Here’s Everything You Need to Know and Consider About Intermittent Fasting

Some doctors say the risks outweigh the benefits.

By now, you’ve probably heard about intermittent fasting. Though fasting is nothing new, and it’s long been a part of various religious and cultural practices, intermittent fasting has become especially buzzy and has taken over diet culture in recent years. It’s also been touted by many wellness influencers as well as celebs like Halle Berry and Jennifer Aniston. In 2019, Today Show anchors Hoda Kotb and Jenna Bush Hager even weighed themselves on live television ahead of trying intermittent fasting. So, it’s hard not to be curious about it.

However, as with any wellness trend—especially one that asks you to put restrictions on eating—it’s important to do some careful consideration before hopping on the bandwagon. So, we tapped health experts to learn more about this type of fasting, its benefits and risks, and how it can affect the body and mind. Let’s get into it.

What is intermittent fasting?

Intermittent fasting is an umbrella term for several different eating patterns that cycle between fasting and eating. In contrast to more standard diets, which focus on what to eat, intermittent fasting is all about when to eat.

“Technically, everybody intermittent fasts when they go to bed at night, because you don’t eat while you are sleeping,” registered dietitian Amy Kubal, explains to HelloGiggles. “That’s [considered] a fast. But what people are doing [on the intermittent fasting diet] is extending that window, and there are so many different versions of intermittent fasting.”

For example, some people will stop eating before they go to bed and start again with a late breakfast around 11 a.m. Others will not eat after 6 p.m., not eat before 2 p.m., or practice alternate-day fasting where they fast for an entire day, every other day.

Many people use intermittent fasting as a weight loss method and it has shown to be effective for some. Erika Schwartz, MD, an internist who specializes in disease prevention, explains why. “When food is restricted, the body has to instead use its reserves: fat stores [to get energy],” Dr. Schwartz says. “Instead of using available glucose from carbohydrate intake, the body uses fat stores, which causes weight loss.”

Temporarily switching the body’s source of energy, also called metabolic switching, has also been shown to produce overall health benefits, such as suppressing inflammation, reducing the resting heart rate, building resistance to stress, and improving brain health.

Intermittent fasting schedules:

For those who decide to start intermittent fasting, there’s a bit of a “choose your own adventure” element to it. Below are some of the popular methods.

  • The 16/8 method: This method involves fasting for 16 hours and eating during only an eight-hour window each day. So, if you finished your last meal at 7 p.m., you would wait 16 hours, or until 11 a.m. the next day to eat your next meal, then stop eating for the day again at 7 p.m.
  • The 5:2 diet: This method involves eating as you normally would for five days a week and restricting food intake to 500 to 600 calories for two days out of the week.
  • Eat-stop-eat: This method involves fasting for two 24-hour periods in a week and eating normally on other days of the week.
  • Alternate-day fasting: Like the eat-stop-eat method, alternate-day fasting involves some days of eating as normal and some days of fasting, only these periods are alternated every other day.
  • The warrior diet: This method involves fasting for about 20 hours a day and then eating one large meal at night during a four-hour period.

Fasting also means different things for different people. While some may restrict all eating during fasting periods, only intaking beverages like coffee and water, others may eat small amounts of fruits and vegetables during fasting periods.

What happens to your body when you fast?

So, there are a number of different intermittent fasting methods and strategies out there—but is it actually good for you? Like everything in health and wellness, there’s no one-size-fits-all answer and intermittent fasting can have different effects on different people. This is why it’s important to consider both the good and bad ways that restricted eating patterns can affect your body and mind before trying it out for yourself.

Intermittent fasting benefits:

Researcher, psychologist, and wellness expert Christina Rahm, M.D. has mixed opinions on intermittent fasting. However, she noted some of the “incredible benefits” of intermittent fasting, including its potential to “boost memory, improve heart health, improve endurance levels, prevent obesity and diabetes, and reduce tissue damage.” As studies have shown, these changes are due to the process of metabolic switching mentioned above.

A study by Johns Hopkins neuroscientist Mark Mattson, Ph.D., also highlighted how the metabolic switch caused by intermittent fasting can aid the body’s defense against diseases.

“Many things happen during intermittent fasting that can protect organs against chronic diseases like type 2 diabetes, heart disease, age-related neurodegenerative disorders, even inflammatory bowel disease and many cancers,” he said, according to Hopkins Medicine.

However, while these benefits still need to be studied on a large scale, it’s important to consult with your doctor as these benefits might not appear for everybody.

Intermittent fasting risks:

Jessica Cording, MS, RD, CDN, explained in an article for Shape, however, why she isn’t a fan of the diet trend. “While research has shown some potential health benefits of intermittent fasting, as a dietitian and health coach who focuses on sustainable lifestyle approaches to wellness, I can’t quite get on board with recommending that someone just not eat,” she wrote. “Fasting can be a slippery slope to unhealthy habits and a screwy relationship with food.”

This is why many health experts, including Dr. Rahm and Dr. Schwartz, say that intermittent fasting can be dangerous for people with eating disorders or can cause a risk in someone developing one. In addition to creating or perpetuating an unhealthy relationship with food, the practice can also have negative effects on mental health. “Intermittent fasting can mess with mood, causing feelings of irritability and anger, increase anxiety, cause difficulty sleeping, and feelings of loneliness,” Dr. Rahm says.

Kubal adds that intermittent fasting can add additional stress, causing more harm than good. “For anyone under a lot of stress, who is not sleeping well, or your job is super stressful, or you have a physical job, adding another stressor is going to make things worse before it gets better,” Kubal says.

Intermittent fasting is also not recommended for anyone under the age of 18, or those with chronic conditions, hormone issues, or diabetes, since these individuals have higher caloric needs on a daily basis and can be put at higher risk when calorie intake is restricted.

Whether you feel personally suited to intermittent fasting or not, however, you should always consult a doctor before making a drastic change in your eating patterns. Most importantly, Dr. Schwartz adds, “If you do not feel well while you are fasting, then stop.”

Kubal echoes this sentiment, adding that it’s important to listen to your own body, and not to beat yourself up about intermittent fasting success stories you read online. “Just because it says it’s good somewhere on the internet doesn’t mean it’s good for you,” she says. “Everybody is different, and your body knows more than the internet ever will.”

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