approached cautiously under the guidance of a healthcare professional or not at all.
• Taking medications that require food – check with your doctor before fasting to ensure it won’t interfere with the effectiveness of your medication or lead to adverse effects.
• Undergoing medical treatment or have a chronic health condition – fasting may not be appropriate for individuals with certain medical conditions, so it’s important to consult your doctor beforehand.

Read more: Intermittent Fasting and Running: A Winning Combination or a Terrible Mistake?

FAQs

• How much weight can I lose if I fast for 2 days a week?

You may lose approximately 4-8 pounds per month if you fast for two non-consecutive days every week, which is in line with the most often recommended pace of weight loss of 1-2 pounds per week. However, this may vary depending on factors such as your starting weight, diet and exercise habits, and overall health.

• How effective is a 2-day fast?

A 2-day fast may be effective for weight loss, insulin sensitivity, brain health, and longevity when practiced consistently, but individual experiences will vary (21). It may also provide a reset for unhealthy eating habits and promote mindful eating. 

However, it’s not an easy feat and may not be suitable for everyone. It’s important to consult a healthcare professional before you attempt an extended fast.

• Will fasting for 2 days a week help me lose weight?

When it’s practiced safely, fasting for 2 days a week can be an effective tool for weight loss for some people. It allows for a calorie deficit without the need to restrict food intake every day, which makes it more sustainable for some individuals. 

However, you must also focus on nutrient-dense foods during feeding windows and maintain a healthy overall lifestyle to see lasting weight loss results (24). Overall, consistency is key for successful weight loss with fasting.

• What happens to your body on day 2 of fasting?

On day 2 of fasting, the hunger hormone ghrelin is higher than ever. You’ll likely experience hunger pangs and may feel weak or tired as your body is adapting to the lack of food intake.

Your body may also start to enter a state of ketosis, where it burns stored fat for energy instead of glucose from carbohydrates (19). You may also experience increased autophagy, which is the process of your body breaking down and recycling damaged cells (22).

The Bottom Line

A 48-hour fast may result in short-term weight loss, but its possible long-term effects on overall health may be even more significant. 

By promoting autophagy and helping to create an overall calorie deficit, a 48-hour fast can help support sustainable weight loss and may improve overall well-being. 

However, it’s essential to approach fasting safely by working your way up to longer fasts, knowing what beverages are allowed, properly breaking a fast, and understanding when to pause or stop fasting. 

With these considerations in mind, incorporating a 48-hour fast into your routine may be a beneficial tool for achieving long-term weight loss and improving overall health. You should always talk to your healthcare provider before you attempt any type of fast or fasting regimen. Fasting is not safe or appropriate for everyone.