What if you could vastly improve your health by doing nothing at all—well, more like eating nothing at all for a period of time?
Fasting—abstaining from food for a certain number of hours or even full days—is making headlines because of its potential for big benefits. New studies, along with a slew of scientists, say it might be crucial for weight loss and anti-aging in general. It may have the potential to lower your risk of cancer, Alzheimer’s and Parkinson’s disease and even treat type 2 diabetes. So, should you be adding fasting to your wellness routine? Your questions answered below.
When did fasting become a thing?
Historically, fasting has been a tenet of cultures for centuries, during religious events such as Lent, Ramadan and Yom Kippur. But with the evolution of modern life, for many people, fasting is no longer a part of their daily routines. Food scarcity isn’t a problem either—we have access to food 24/7, and most of us take advantage of that full fridge at our first pang of hunger.
This constant eating really irks fasting proponent Dr. Jason Fung, a Toronto-based nephrologist and author of The Obesity Code: Unlocking the Secrets of Weight Loss. “We worry when someone goes three hours without eating,” says Dr. Fung. “It’s ridiculous.” For years, the most common dietary recommendation was to eat three meals a day with two snacks, leaving the body very little downtime where it’s not processing food, he says.
How does fasting work?
Fasting is not the same as starvation, says Dr. Fung. It is the controlled, voluntary absence of food for a set period of time. When you don’t eat, you start to use up the sugar in your system, the glycogen breaks down in your liver and muscles and, once those are depleted, your body starts to burn fat and ketones for energy, he explains. People start to lose weight, and naturally their insulin resistance decreases and blood cholesterol and blood sugar improve.
Not eating for an extended period of time puts mild yet beneficial stress on the body. “Your cells and organs respond to that challenge by enhancing their ability to cope with stress, which can make them more resistant to aging and disease,” says Mark Mattson, a senior investigator in the Laboratory of Neurosciences at the National Institute on Aging in Baltimore and a professor of neuroscience at the Johns Hopkins School of Medicine.
Okay, so how many hours would I have to go without eating?
There are a few different types of fasting and, though some are more extreme than others, all have similar benefits. Intermittent fasting involves days of regular eating countered by days of fasting where you don’t eat at all or consume less than 600 calories a day. The popular 5:2 diet follows this philosophy. For five days of the week, you can eat normally, and for two days in a row, you eat nothing or very few calories. There’s also alternate-day fasting, where people eat and fast every other day on a regular basis.
Time-restricted feeding is a slightly more palatable approach for many people: Working with your body’s circadian rhythm, you restrict your eating timeline to a short window—ideally nine to 12 daylight hours—giving your body 12 to 16 hours sans calories.
I guess that’s doable. But is it worth it?
Type 2 diabetes is Dr. Fung’s major concern and the focus of his work as the medical director of the Intensive Dietary Management Clinic in Toronto. In his practice, he has found that intermittent fasting has big benefits for patients who are struggling with obesity and diabetes. “These are diseases of too much fat and too much sugar,” he says. “In the right context and under the right supervision, you can reverse all of these diseases.”
Dr. Fung recently published a small study in 2018 in which three middle-aged men with type 2 diabetes tried intermittent fasting. Two of the men were able to stop taking all their diabetes drugs within a month, while the third discontinued three of four medications. All subjects lost weight, especially around their waists, and reduced their fasting and average blood glucose readings. There are still large-scale peer-reviewed studies needed before this can become a standard recommendation in most medical practices, but in his clinic, Dr. Fung says he has treated thousands of patients using fasting. “We’ve seen incredible success,” he says.
Less enthusiastic is Behnaz Abedi, a dietitian in the Family Practice Health Centre and certified diabetes educator at Women’s College Hospital in Toronto, Yes, she agrees that fasting is great for weight loss, which, in turn, improves insulin resistance and blood sugar. But there’s not enough evidence to recommend fasting to treat diseases like diabetes yet, says Abedi. Besides, she argues, diabetes goes into remission; it doesn’t go away. Remember, chronic diseases like diabetes are complex, and there’s no one-size-fits-all strategy that will work for everyone. The diet and lifestyle choices have to be conducive to someone’s lifestyle, she says, or they won’t stick with it.
What are the other benefits?
Many scientists concur that fasting helps people improve their overall health, simply by virtue of the fact that they aren’t carrying around extra pounds. But, that might not even be the biggest benefit: New animal studies show that a major advantage of fasting might take place in your brain, not your belly. A major risk factor for the most common neurodegenerative disorders—Alzheimer’s disease and Parkinson’s disease—is the changes that occur in the brain during normal aging, says Mattson. Molecular garbage, such as free radical molecules, starts to accumulate in the nerve cells and cause the damage that leads to disease. Fasting boosts the ability of cells to prevent and repair free radical damage to molecules and improves the ability of the cells to remove these aggregating proteins, explains Mattson. Basically, not eating for a long period of time allows your body to clear out the junk, preventing and repairing damage to your brain in the long term. Many of Mattson’s findings are based on mice models, not humans yet.
Do we know how fasting benefits women in particular?
In one study published in the International Journal of Obesity, Mattson and a team of researchers studied a group of more than 100 overweight young women on the 5:2 fasting diet. After six months, the women lost eight to 10 percent of their initial body weight—specifically belly fat—and had improvements to their insulin sensitivity. But most importantly, they improved other health biomarkers associated with disease risk for breast cancer, diabetes, cardiovascular disease and dementia. (Read about why Sarah McLachlan started fasting after she turned 50.)
Tell me more about its anti-aging benefits.
“One of the earliest ways to slow aging in many species is through dietary restriction,” says William Mair, an associate professor of genetics and complex diseases at the Harvard T.H. Chan School of Public Health in Boston. In a study published in the journal Cell Metabolism in 2017, Mair and other researchers found that periods of fasting promoted both healthy aging and longer life in general. By restricting diet in a type of worm, the researchers were able to maintain the animal’s mitochondrial networks in a more flexible and youthful state for longer—a finding that may have huge implications for the future treatment of aging and an understanding of the biology behind it. Keep in mind that most of the long-term studies on aging and the brain have only been done on animals, not humans, says Mair.
This all sounds good to me! Anything else I need to know?
While there aren’t enough human studies on how fasting could change your body in the long term, both author Dr. Jason Fung and senior researcher Mattson agree that it won’t affect your metabolism or its efficacy. “It’s a myth that fasting puts you into ‘starvation’ mode,” says Dr. Fung. “The body does not shut down during fasting; it tends to ramp up.” So far, Dr. Fung says that they are mostly short-term studies, but there is a lot of promise. One study published in The American Journal of Clinical Nutrition found that the metabolic rate is about 10 percent higher after four days of fasting.
Interesting. Could fasting be dangerous for anyone?
Don’t try intermittent fasting without speaking to your doctor first. If you are pregnant, breastfeeding or underweight, have a history of eating disorders or have any health issues that require medication, check with a medical professional before dramatically changing your diet.
Let’s say I’m on board—How do I start?
Experts don’t suggest going from eating the average of three meals a day and snacks to a severely restricted diet. Mattson says it takes most people a month for their bodies to adapt from constantly eating. Don’t get him wrong: It’s not easy. You will be hungry—possibly really hungry and irritable. But with all of the subjects he has studied, those side effects go away within two or three weeks and the body starts to adapt.
Go slowly, agrees Dr. Fung, especially if you’re older. If you have a health condition, you will need to work with your doctor to manage how to take your medications during the fasting period, especially when it comes to insulin and other diabetes medications, says Dr. Fung. If you take your insulin and fast, you’re doing two things that affect your blood sugar, he explains, which could be dangerous.
If you’re not game for full days of fasting, even just aiming for 14 to 16 hours overnight (say, an early dinner to a late breakfast) is enough to start getting into those fat stores and cause some cellular response. And if you exercise while you’re in a state of fasting, you can see some amplification of the cellular benefits, says Mattson.
Next, read about the one-day detox diet.