Fasting isn't for everyone, but it offers more health benefits than you might think

When it comes to losing weight, there are no shortage of unproven recommendations to choose from: fad diets like the carnivore diet or GOLO diet; juice cleanses and vitamin injections; plus a host of powders, shakes, pills, supplements and other weight-loss products are constantly being touted on social media and across the internet despite often not providing the benefits they are purported to have.

At the same time, many legitimate and proven diets such as the DASH diet and the Mediterranean diet are also commonly suggested - as are well-studied and important recommendations to limit sugar or salt intake, reduce excessive calories, and exercise more frequently.

Somewhere in between the two, intermittent fasting has been growing in popularity. It has captured the attention of doctors, dieticians, and even celebrities like Jennifer Aniston, Chris Pratt, Kourtney Kardashian, and Jimmy Kimmel, per People magazine.

But just because intermittent fasting has helped some people doesn't mean it's right for everyone. Here are the pros and cons of the practice.

What is fasting?

Fasting simply means to abstain from food or drink for a period of time - though water and zero-calorie beverages such as tea or black coffee are often permitted. When one engages in the practice, "the focus is not on what you eat, but when you eat," says Dr. Jesse Bracamonte, a family medicine physician at Mayo Clinic.

The length of time one fasts varies and can mean skipping one meal or going without food and only drinking small amounts of liquid for several days at a time. Such variations in duration are usually determined by one's reasons for abstaining from food in the first place.

For instance, fasting is a common practice in many religions including Judaism, Islam, and Christianity. Members of the Church of Jesus Christ of Latter-day Saints are taught to go without food or drink for two consecutive meals one day every month. And Roman Catholics, Lutherans, Presbyterians, and Methodists, practice fasting on and off during the 40 days of lent each year to commemorate the 40 days Jesus Christ fasted in the Bible.

Beyond religious motivations, patients are asked by doctors to fast 6-12 hours before getting surgery or undergoing procedures such as colonoscopies.

But intermittent fasting is generally motivated by weight-loss goals or health interests and varies in length of time accordingly. One of the most popular methods of intermittent fasting is doing so "for a full 24 hours once or twice a week," says Bracamonte. The "5:2" method means eating normal for 5 days a week, then restricting calorie intake to 500 to 600 calories the other 2 days of the week. The "16:8 method," or the Leangains diet, is more continuous and recommends fasting for 16 hours a day, then eating all meals during an 8-hour window only.

Is fasting good for you?

Following any of these forms of intermittent fasting can have benefits - so long as some considerations are kept in mind. A New England Journal of Medicine study shows a host of advantages of intermittent fasting that include improved blood pressure and resting heart rate, enhanced metabolic health, increased cognitive function, and the burning of fat. Other research has shown similar advantages.

These benefits occur, in part, "as cells throughout the body and brain respond to intermittent fasting by improving their function and ability to cope with stress and counteract disease processes," says Mark Mattson, a neuroscientist at Johns Hopkins Medicine who has studied intermittent fasting for 25 years and has co-authored much of the research on the topic. He adds that one of the ways the body helps with healthy weight management is by exhausting sugar stores and burning fat after going many hours without food - a process he calls "metabolic switching."

While more obvious, people often lose weight when engaging in the practice "mainly due to consuming fewer calories," says Duane Mellor, a registered dietitian and the lead for evidence-based medicine and nutrition at Aston Medical School in England.

Along with helping people this way, he says there is also some evidence that intermittent fasting might also help with insulin resistance due to hormonal changes that occur when the body is temporarily deprived of food. "It is also thought that cellular repair might be enhanced when fasting," adds Bracamonte. Cellular repair allows the body to better heal from illness and injuries and rejuvenates tissue associated with aging.

How many times a week can you fast?

Despite such benefits, intermittent fasting isn't for everyone. Some people engaging in the practice experience fatigue, headaches, or irritability - though such symptoms often lessen over time as your body adjusts to caloric intake changes.

Mellor says that some people they may also struggle to eat normally on non-fasting days, which is why "it has been suggested that this could lead to binging-type behaviors - but such research isn’t conclusive." It's also possible to lose out on important nutrients your body needs if you engage in the practice extremely or too often.

Mattson adds that randomized controlled trials so far have been focused on adult women and men - studies that "have not revealed any harms of intermittent fasting" in those groups. But "there have not been trials in children, pregnant women, or elderly frail people - so they should be cautious when engaging in the practice and should consult with their doctor before doing so," he advises.

For people who want to try out intermittent fasting, "it is advisable to start gradually, listen carefully to your body, and pay attention if you start feeling unwell," suggests Bracamonte. "And plan your meals ahead of time to make sure you are getting the adequate amount of nutrients your body needs."

This article originally appeared on USA TODAY: What is fasting?