Is Intermittent Fasting Right for You?

Intermittent fasting (IF) remains one of the most popular eating patterns among Americans following a diet plan, even though its long-term benefits are still unknown.

It’s a method of calorie restriction based on timing. Unlike other eating patterns, IF is based on when you eat, not what you eat.

This eating pattern has become more mainstream as many celebrities and influencers swear by it, said Caroline Susie, RDN, LD, a registered dietitian and spokesperson for the Academy of Nutrition and Dietetics.

“According to the internet, it can solve everything, right?” Susie said.

The research on IF is mixed. A new study showed that time-restricted eating may help people with obesity lose weight, while another found that intermittent fasting had no significant impact on weight loss.

Most of the other existing studies that support this eating pattern were conducted on animals, while the few studies involving humans have been short and often include a small sample size.

“We want to be careful,” Susie said. “The research is just pretty limited.”

Intermittent Fasting Plans

Although the research on IF is mixed, some people still follow a schedule to support their weight loss goals or to maintain their fitness level.

There are three main IF schedules:

1. Alternate-day Fasting: Rotate between days of eating and days of fasting. On fasting days, you’re not allowed to consume any calories aside from water, black coffee, or tea. On non-fasting days, you can eat anything you want.
2. Modified Fasting: There are different approaches to this, such as fasting two days a week (called the 5:2 fast) and eating normally for the other five days, restricting calories to a certain percentage of your normal intake on fasting days, or restricting calories to a certain number (e.g., 500 calories) on fasting days.
3. Time-restricted Fasting: This means fasting for a set number of hours, which can vary from eight to 12 hours a day. Many people try to include sleep time in their fast to make this more manageable.

Flexibility in Intermittent Fasting

The ability to individualize this eating pattern may be one reason it’s so popular compared to other restrictive diet plans.

Carianne Hixson, an administrative and creative coordinator based in Montclair, New Jersey, started trying intermittent fasting in 2019. She now follows a time-restricted fasting schedule where her “eating window” is between 11 a.m. and 7 p.m.

“I chose my window of eating based on my work schedule and my relationship with myself,” Hixson told Verywell.

Justin Kilgore, PT, DPT, a physical therapist based in Fort Collins, Colorado, has followed a time-restricted schedule on and off for the past six years. He said this eating pattern made sense with his work schedule and “natural eating tendencies,” but traveling can make it challenging to adhere to the schedule.

“I have experienced times where I have missed my eating window,” Kilgore said. “During those times, I’ll either break my fast for the day, or I’ll switch to a 24-hour fast then return to normal the next day.”

Is Intermittent Fasting Safe?

For most healthy adults, time-restricted eating is safe. IF can help people “become more cognizant of a healthy eating pattern,” but they do have to be cautious about how they practice it, said Sharon Smalling, MPH, RD, LD, a clinical dietitian specialist at the Memorial Hermann Hospital in Texas.

Although IF doesn’t restrict food choices, it’s still important to consider your overall diet quality.

“If you don’t change your food choices, it’s really not going to make any difference,” Smalling said.

People with certain conditions, such as diabetes, should consider talking to a trusted healthcare provider before trying out IF, she added. For people who use insulin, fasting might lead to hypoglycemia, a condition that occurs when blood sugar level drops too low.

According to Susie, IF is not recommended for children or people who are pregnant or breastfeeding. Some experts are also cautious about alternate-day and modified fasting schedules because these plans could lead to decreased concentration, low energy levels, or hunger pains.

For now, Smalling said, a lot more long-term research needs to be done to confirm the benefits of this eating pattern.