Intermittent fasting has fast become the most popular nutrition trend in America. In 2020, it surpassed both the keto diet and clean eating approach to nutrition, according to a survey by the International Food Information Council. About 10% of the more than 1,000 people surveyed were proud intermittent fasters, going for long stretches without a bite to eat.
If you haven’t tried intermittent fasting (IF) for yourself, you’ve likely heard buzz about it in the wellness world. There is a lot of information out there, so how do you know if intermittent fasting really works? And more importantly, will it work for you? We answer five of the biggest burning questions for IF beginners.
1. What Is Intermittent Fasting?
Put simply, intermittent fasting is a practice that alternates between periods of eating and fasting. With IF, “individuals are choosing not to consume any food or caloric intake other than beverages that don’t have calories or sweeteners,” says Dr. Ryan Greene, DO, MS, Lifeforce Clinical Advisor and Co-Founder and Medical Director at Monarch Athletic Club.
In most forms of intermittent fasting, water, black coffee, and unsweetened tea are allowed during fasting periods. During eating windows, you can choose what types of foods to fuel your body with.
“Many people want to think of IF as a ‘diet’ or fad, but it is anything but that,” says Shana Hussin, RDN, a Registered Dietitian and intermittent fasting expert. “It is a potent therapy to allow your body healing and digestive rest.”
2. What Are the Potential Benefits?
While every individual will respond differently, here are a few of the science-backed perks you may experience with IF.
Optimizes Cell Function
Intermittent fasting gives the body a break between meals, which may help cells function more efficiently. “Our cells have basic programming that allows them to generate energy to execute whatever function they’re designed for,” says Dr. Greene. The idea is that the strongest cells will thrive, while those that aren’t operating at their peak will be eliminated to make room for higher performing replacements. However, continuously fueling our cells with food may interrupt that natural process, explains Dr. Greene.
“We often eat when we’re hungry, bored, or because food is available. There is a belief that those practices reduce our baseline cellular function,” Dr. Greene says. “It is believed that intermittent fasting may help the body become more resilient and optimize the highest performing cells.”
And when it comes to our long-term wellness, cell optimization translates to enhanced healthspan and longevity. According to research, periodic fasting helps protect against chronic disease and may delay the effects of aging.
Promotes Weight Loss
Weight loss may be one of IF’s biggest wins. “Weight management is where people have found the most success with intermittent fasting,” says Dr. Greene.
A review of 40 studies found that IF was effective for weight loss, with an average loss of 7 to 11 pounds over 10 weeks. How does it shed pounds? Scientists are still investigating, but there is some evidence that IF can optimize fat-burning hormones and enhance metabolism.
“Different from chronic calorie restriction that damages the metabolic rate, human growth hormone rises during fasting, protecting muscle mass and promoting fat burning,” says Hussin. With her own clients, she has observed that “body composition improves significantly, and improvements are sustainable and long-term as long as the lifestyle changes are kept up with.”
Still, the research in this area is mixed. Another recent study found no difference between time-restricted eating and simply restricting calories.
“Is it the intermittent fasting alone or the fact that people are consuming less calories that contributes to weight loss? That is something that still needs to be investigated more,” says Dr. Greene.
He notes that mindset and lifestyle factors may play a key role in intermittent fasting’s success. “When people have more structure and routine, the body tends to do better,” he says. “When my patients stick to a regimen of time-restricted eating, they are more conscientious about portions and nutrition. They are also thinking more about exercise, sleep, and consuming less alcohol.”
Improves Insulin Sensitivity
“Fasting is the most potent strategy to bring insulin levels down quickly,” says Hussin, who runs a group program to help patients reverse their insulin resistance.
Research shows that intermittent fasting may reduce blood sugar levels and insulin resistance, which is especially helpful for those at risk of developing type 2 diabetes. In one study, researchers found that even without weight loss, intermittent fasting increased insulin sensitivity in men with prediabetes.
