Is Fasting Good For You?

Is Fasting Good For You?


Let’s take a few minutes to talk about fasting. Science has long since established there is a relationship between diet and health, and in the 21st century we’re trying to figure out exactly what those relationships are.


Fasting has been utilized by religious and spiritual groups for purification for hundreds, if not thousands of years. More recently, it has gained traction as a way to manage dietary intake for the purposes of weight loss and/or detoxifying the body. It may have additional benefits, but those are the two you’ve probably heard about most often.

Fasting is defined as willingly abstaining from all or some kinds of food and/or drink. The amount of time can vary depending on the parameters set by the individual. It can be for 24 hours or several days; it may be intermittent or periodic; it may also be limited to certain hours of the day such as daylight during the Islamic holiday of Ramadan. Additionally, you may choose to only fast for food but not drink, or certain types of food.

Fasting and Weight Loss

Before we go any further, I want to briefly talk about fasting as a weight loss tool. Studies have repeatedly shown that long term fasting is not a healthy way to lose weight or sustain weight loss over time. For various reasons, popular culture continues to recycle fasting “fad diets” as a way to lose weight and the science is not there to back it up. If you stop eating calories, you will certainly lose weight. However, sustained fasting can be dangerous to your health.

Fasting for a day or two is unlikely to be dangerous for most adults. High-risk people should consult a doctor before trying a fast. This includes the elderly, anyone with a chronic disease, pregnant women, and children.

The risks associated with sustained fasting, that is fasting for 3 days or longer, includes: muscle wasting, muscle aches, fatigue, dizziness, weakness and low blood sugar. You can develop anemia, a weakened immune system, liver, kidney and heart problems. It can result in vitamin and mineral deficiencies as well as dehydration. It is unhealthy and it can kill you, so do not fast for long periods of time.

Another problem with fasting as a weight loss tool is it distracts people from the essential components of healthy living: eating healthier, drinking more water, exercising and getting a healthy amount of sleep.

How does fasting work?

Next I’m going to briefly touch on how fasting works. When you eat food, your body releases many hormones, including insulin, to help digest and absorb the food. Once absorbed, the sugar gets utilized for energy, the fat is mostly stored, and the protein mostly get’s used for synthesis of hormones and enzymes, including skeletal muscle. We’ll call this the “fed” state.

When you stop eating, your body slowly stops releasing insulin and begins to increase a hormone called glucagon. The job of glucagon is to increase the amount of sugar available in circulation for your body to use. It does by recruiting stored sugar called glycogen, which will eventually run out. After 6-8 hours, your body runs out of glycogen and begins recruiting fat, and to a lesser extent protein, to produce energy. This is called the “fasting state”, and this is where you want to be if you’re fasting. You may have heard of the ketogenic diet or ketosis; this is essentially the same metabolic state.

If you go for days without eating, you can enter starvation mode. This is a difficult place to get to in modern society and it’s unlikely you will achieve this state; so I won’t mention it again. And this very brief explanation doesn’t even scratch the surface of how it all works, so if you want to know more I’d encourage you to look it up.


First, let’s discuss the concept of detoxing your body as it is probably what many people are most curious about.

Let me be clear, there is no scientific evidence that fasting will remove any harmful toxins from your body. There may be dozens of books and magazine articles on the subject, and all the different ways to approach it. However, there are no scientific publications of randomized clinical trials demonstrating that fasting can “remove toxins” from the body. There are probably plenty of medical doctors and other educated folks who believe that fasting works, but there is no current scientific evidence to back it up.

As far as I’m concerned, if your liver and kidneys work correctly, as they do in most people, there is no need to ‘detox’ or ‘cleanse’. Our body’s are perfectly capable of getting rid of any harmful toxins as long as they function properly.


Other potential benefits

There appears to be other potential benefits of fasting. In the last decade, a lot of animal research has pointed towards potential benefits of fasting in humans. The following is a list of the results of some of that animal research. Keep in mind that just because it shows promise in mice does not mean it will prove effective or beneficial in humans.

Research in animal models showed that intermittent fasting may be as effective as long-term calorie restriction in extending lifespan and improving health.

Mice forced to fast every other day, while eating twice the normal amount of food on non-fasting days, had better insulin control, resistance to nerve cell injury, and other health indicators than mice fed calorie-restricted diets.

Animal research has shown that fasting several days a week also prolongs life and prevents the development of diabetes, heart disease and certain types of cancer

More recently, researchers found that periodic fasting reduced levels of insulin growth factor-1 which helped “reset” the immune system,  kick-starting stem cells to begin reproducing white blood cells or infection fighting cells. These researchers are now beginning to investigate this on human subjects.

Here are some studies in humans.

One clinical study, published in 2007, showing a rapid, significant alleviation of asthma symptoms and various signs of inflammation in nine overweight asthmatics who near-fasted every other day for two months.

In 2008, researchers indicated that modified alternate daily fasting regimens alter fat tissue physiology (ie, body fat distribution, adipocyte triglyceride metabolism, and adipokine levels) in a way that may protect against the development of atherosclerosis and coronary heart disease.

Similar studies have demonstrated a reduction in heart rate, blood pressure, total cholesterol, and triglyceride levels after 4 to 12 weeks of true alternate daily fasting.

In 2010, researchers found fasting also ramps up autophagy, a kind of garbage-disposal system in cells that gets rid of debris and damaged cells. Increased autophagy has been associated with a reduced risk of alzheimer’s and parkinson's disease.

A 2007 study suggests that prolonged intermittent fasting has is associated with a reduction in some inflammatory markers; namely interleukin-6, c-reactive protein and homocysteine.

A 2011 study suggests that routine periodic fasting may protect against the development of diabetes in at-risk individuals. The researchers believe this occurs via increased metabolism of LDL cholesterol during fasting.

Research has also shown fasting induced release of human growth hormone; a hormone known to stimulate growth, cell reproduction and regeneration.

Finally, fasting may have immune boosting potential as demonstrated in mice, but more research is needed. Although it likely rests the digestive tract and system; I could not find any evidence identifying any direct benefits to your gastrointestinal tract from fasting. It may also have psychological benefits; but again I could not find any specific studies.

Medical Reasons for Fasting

There are a couple medical reasons to fast; namely before certain blood tests or before surgery. If you have more questions, you need to consult a physician.

Dangers of Fasting

I’ve mentioned some of the dangers of fasting. The elderly, pregnant women, children and folks with chronic disease should not fast without consulting their doctor. It can cause various symptoms, organ damage, vitamin and mineral deficiencies and ultimately death. I feel obligated to point out there are some studies that have shown negative effects from fasting.

A 2011 Brazilian study in rats suggests that long-term intermittent fasting increases blood glucose and tissue levels of oxidizing compounds that could damage cells.

In a 2010 study, periodically fasting rats mysteriously developed stiff heart tissue, which in turn impeded the organ's ability to pump blood.

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