Most people would agree that going hungry is a bad thing. But what if the occasional growling stomach (and accompanying symptoms like dull headaches, fatigue, weakness, irritability, and poor concentration) was simply the price of admission to the fountain of youth?
That’s what recent science on intermittent fasting and periodic fasting has started to suggest. What’s more, along with increased longevity and slower aging, preliminary research also shows that fasting could jumpstart weight loss, improve immunity, and deliver a multitude of other health benefits. No wonder it’s becoming a trend.
But while fasting certainly has some of the hallmarks of a fad diet or transient health trend, it’s not a new or completely out-there concept. Humans have been fasting for centuries for religious or spiritual reasons. And the science backing up many of the claims, even though much of it is relatively preliminary, is also solid.
Indeed, cutting way back on food does seem to trigger a number of changes in the body that help various systems function better, fight disease, and generally stay healthier, longer, according to a recent review in the New England Journal of Medicine. Scientists have actually known for quite a while that one of the most effective ways to improve longevity is calorie restriction. The less you are able to eat and still survive, the longer it seems you may live, at least according to animal studies.
The problem, of course, is that spending life in a state of near starvation doesn’t make for a very pleasant one, nor is it really sustainable. After all, who cares if you live to be 110 years old if you’re miserable and hungry all the time?
With that in mind, researchers have been trying to determine whether we can mimic the positive effects of severe calorie restriction through a more tolerable protocol — or at least gain some of the same benefits. And what they’ve found is that certain forms of fasting may indeed be the answer.
What is Fasting, Exactly?
While fasting can mean a lot of different things — even in research studies, the protocols vary widely — it typically involves going with little or no food for anywhere from around 14 hours to several days. Here, three of the most common types of fasting:
Also called time-restricted eating, this is one of the most popular ways to fast. It requires shortening your window of eating to only 6 to 8 hours a day. For obvious reasons, most people choose to set the majority of their fasting period so it falls at night, while they’re feeling satiated from an evening meal or sleeping. So, for example, one might choose to eat only between the hours of noon and 6 p.m.
Alternate-Day Fasting and the 5:2 Diet
Both are also sometimes referred to as intermittent fasting. Alternate-day fasting, as the name suggests, usually means you eat only about 500 calories every other day, and a normal 2,000 to 2,500 calorie diet otherwise.
The 5:2 diet, which has been studied by researcher Mark Mattson, Ph.D., a professor of neuroscience at Johns Hopkins University, involves eating only one moderate-sized meal (around 500 calories) twice a week on non-consecutive days, and then following a normal, balanced diet the other five days of the week.
This one was developed by researcher Valter Longo, Ph.D., director of the Longevity Institute at the University of Southern California. It’s a program where, a few times a year, you spend five days in a row eating very few calories (1,100 on day one, then 800 a day following), mostly from vegetables, nuts, and plant oils. Afterward, you go back to your normal diet. Because this type of fasting is something you do only occasionally, rather than regularly, it’s sometimes called periodic fasting.
What Happens to Your Body When You Fast
Fasting triggers a number of systemic and cellular changes in the body that research suggests may translate into lower risk of, or improved outcomes for, a number of conditions that affect health and life span, including cardiovascular disease, diabetes, obesity, metabolic syndrome, cancer, and neurodegenerative disorders such as Alzheimer’s and Parkinson’s. Here, a few of the specifics:
You Switch to a New Fuel Source
After about 8 to 12 hours without food, your body runs out of its go-to gas: glucose from food and stored glycogen. At that point, your liver starts converting fatty acids to a type of acid called ketones, which your body burns for energy instead.
Aside from being an efficient fuel source, ketones act as signaling molecules that regulate proteins and cellular pathways that play various roles in health and longevity. In the long term, regularly triggering this metabolic shift can improve several markers of health that impact longevity, including improved sensitivity to insulin and lower levels of inflammation.
Your Mitochondria Get a Break
Mitochondria are organelles within each cell that serve as energy-producing power plants. They turn carbohydrates into ATP, an organic chemical that fuels cellular functioning.
Aging occurs when mitochondria burn out over time. It’s in part a natural process of wear and tear, but there are various factors that speed things up. One of the main contributors to the acceleration of mitochondrial burnout: Loading your body with excess energy (as in, too many calories) and not engaging in physical activity that uses that energy.
Shutting off the constant influx of calories through fasting may alleviate some of that stress on mitochondria so they burn out more slowly. Fasting may also trigger production of new mitochondria and aid in the disposal of old, worn-out ones, plus prompt other changes to mitochondrial networks that keep them in a more youthful state.
Your Cells Get Better at Managing Stress
Another important way fasting may increase longevity is through cellular stress adaptation. Organs and cells respond to intermittent fasting by becoming better at dealing with harmful stressors, according to a recent review in the New England Journal of Medicine. For example, the research shows an increase in antioxidant defenses, improved DNA repair, and a down-regulation of inflammation, all of which help protect cells from aging and disease.
There’s More Energy for Health Maintenance
While consuming food provides fuel your body converts to energy, the process of digestion itself also requires an extraordinary amount of energy. When you fast, those energy demands go away. As a result, your body is able to divert more energy and resources toward repairing cells and structures, clearing away cellular and mitochondrial garbage, and generally improving cell and system functioning.