As your fasting time goes up, your body’s inflammation may go down. “IF is anti-inflammatory, so it brings overall inflammation down in the body over time,” notes Hussin. “This helps to heal metabolic issues — especially pre-diabetes and type 2 diabetes — and fatty liver.”
Research found that intermittent fasting reduced levels of pro-inflammatory monocytes, white blood cells that play a role in the immune system. High levels of monocytes can be caused by acute stress and inflammation, and have been linked to certain inflammatory and autoimmune conditions.
Intermittent fasting gives your digestion a rest — and it may give you better rest, too. “Almost all my clients see improvement in sleep and energy levels,” says Hussin. Research backs this up, showing that intermittent fasting may improve sleep quality by reinforcing circadian rhythms, our body’s natural sleep-wake cycle.
Additional studies show that late-night eating can disrupt sleep patterns. As Hussin notes, “Our bodies do not like to be digesting food all the time, especially at night. When we give our bodies a break, amazing healing happens!”
3. What Type of Intermittent Fasting Is Right for You?
Tempted to try IF and reap these benefits? First, you need to consider the different approaches and possible eating schedules. Some of the most well-known types are:
Time-restricted eating: This is the most popular IF method, according to Hussin, since you get to choose your eating window. For example, if you’re following a 16/8 pattern, you fast for 16 hours and eat within an 8-hour window (think: eating from 10 a.m. to 6 p.m.). You can adjust these time windows — the 14/10 method is also popular.
The 5:2 Method: In this style, you stick to a normal healthy diet five days a week and cut back to 25 percent of your usual caloric intake on the other two days. (So, for example, a person who regularly eats 2,000 calories a day would eat 500 calories on fasting days.)
The 24-Hour Fast: This method involves fasting completely for 24 hours once or twice a week. For example, you may eat dinner at 5 p.m. one day and break your fast at 5 p.m. the following day.
Alternate Day Fasting: As the name suggests, this method means fasting every other day. Some versions of this plan allow about 500 calories on fast days; others suggest consuming close to zero calories. “This is an advanced strategy I recommend for those with more severe insulin resistance or metabolic disease,” Hussin says.
4. How Do You Get Started?
Dr. Greene’s advice is to “start low and go slow.” In the beginning, choose a shorter fasting window that you can successfully stick with. “If things are working and you’re getting close to your goals but haven’t achieved them, you can get a little more advanced and lengthen your fasting window,” he says.
He also recommends that you start by reflecting on your health goals and how intermittent fasting can fit into your lifestyle. “Ask yourself, ‘What do I want to achieve? How many calories do I need to get there and also maintain an active life? How am I going to make sure I get the appropriate amount of calories in a certain time frame?’ You have to do some preparation.”
Dr. Greene and Hussin both stress that intermittent fasting is a lifestyle shift, not a quick fix. “Give it time, 30 days minimum,” Hussin advises. “Some people try one method for a week, see little progress, and think it hasn't worked. IF is a lifelong strategy.”
5. Who Shouldn’t Try Intermittent Fasting?
Keep in mind, intermittent fasting isn't right for everyone. “There are some subsets of people who should not practice IF, such as those who are pregnant or breastfeeding, those with an active eating disorder, or those under a terrible amount of stress (physically or mentally), who may not handle fasting well,” says Hussin. Dr. Greene also warns that intermittent fasting may not be appropriate for people with diabetes who are insulin dependent or are on certain anti-diabetic medications. Consult with your physician before starting intermittent fasting or any new dietary plan.
The Bottom Line
Will intermittent fasting work for you? Only you can answer that for sure, keeping in mind your individual goals and lifestyle long-term. “I always tell patients that the best plan for you is going to be the one you can stick with,” says Dr. Greene.
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This article was medically reviewed by:
Ryan Greene, DO, MS, Board Eligible Integrative and Preventive Medicine Specialist
Vinita Tandon, MD, ABIM Board Certified in Endocrinology and Metabolism