No doubt that intermittent fasting is all the rage these days. The practice, which actually dates back to the biblical times, involves time-restricted eating, or eating within a specific window, and fasting within another window.
The idea is to give your body a break so that you’re not fully in digestion mode, and proponents of IF say that this pause is when a whole host of benefits begin. The practice comes in many different forms, such as abstaining from food for eight hours to going an entire day without eating—and celebs like Jennifer Aniston, Oprah, Kourtney Kardashian, are fully on board. But what are the benefits of intermittent fasting, and how long will it be until you see results? And how do you know if you’re doing it right? Parade.com talked with the experts to find out—here’s what they said.
Benefits of intermittent fasting
It may help with weight loss
Sheri Vettel, a registered dietitian nutritionist in North Carolina, says the most sought-after benefit of intermittent fasting is weight loss. “This is good news, as numerous studies have found the practice to be favorable for weight—whether it shows up on the scale or in another way—such as fat mass loss and/or decreased waist circumference,” she explains. In fact, per Vettel, intermittent fasting has been linked to loss of visceral fat, or the type of fat that pads internal organs and leads to health issues, such as heart disease
It may help you live longer
“One of the most exciting potential benefits of intermittent fasting is increased expression of SIRT-1, a gene linked to longevity,” says Vettel. She explains that while the sample size of the study that found this link was small, it’s well known that caloric restriction in animals leads to a longer lifespan. “It’s important to note that while animal studies are certainly not human studies—and therefore the results cannot be directly applied to humans—this knowledge may provide some insight into potential anti-aging effects of intermittent fasting. Research in humans has found that intermittent fasting leads to lower levels of oxidative stress and inflammation, which confers disease-fighting benefits increasing the likelihood of a long and healthy life.”
It could benefit cardiovascular health
According to Vettel, intermittent fasting may enhance heart health with reductions in total cholesterol, LDL levels, and triglyceride levels. “One study found that alternate day fasting for 60 days resulted in additional benefits as well, including lowered resting heart rate and a decrease in homocysteine—an amino acid known as a risk factor for heart disease,” she explains. Research has also linked intermittent fasting to lower blood pressure levels, with one study noting a significant drop in both systolic and diastolic blood pressure readings after a five-week time-restricted feeding intervention.
It may activate cellular stress responses
This, says Dr. Josh Axe, founder of Ancient Nutrition and author of the best-selling book KETO DIET, can result in lowered levels of oxidative stress, which helps to promote healthy aging. “Fasting seems to act on similar biological pathways as calorie restriction,” he explains. “It’s thought to positively impact expression of genes associated with healthy aging and may manipulate mitochondrial networks inside cells that can help increase lifespan.”
It may help with blood sugar regulation
Brynna Connor, MD a board-certified family physician in Texas, highlights that some studies have also shown that intermittent fasting plans can improve insulin sensitivity and blood sugar levels, meaning that their bodies can better digest and use sugar. “When the body becomes more efficient at metabolizing sugar, a person is less likely to develop diabetes,” she says. Connor notes, however, these studies have only looked at short-term health effects, and some other studies have shown mixed results. “It’s not entirely clear yet whether intermittent fasting can directly lower a person’s diabetes risk in the long run.”
It could provide brain benefits
Taking a break from eating may also benefit your cognition. “Intermittent fasting may also help the brain age in a healthy manner by encouraging brain cells to grow and form new connections,” says Connor. “Animals who fast are better protected against injury and have lower rates of Alzheimer’s disease and Parkinson’s disease.”
It may be cleansing
“Intermittent fasting helps with longevity and getting rid of Senescent cells or ‘zombie cells’ by cellular autophagy (a process in which your body removes damaged cells and proteins),” says Cynthia Thurlow, an intermittent fasting and nutrition expert who has delivered a TED talk on the subject.
She explains that when you fast, this autophagy process will essentially starve the zombie cells. “Why don’t you want zombie cells? These are essentially old cells that have damage to their DNA and no longer are useful in the body,” Thurlow notes. She explains that we all have these bad cells in our bodies, but we want to get rid of as many of them as we can and essentially replace them with healthier cells full of life. “Doing this will get rid of inflammation, possibly lower your cancer risk, stop the secretion of toxins by the zombie cells, and contribute to aging gracefully,” Thurlow says.
