Why Fasting Causes Autophagy — and What's the Deal With That, Anyway?

In recent years, the buzz around fasting — and especially intermittent fasting — has grown louder. While weight loss is the main draw for many, there's another benefit of fasting that's piqued a lot of interest.

Researchers have found that when your body is in a fasted state, it undergoes a process of cellular housekeeping called autophagy, which they've linked to disease prevention and longevity.

Here, we'll break down the science behind fasting and autophagy to give you a clearer picture on what it really means for your health.

Autophagy (pronounced ah-TAH-fah-gee) is an opportunity for your cells to take out the garbage, says Cynthia Thurlow, NP, nurse practitioner and functional nutritionist who specializes in intermittent fasting. It's a natural process of cellular repair and cleaning.

"Autophagy gives your body a reboot and allows your body to function more effectively," Thurlow tells LIVESTRONG.com.

Think of your cells like an oven. Over time and as you age, your cells collect damaged proteins, fragmented pieces of white blood cells or enzymes and other metabolites that no longer work well or efficiently — much like your oven collects grease and grime from your meals. If this "waste" isn't removed, your cells don't work as well or as efficiently.

Autophagy is like your cells' self-cleaning function.

"It slouches off this junk, this inflammatory debris, that it should be sloughing off but has kept around," says Myles Spar, MD, MPH, a board-certified physician and author of ‌Optimal Men's Health‌.

Cells then recycle that material for fuel and building blocks for new cellular parts, according to the Cleveland Clinic.

So, our cells have a decluttering routine. What's the big deal?

Autophagy is necessary for our cells to survive — the process provides materials for cell parts, removes nonfunctional cell parts and breaks down pathogens in cells, according to the Cleveland Clinic. Plus, the process may play a role in preventing disease, per the Cleveland Clinic.

However, research on the health benefits of autophagy is still in early stages. Most studies have been conducted in animal cells, and it's not clear if the findings translate directly to humans, according to the Cleveland Clinic.

Plus, there's no accurate way to measure autophagy in humans, according to an August 2017 review in the ‌International Journal of Molecular Sciences‌. And, according to the authors of a January 2015 study in ‌The Journal of Clinical Investigation (JCI)‌, it's not always clear if the results are tied directly to autophagy or to something else.

Still, researchers have identified some promising potential benefits of autophagy:

By removing accumulated, damaged cellular material, autophagy may lead to a decline in age-related diseases and increased longevity. According to the ‌JCI‌ study, autophagy contributed to longer lifespans in cells, animals and humans.

A May 2018 review in ‌Biomedicine & Pharmacotherapy‌ found that autophagy can suppress cancer. Indeed, when genes that regulate autophagy are disrupted, there are higher rates of cancer.

Thurlow says that's because autophagy discards diseased cells that could potentially become cancerous. However, the authors note that there are also times when autophagy protects cancerous cells and helps them grow.

Another paper, published November 2018 in ‌Clinics‌, found that autophagy induced by fasting may make cancer treatment more effective.

In addition to getting rid of unwanted cellular material, autophagy may also remove bacteria, viruses and other pathogens that can cause infections, according to a June 2015 study in the ‌Journal of Experimental Medicine‌. It also helps keep the body's inflammatory response in check.

The authors of the above 2015 study also found that autophagy plays a role in protecting against neurodegenerative disease by removing proteins associated with conditions like Alzheimer's, Huntington's and Parkinson's disease.

According to the authors of the ‌Biomedicine & Pharmacotherapy‌ review, research in mice shows that autophagy decreases obesity and insulin resistance by removing oxidative stress and damaged mitochondria.

A March 2013 study of women in the ‌British Journal of Nutrition‌ found that intermittent fasting led to greater insulin sensitivity (which lowers blood sugar by allowing the body's cells to use blood sugar more effectively).

"We know higher insulin levels are associated with metabolic conditions like diabetes, vascular disease and higher levels of inflammation," Thurlow says, so insulin sensitivity is a good thing.

Autophagy is one way your body responds and adapts to stress. According to a November 2018 study in ‌Ageing Research Reviews‌, fasting is one of the most potent ways to stimulate autophagy in the body.

"In a fed state, the cells don't have to be efficient, so they don't clean up as much," Dr. Spar says. "When you strain the system in a good way, like with fasting, suddenly the cell senses that it doesn't have a ton of nutrients and that it shouldn't be wasting what it does have."

But autophagy needs to cycle on and off, Thurlow says. Too little or too much cellular cleaning can cause problems.

"Fasting is a super efficient way to tap into autophagy, and it doesn't require any special products or technology."

For the average American, though, Thurlow says we don't give our bodies a chance to fast because we eat frequently and often, which can overtax our systems. As a results, you bypass opportunities to tap into this beneficial process.

In particular, intermittent fasting — when you restrict what you eat to certain hours of the day or to specific days of the week — is one way to allow your body to regularly cycle through periods of eating and fasting. This triggers a hormonal response in the body that jumpstarts the cell's stress response, immune defense and mitochondrial function (the cell's energy powerhouse) in addition to its self-cleaning cycle, according to a December 2019 paper in ‌The New England Journal of Medicine (NEJM)‌.

"Fasting is a super efficient way to tap into autophagy, and it doesn't require any special products or technology," Thurlow says.

The trick is that your body needs to flip the metabolic switch from burning glucose (aka sugar) for fuel to using fatty acids and ketone bodies for energy, according to the authors of the ‌NEJM‌ paper. This can take between 10 to 14 hours of fasting.

Both Dr. Spar and Thurlow say there are many benefits to intermittent fasting aside from autophagy. And it's pretty simple to follow. They recommend fasting for anywhere between 16 to 18 hours a day to reap the benefits. However, fasting for more than 24 hours can start to overstrain the body, Dr. Spar says.

"Skip breakfast. Have lunch and dinner, and you can have a social life," Dr. Spar suggests.

Thurlow says that intermittent fasting works well with any nutritional ideology too, whether it's paleo, keto or a gluten-free diet.

But you don't have to be rigid about your fasting schedule, especially if you're trying intermittent fasting for longevity and disease-prevention reasons.

"You're in this for the long run so don't stress out because stress is bad for longevity," Dr. Spar says.

Just try to be consistent. "Even if you fast twice a week, that's going to be beneficial compared to not doing it at all," Thurlow says.

Consider working with a registered dietitian to ensure that you're meeting your nutritional needs.

However, if you have diabetes or other blood sugar issues, are pregnant or breastfeeding, have underweight or a chronic disorder such as vascular, kidney or liver disease, Thurlow suggests steering clear of fasting.

Dr. Spar doesn't recommend intermittent fasting for children under 18 or if you're training for an endurance event like a marathon or triathlon. In both cases, you'll need all your energy stores, he says.