Over the past several years, taking regularly scheduled breaks from eating — in other words, intermittent fasting — has become something of a phenomenon. But does intermittent fasting really live up to the hype? 

Is fasting really good for your health, or is it an unhealthy option in the long term?

In this article, we’ll explore the possible health benefits and risks of intermittent fasting to help you decide if intermittent fasting might be part of your health routine.

If you’re new to intermittent fasting, check out our guide on intermittent fasting for beginners and see which of the methods we share might suit you. If you need a little more help deciding your best approach, try our Simple quiz.

Why does intermittent fasting benefit your health?

We know there are many health benefits of intermittent fasting.[1] (More on this in a moment.) 

Yet, it can sometimes be hard to tell whether they are due to:

• losing weight, which occurs for many people when intermittent fasting;[2]
• more awareness of physical hunger and fullness cues;
• making wiser and more mindful eating and nutrition choices; 
• eating fewer overall calories, which has been linked to longevity;[3]
• making other lifestyle improvements, such as getting more exercise along with fasting; or
• going through the process of fasting itself — for instance, the shifts in metabolic and cellular processes that occur after several hours without food.[4]

Let’s briefly look at that last item.

What happens when you fast?

When you go without eating for around 10 to 14 hours or longer, your body goes through some changes.[5]

Pro tip: Use the fasting timer in the Simple app to see changes in your body status. Plus, our app is full of resources, recipes, insights, and support to help you reach your goals. Take our Simple quiz to get started!

First, your body starts using up stored energy in your liver and breaks down fat into free fatty acids (FFAs) in fat cells.

These FFAs then go to your liver and get turned into substances called ketone bodies, like acetoacetate and β-hydroxybutyrate (β-HB).[6] 

These are like alternative sources of energy for your body, and they help your body keep going even if you haven’t had food for a while. Researchers think that periodically circulating ketones might have health benefits.[7,8,9]   

The FFAs also activate certain cellular messengers that have effects throughout your body. Fasting also encourages your body to make more mitochondria (the energy powerhouses of cells) and makes them work a bit differently.[10,11,12]

All of these — and more — are some reasons why fasting might benefit health.

While this question may be important for scientists to figure out, “regular people” who just want to feel and function a little better can simply enjoy these benefits as they emerge. 

So, let’s look at what many people can expect to get healthwise from intermittent fasting.

What are the health benefits of intermittent fasting?

Let’s go head to toe! Intermittent fasting has been shown to improve:

• brain and cognitive health
• metabolic flexibility
• blood sugar control and insulin sensitivity
• cardiovascular health
• the gut microbiome
• sleep and circadian rhythm
• overall cellular cleanup and waste elimination

If fasting is combined with eating fewer calories overall, people lose weight, which is linked to many health improvements. 

Let’s look at each of these a little more closely.

Brain and cognitive health

Intermittent fasting appears to improve brain function in both the short and long term.[13,14] 

Thanks to the effect of certain hormones called catecholamines, many people say they feel more alert and focused while fasting. (This isn’t true for everyone, and other people report the opposite of “brain fog.”)

In the long term, fasting may lower the risk of neurodegeneration (the breakdown of our brain and nervous system tissues) and neuroinflammation (the inflammation of those tissues), both of which are linked to diseases like Alzheimer’s, Parkinson’s, and age-related dementia.[5,15,16,17] 

Even more exciting, some studies have shown that mild cognitive impairment can potentially be slowed with calorie restriction and fasting.[5,18,19] Researchers are also exploring whether intermittent fasting might be part of a treatment plan for traumatic brain injury (TBI).[7] .While we need more research in this area, initial results look promising!

Better blood sugar control and insulin sensitivity

If your doctor has ever asked you to do a fasting blood test, it’s because even a single fasting interval (usually overnight) can reduce insulin and glucose.

This is because when we eat foods with carbohydrates, our pancreas releases insulin to help our body store blood sugar (glucose) in our cells. 

When this is working well, we stay healthy and have readily available fuel and energy when we need it. When it’s not, we might have energy spikes and crashes or consistently high insulin that our cells eventually “tune out” (aka insulin resistance).

By creating periods of several hours where neither high blood sugar nor insulin is circulating, intermittent fasting helps us manage our blood sugar and improve our insulin sensitivity (i.e., our body’s ability to effectively use insulin to do its job).[20,21] 

This may not only help lower your risk of type 2 diabetes, but also lower your risk of many other chronic diseases, such as cardiovascular diseases and cancer.[22,23]

Cardiovascular health

Intermittent fasting may improve markers of cardiovascular health[5,20,21,24], such as:

• lower LDL cholesterol (aka “bad” cholesterol)
• lower triglycerides
• lower blood pressure
• lower homocysteine levels

Improved gut microbiome

The gut microbiome is the collection of friendly bacteria, fungi, and viruses that live in our gastrointestinal tract. These organisms are important for our health. 

For instance, people who have a lot of body fat often have different types of gut microorganisms than people who are lean, as well as less diversity in those microorganisms. Researchers think that the gut microbiota in people with more body fat might be better at getting extra energy from the food we eat, which can lead to weight gain.[25]

Obesity can also change the gut microbiota in a way that makes our gut more permeable, meaning things can pass through it more easily. This can lead to inflammation, which is a big problem in obesity.[26]

However, intermittent fasting may help change our gut microbiota in a good way, which could be good for our health as well as help us lose weight (or manage our weight).[25,27,28,29] This is especially true if we combine intermittent fasting with a high-fiber diet. However, we need more research to confirm this.

Sleep and circadian rhythm

Our bodies have a built-in clock, known as the circadian rhythm, that tells us when to do different things. For example, it tells us when to be active during the day and when to rest at night. 

This clock is linked to many processes in our body, like hormones, movement, sleep, and overall metabolism.

Some types of fasting might help optimize how our body clock functions.[30] 

Fasting schedules that involve eating during the day — and possibly putting most of our eating earlier, such as before late afternoon — while fasting in the evening and overnight might help our body’s clock work better, improving our overall health and how our body handles energy.

Additionally, eating at night (especially large meals) can lead to indigestion and poor sleep. Many studies have shown that when we eat late at night, we tend to sleep less and not as well.[31,32] 

Poor sleep contributes to many chronic health problems, such as diabetes, heart problems, mood disorders, and weight gain.[33]

However, by setting limits on our night-time eating (for instance, having the last meal of the day at 6 PM), intermittent fasting may help support both better sleep and the metabolic benefits of good rest. 

Overall cellular cleanup and waste elimination

Fasting may increase autophagy, a process where your cells clean out old and damaged parts. It may also increase apoptosis, programmed cell death where the cells who aren’t stepping up to the plate anymore decide to take themselves out of the game.[34,35]

It’s worth noting, however, that more research is required in this area to further understand and validate whether intermittent fasting has a key role to play in autophagy and health benefits, particularly in humans.

Longevity

Evidence from so-called “Blue Zones,” areas of the world where people live longer — and healthier — than average, suggests that eating just a little less long term might be good for us. In these regions, people either practice “eating to 80% full” or have regular fast days.[36]

The good news for those of us who enjoy food is that we needn’t eat less at every single meal. Rather, periodic intermittent fasting or fasting-mimicking diets — which means eating less at certain times and eating normally at other times — might just do the trick.[37,38]

Want to learn more about fasting-mimicking diets and how they match up with intermittent fasting? Check out our article on how intermittent fasting works with other diets. 

Health risks of fasting

While intermittent fasting in general is safe enough for most adults to try, some people should not fast.

Avoid fasting if you:

• are pregnant or breastfeeding
• have a health condition that increases frailty (e.g., undergoing chemotherapy, osteoporosis, etc.)
• are younger than 18 years of age, or are 80 years old or more
• need to take medications or have medical treatments that require you to eat
• have (or are at risk of having) an eating disorder or have a history of one
• have been told by your doctor not to fast

Remember that intermittent fasting works best when it’s intermittent — in other words, when it’s a short-term change to your body’s routine.