It could help with appetite regulation
Intermittent fasting, says Axe, can often help to regulate one’s appetite. “This happens because fasting can positively affecting release of ‘hunger hormones,’ including leptin and ghrelin,” he explains. “This can make you feel fuller after eating, potentially helps to decrease fat storage and increases energy expenditure.”
Intermittent fasting 16/8 benefits
The 16:8 method is a form of time-restricted eating in which people have an 8-hour window to eat, and 16 hours of fasting. Dr. Pamela Peeke, lifestyle medicine expert and chair of the Jenny Craig Science Advisory Board, explains that “the longer the fasting window (with 16 hours as the limit), the greater the benefits.”
Dr. Michael Roizen, a Cleveland Clinic doctor and author of The What to Eat When Cookbook, adds, “This way of eating changes gene function and markers of aging, stem cell repair and inflammation to all improve within four days.”
There are many different types of intermittent fasting, including the 5/2, which involves eating normally five days a week and drastically limiting calories the other two; alternate day fasting, where you fast every other day; the 20/4 method where you fasting for 20 hours per day and eat within a four-hour window; and the 24-hour method, which involves forgoing food for an entire day at a time. But Vettel notes that the 16:8, which is often the most popular form of time restricted eating, can be easier to adhere to, as this method involves eating food within an eight-hour window and then fasting for 16 hours (such as from 7 PM until 11 AM) and a lot of the fasting occurs while sleeping.
How long to see intermittent fasting benefits?
This really varies from person to person, and depends on their diet and lifestyle overall, says Axe. “While intermittent fasting can be a beneficial strategy for improving your weight and health, you’ll ultimately get the most from it (and quickest results) if you eat a clean diet, sleep rough and stay active,” he reveals. If you do this, Axe says you can probably expect to start seeing some results within just 1-3 weeks.
“If you’re feeling good overall, perhaps you’re losing some extra weight and you’re noticing that your appetite and energy levels are adjusting well, then these are all signs that intermittent fasting is a good option for you,” explains Axe. He warns, however, if you’re feeling fatigued, moody, can’t sleep and are always hungry, then these are signs you should probably adjust things.
Connor notes that when starting an intermittent fasting routine, you may experience some initial reactions. “One of the easiest ways to know you are doing it right is that at first, you might feel very hungry and have these side effects which tend to diminish over the first few weeks,” she says. Additional early side effects can include:
- Feeling cold
- Feeling light-headed
- Difficulty concentrating
- Experiencing mood swings
- Less energy
- Bad breath
- Not being able to stop thinking about food
While these symptoms may be difficult to deal with, Connor says they do seem to go away over time. “And fortunately, after a month or so, people tend to not feel as hungry or experience these symptoms,” she explains.
And one final caveat: Ryan Andrews, RD, a principal nutritionist and advisor at Precision Nutrition, says there are a few groups who might want to check with their doctors before hopping into time restricted eating.
“Intermittent fasting is discouraged for women who participate in high amounts of physical activity, women who are pregnant, people with a history of disordered eating, people who are brand new to the world of nutritional changes, people who are chronically stressed, and people who don’t sleep well,” he says. Andrews explains that much of this is due to the potential for hormonal disruptions that can take place in the body when someone isn’t consuming enough energy or calories. In other words: Proceed with caution!
- Dr. Josh Axe, D.N.M., C.N.S., D.C., founder of Ancient Nutrition and DrAxe.com, author of the best-selling book KETO DIET the upcoming book Ancient Remedies, and host of The Dr. Axe Show
- Dr. Pamela Peeke, MD, MPH, FACP, FACSM, lifestyle medicine expert and chair of the Jenny Craig Science Advisory Board
- Sheri Vettel MPH, RD, LDN
- Brynna Connor, MD, board-certified family physician and pioneer in anti-aging and regenerative medicine, Healthcare Ambassador at NorthWestPharmacy.com
- Cynthia Thurlow, nurse practitioner, nutrition and intermittent fasting TED talker
- Dr. Michael Roizen, a Cleveland Clinic doctor and author of The What to Eat When Cookbook
- Ryan Andrews, RD, Principal Nutritionist and Advisor at Precision Nutrition
- Current Obesity Reports: “Intermittent fasting: Is it worth the wait?”
- Cell Metabolism:”Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even Without Weight Loss in Men with Prediabetes.”
- Nutrients: Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus