Over the last few years, fasting has become one of the most popular mainstream diet strategies.  From biohackers looking to improve brain function to dieters looking for rapid weight loss, it seems like everyone has tried fasting at least once.

With such a surge in popularity, it’s easy to forget that fasting has strong therapeutic potential and can help manage several different medical conditions. Not to mention fasting as an ancient practice that plays a central role in several religious traditions and cultures. Even Hippocrates, often referred to as “the father of modern medicine” referred to fasting as “the greatest remedy, the physician within.” 

But what is fasting, really? And how can you get all of the medical benefits of fasting? Read on to find out.

What is Fasting?

Fasting is abstaining from all food and caloric drinks for a specific period of time — ideally long enough to exhaust your body’s sugar stores so you can start burning fat. For most people, this is anywhere from 24 to 72 hours, but intermittent fasting (IF) allows you to cycle between shorter periods of fasting and eating windows. 

A standard intermittent fasting window involves a 16-hour fast, with an 8-hour eating window. But other IF cycles include one 24-hour fast per week, or fasting every other day. However you choose to fast, you might want to check with your doctor or a coach first. And remember — longer fasts aren’t necessarily better and may be dangerous.

Once you’ve chosen your fasting cycle, it’s time to experience the benefits. Here are just a few medical uses of fasting, backed by science. 

Fasting for Epilepsy

One of the first documented medical uses of fasting was for epilepsy. In fact, Hippocrates and other ancient doctors prescribed fasting for epilepsy and, until the early 1900s, fasting was still considered the primary treatment option for children with the condition.[1

It’s believed that fasting may work by directly impacting the activity of nerve cells, which in turn results in fewer epileptic seizures.[2

Interestingly enough, fasting for epilepsy actually led to the discovery of the ketogenic diet in the 1920s due to the diet’s ability to mimic fasting while still allowing for food consumption.[3]  Shortly after, anti-seizure medications came to the market and both fasting and the keto diet fell out of favor until the last decade or so. 

Fasting for Medical Weight Loss

It’s hard to talk about fasting without mentioning its weight loss potential. After all, weight loss is the primary reason most people are willing to try fasting in the first place. Fasting is an efficient way to not just lose weight, but lose fat as opposed to the muscle loss that can sometimes come with caloric restriction. It's important to note, however, that if you want to maintain muscle mass while fasting you must engage in some form of resistance training.[4]

Fasting can contribute to weight loss through several mechanisms. The first is that fasting reduces blood sugar and insulin which triggers fat burning to take place. So, fasting not only induces fat-burning in the short-term, but in the long-term as well as you continue to improve fasting blood sugar and metabolic health.[5

Fasting can also help with weight loss by inducing a calorie deficit. While calories in-calories out isn’t the only explanation for weight loss, they still play a role. Shorter eating windows can naturally reduce caloric intake and may improve metabolic function and balance blood sugar overtime, reducing cravings for high-calorie snacks.[6,7

Furthermore, fasting may produce benefits in obesity-related health issues such as high blood pressure, elevated cholesterol, elevated triglycerides, microbiome abnormalities, and appetite regulation.[8

Fasting for Diabetes

Diabetes and prediabetes are conditions characterized by elevated fasting blood sugar and insulin resistance. 

In type 2 diabetes, there are two factors contributing to high blood sugar; your pancreas is not producing enough insulin to meet your metabolic needs, and your cells have become desensitized to insulin’s signals. Insulin is the hormone responsible for shuttling glucose into your cells, therefore when insulin isn’t functioning properly blood glucose builds up resulting in hyperglycemia.[9

Research shows that after a period of fasting insulin sensitivity increases and insulin levels tend to fall. This may be in part due to the impact of calorie restriction on insulin sensitivity. Furthermore, one of the clinical markers for diabetes is increased levels of systemic inflammation. Intermittent fasting has been shown to improve various metabolic inflammatory pathways.[10]  

Research has found that long-term fasting can lead to improvements in fasting blood sugar and HbA1c, the most common marker of diabetes.[11,12

Note: Fasting can backfire if you’re already on medication for diabetes or pre-diabetes. Make sure to consult your doctor before incorporating fasting.

Fasting for Cancer

This sounds like it must be too good to be true, but there’s some promising evidence that fasting can be used alongside other treatments to help treat certain types of cancer. 

Research looking at both radiation and chemotherapy have found that these treatments produce more robust results when the patient fasts prior to treatment.[13,14]

That’s likely because cancer cells thrive on sugar. When patients fast before radiation or chemo, they’re essentially starving cancer cells of their primary fuel source, making them weaker and more susceptible to the effects of the treatment.

In addition to being used alongside radiation and chemo, fasting to starve cancer cells may also help between treatments to keep cancer from spreading or coming back.[15]

Note: While fasting may be beneficial, cancer patients also need nourishment. Make sure to work with your doctor to plan accordingly and ensure sufficient calorie intake. 

Fasting for Alzheimer’s Disease

Fasting has a profound impact on the brain, mostly due to the ketones that are produced when we fast. Ketones are powerful energy molecules produced by your liver when you restrict carbohydrates or otherwise burn through glucose and glycogen stores. 

It turns out that your brain prefers ketones as a fuel source due to their ability to provide more energy to the brain more quickly than glucose. Ketones also activate anti-inflammatory pathways while producing less oxidative stress — definitely a recipe for long-term brain health.

The aging brain is characterized by an increase in insulin resistance and a subsequent decrease in energy available to the brain. Research has found that under these conditions, the brain can still use ketones to help resolve this energy crisis and potentially reduce symptoms of neurodegenerative diseases.[16]

Fasting for TBI (Traumatic Brain Injury)

Until recently, there was very little consideration paid to the role of nutrition in traumatic brain injury (TBI) recovery.  However, as we have begun to understand more about head trauma, we have discovered that a defining characteristic of the condition is neuroinflammation and a subsequent energy crisis in the brain.[17

While the research is still in its infancy, there is evidence that ketones can help increase energy uptake in the brain post-head-trauma, while also working to lower the inflammation.[18

Fasting’s ability to induce ketosis could also make it a great complementary tool to use in the treatment and long-term recovery of concussions and traumatic brain injury.[19]

It’s important to call out the lack of randomized controlled trials available for the medical uses of fasting. Research costs money and money typically comes from sources that have a return in mind. Unfortunately, there isn’t much money to be made in not eating anything. 

Regardless, the mechanisms are present and the anecdotal evidence is mounting.  In time, we may find that one of the best treatments or supporting treatments to so many conditions is to not do anything at all…

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