Your Microbiome and Immune Response are Bolstered
When you eat throughout the day, you’re introducing a near-constant stream of foreign proteins and bacteria to your system that have the potential to cause problems. The job of policing those outsiders largely falls to the microbes in your GI tract (aka your gut microbiome), which are the first line of defense against foodborne microscopic invaders as well as an essential component of your immune system. In other words, eating works both your digestive and immune systems hard.
On the other hand, if you go for periods where you eat very little or shorten your eating window, it reduces the burden on your gut microbes, allowing them to redirect their immune-boosting efforts elsewhere. Fasting also means there’s less food for pathogenic and opportunistic microbes to survive on, so they die and move out of your system (usually via a bowel movement) more quickly.
A study in the journal Cell Stem Cell also found that when the body switches over to ketone fuel during fasting, your immune system may be triggered to target and kill off old damaged white blood cells that can gum up the works of your immune response. Then, when you begin eating again, stem cells begin restocking your immune system with healthier white blood cells.
Ask Yourself These Questions to Determine if Fasting Right for You
While preliminary evidence is promising and many experts and laypeople alike tout the benefits of fasting, it’s not for everyone. Here’s what to consider before beginning any fasting program.
1. Have You Consulted Your Doctor?
If you want to give fasting a go, your healthcare provider can discuss potential risks unique to your situation or health. That’s especially important if you have diabetes or any other medical condition or chronic illness, or if you take medications or have poor gut function. Nutrient intake and the shift in metabolism that happens during a fasting period can impact all of these things.
2. Are You OK with Being Uncomfortable?
Some people like and do well with the strict and simple rules around fasting, especially time-restricted eating. After all, unlike some complicated diet plans, it’s pretty cut-and-dry: Eat only during this time, do not eat during that time.
However, other people find the reality of it incredibly difficult. Along with intense hunger, you may experience irritability and trouble concentrating; you may also feel weak or lightheaded, or develop a headache.
Aside from the physical symptoms, fasting also runs counter to our culture, where food is abundant, marketing tactics are hard to resist, and the three-meals-a-day way is deeply ingrained in how we socialize. For all those reasons and others, studies show people don’t like fasting or can have trouble sticking with the protocols, and so a large percentage give up.
Keep in mind, however, that research also suggests that after about a month, your body may start to adapt so that fasting feels more tolerable. You might no longer feel the same intensity of symptoms or any side effects at all.
One thing experts say may help with intermittent fasting: Gradually adopt a longer fasting window over the course of several months. For example, start by shortening your window of eating to 10 or 12 hours, adding an hour every week or two until you reach a 16- or 18-hour fasting period.
If you choose one of the other types of fasting, likewise gradually cut calories on fasting days. For example, on the 5:2 plan, start with only one day of fasting and consume 1,000 calories to start on that day. After a month, add a second fasting day. Then cut back to 750 calories during your fasting periods, and then eventually to 500.
3. Do You Actually Need to Fast?
If you eat plenty of vegetables, are physically active and at a healthy weight, manage stress, get enough sleep, and support your health with restorative herbs — in other words, if you’re already healthy and doing what you can to support your systems and cells — it’s unclear whether or how much of an additional difference fasting will make in your health and longevity. The science still has a way to go in understanding the benefit of fasting when compared to that of other good habits and behaviors.
On the flip side, if you’re not healthy, it’s not advised to use fasting as a way to offset or compensate for, say, a sedentary lifestyle or poor diet. Also, realize that fasting may leave you with less energy to be physically active, which science has unequivocally shown improves health and longevity, not to mention improves mental health and mood.
I’m not advocating against fasting, necessarily — humans have been fasting for centuries, and it can be a good thing. However, know that intermittent fasting may require rethinking your schedule and normal activities, like when and how you exercise. At a time when many people already find it difficult to fit physical activity into their busy routines, adding another impediment may not be a smart choice.
As for periodic fasting, it likewise can be difficult to take two or three days out of your life to do it. (And you may find you do need to put life on hold, since periodic fasting can be difficult to sustain while also engaging in regular work and life activities.) You may find you prefer to do something you really enjoy that’s also healthy, like kayaking or biking, rather than take time away from your usual routine.
The Bottom Line
Although fasting may be beneficial, the broader take-home message is this: Consuming calorie-dense processed food and meat products often and all day long is indeed a huge burden on your system. These foods contain high-energy, highly-reactive compounds that can lead to weight gain and increase your risk of chronic diseases. Plus, they can damage and stress your cells, accelerate mitochondrial burnout, and age you faster.
But while fasting may indeed be a simple if not quick fix, it’s just one tool in the toolbox. For example, recent research from Harvard has also pinpointed 5 other, more moderate habits that effectively and reliably increase life expectancy and reduce risk of developing diabetes, cardiovascular disease, and cancer as you age:
- Eating a healthy diet
- Exercising regularly
- Maintaining a healthy weight
- Drinking alcohol infrequently or moderately
- Not smoking
So, if you haven’t already, consider adopting the behaviors on this list, starting with increasing your consumption of low-calorie, high-nutrient vegetables and enjoying more physical activity. After that, you might try shortening your eating window to a more conservative 10 or 12 hours a day.
All of these strategies are effective, and they’re more moderate and doable ways to improve health, lose weight, relieve stress on cells and mitochondria, and ultimately slow the aging process and increase life span. Then, if you want to go beyond that and try fasting, go ahead (with your doctor’s blessing) and see how it feels.
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