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.
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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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.
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.
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.
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.
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):
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
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:
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:
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:
After completing a 48-hour fast, it’s essential to break it properly. Here are some tips for breaking your fast:
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.
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):
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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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.
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):
Read more: Intermittent Fasting and Running: A Winning Combination or a Terrible Mistake?
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.
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.
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.
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).
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.
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