What Can and Can't I Eat When Fasting?

  • Medical Reviewer: Mahammad Juber, MD
Medically Reviewed on 8/16/2022

What is fasting?

Fasting is an ancient practice that's still widely followed in various forms. You can eat bone broth and healthy fats during a fast and eat whole grains, fruits, vegetables, and lean protein to break a fast.
Fasting is an ancient practice that's still widely followed in various forms. You can eat bone broth and healthy fats during a fast and eat whole grains, fruits, vegetables, and lean protein to break a fast.

Fasting is an ancient practice that's still widely followed in various forms. Modern methods of fasting, such as intermittent fasting, can provide significant health benefits. Although fasting typically means consuming no calories, there are some healthy fasting foods and beverages you can have while still gaining the benefits of the fast. 

Fasting is far from a new trend. People have been fasting for thousands of years for reasons such as conserving food or practicing religious rites. Some scientists think that our bodies evolved to fast as our hunter-gatherer ancestors often had to go for long periods in between meals. 

When you eat a meal, you take in calories and nutrients that your body can use for energy. Eating consistently throughout the day means that there are always calories readily available for the body to use.

When you go for a period of time without eating, such as during a fast, those available calories get used up. Without eating another meal, the body has to turn to burning fat to meet its energy needs. 

The prevailing advice has long been to eat three square meals a day. However, regular fasting can provide many health benefits, including losing weight and improving the body's response to stress

Types of fasting

There are numerous types of fasting, many of which are considered “intermittent fasting.” Intermittent fasting involves choosing a window of time during each day when you eat and a window of time when you don’t. 

There are several different windows that are used with intermittent fasting. Popular windows of time include:

  • 16:8: fast for 16 hours and eat during 8 hours of the day
  • 18:6: fast for 18 hours and eat during 6 hours of the day
  • 20:4: fast for 20 hours and eat during 4 hours of the day 
  • 23:1: fast for 23 hours and eat during only 1 hour of the day

Another method of fasting is the 5:2 method, although the numbers in this method refer to days instead of hours. With this fasting method, you normally eat five days a week. On the remaining two days, you consume a significantly reduced number of calories, typically between 500 and 600 calories each day. 

There are other methods including more extended fasting periods, such as fasting for 24 hours or longer. These methods do not necessarily provide greater benefits than intermittent fasting, and can even be dangerous. Additionally, if your goal with fasting is weight loss, extended fasts can be detrimental — your body may begin to store fat in response to starvation instead of burn it.

Benefits of fasting

Numerous studies have shown that short-term fasts such as intermittent fasting can provide significant health benefits. 

Weight loss

One major benefit of intermittent fasting is weight loss. Studies show that intermittent fasting is effective for weight loss, with one analysis showing an average loss of 7 to 11 pounds over 10 weeks.

Additionally, some animal studies show that restricting feeding times reduces the risk of obesity and conditions related to obesity.

Improved cellular response to stress 

You aren’t the only one who may be stressed when you’re hungry. During fasting periods, the cells in your body are under mild amounts of stress since there aren’t calories readily available.

While this might sound like a bad thing, mild cellular stress may actually be beneficial. Cells experiencing mild stress, like during fasting, adapt to deal with stress more effectively. If cells face more extreme stress later on, such as during an infection, they may be better equipped to adapt.

Longer lifespan 

Improved cellular stress responses may lead to longer lives. In animal studies, modest calorie restriction leads to increased survival times. Although human studies have been less conclusive, there is evidence that fasting may lead to other benefits that contribute to longevity. 

Increased autophagy 

One possible way that fasting contributes to longer lifespans is through a process called autophagy. Autophagy is sort of a housekeeping mechanism in the body. During the process, damaged cells and cellular debris are recycled and reused as energy or as building blocks for new cells and cellular components. 

Fasting, and more generally consuming fewer calories, seem to be the best way to promote autophagy. Additionally, calorie reduction (while maintaining a similar level of nutrition) doesn’t come with negative side effects.

Improved metabolism 

Often, it’s required to fast before getting bloodwork done. This is because as little as one fasting period can reduce metabolic markers like insulin and glucose. There’s some evidence that continued fasting periods can lower other metabolic markers, such as cholesterol and blood pressure, along with blood glucose levels.

Other potential benefits

There are other potential benefits of fasting that haven't been as well-researched. Some studies suggest that fasting may improve nervous system health and optimize brain function. Other studies have found that fasting may improve endurance during exercise or improve working memory. More research must be done to confirm these effects. 


The Best Diet Tips: How to Lose Weight the Healthy Way See Slideshow

What can I eat or drink during a fast?

Technically, a fast occurs when no calories are consumed over a period of hours. Breaking a fast happens when you consume anything with calories. 

During a fast you can drink plain water and other zero-calorie beverages like black coffee and tea. In fact, it's important to continue drinking water during a fast in order to stay hydrated.

Although consuming anything with calories will technically break your fast, there are some healthy fasting foods that you can have during a fast that will allow you to still reap the benefits of fasting.

Bone broth

Bone broth, which is made by simmering animal bones for long periods of time, can be a good choice if you want to have a small number of calories without eating a full meal during your fast. Bone broth also contains vitamins and nutrients that may provide some other health benefits. 

Healthy fats 

Adding some creamer to your black coffee during a fast isn’t the end of the world. One benefit of fasting is that your body enters ketosis, in which you begin to burn fat instead of stored carbohydrates. 

Consuming small amounts of healthy fats during a fast, such as heavy cream, coconut oil, or avocado, won’t kick your body out of ketosis.

Artificial sweeteners 

Although there are many zero-calorie beverages on the market, not all of them are ideal during a fast. Many of these beverages contain artificial sweeteners that can induce an insulin response. 

If your main goal while fasting is weight loss, then these beverages should be okay to consume, but be aware that they may induce an insulin response. 

Some vitamins and supplements 

Some vitamins and supplements contain additional ingredients, such as sugars and artificial sweeteners, that will break a fast. However, the number of calories in these supplements is typically low and the benefits of getting enough vitamins and minerals may outweigh the downside of breaking a fast. 

During a fast it's important to listen to your body and decide what’s best for you. It’s better to consume a small number of calories and ensure that you’re getting appropriate nutrition than to keep a strict fasting regimen that you can’t stick to. 

What should I eat to break a fast?

Another important aspect of fasting is what you eat outside of the fasting period. Although fasting reduces your overall calorie intake, it’s still important to eat a well-balanced diet if you’re using fasting to lose weight or improve your overall health. 

Staying hydrated, exercising, and eating appropriate portions of whole grains, fruits, vegetables, and protein are all important steps for maximizing the benefits of fasting. 

Should I try fasting?

Short fasting periods, such as those used in intermittent fasting methods, are generally safe. When starting a new fasting regimen, it may take a few weeks for your body to adjust. In the meantime, you may experience symptoms such as hunger or irritability.

However, you should avoid fasting if you:

Short fasting windows are typically safe, but fasting for 24 hours or longer can be dangerous and may even be counterproductive depending on your goals. Prolonged fasting can cause nutrient deficiencies and malnutrition. It can also force your body into starvation mode, which means you'll start to store fat instead of burn it. 

Be sure to consult with your physician before beginning a fasting regimen. 

Fasting comes with numerous health benefits 

Fasting, particularly intermittent fasting, seems to have numerous health benefits that can lead to weight loss, promote longevity, and  improve your overall quality of life. When fasting, make sure you are staying hydrated with plain water and zero-calorie beverages. You can also enjoy certain foods like bone broth and healthy fats. Outside of the fasting window, it’s important to maintain a balanced diet and regular exercise routine.

Medically Reviewed on 8/16/2022

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