What is Intermittent Fasting?

If you’re hearing more people tout the benefits of intermittent fasting, you’re not alone. The weight-loss diet  — which calls for reducing your calorie intake a couple of days a week or during specific times of day — is popular among health bloggers and personal trainers as well as celebrities like Chris Martin and Jennifer Aniston.

But how exactly does it work and who can benefit from it?

Fasting is when you choose to go without food or drink, or both, for a period of time. It’s been around for thousands of years and can have benefits, says Jamie Leskowitz, a registered dietitian at NewYork-Presbyterian/Columbia University Irving Medical Center.

“You can also think of it as eating more in line with your circadian rhythm,” she says. “From an evolutionary perspective, these days we work all different hours and have access to on-demand food delivery and 24-hour stores, which wasn’t how our eating patterns were. We can shift our eating patterns to give our bodies a break and eat more mindfully.”

In intermittent fasting, you limit food according to a pre-determined schedule, with the goal of reducing calorie intake and losing weight. “Intermittent fasting focuses on when you eat, with regular periods of eating and fasting,” says Dr. Judith Korner, founder and director of the Metabolic and Weight Control Center at NewYork-Presbyterian/Columbia University Irving Medical Center.

Health Matters spoke with Jamie and Dr. Korner, who is also a professor of medicine at Columbia University Vagelos College of Physicians and Surgeons, to learn more about the eating plan.

What are types of intermittent fasting schedules?
Jamie: There are many different types of intermittent fasting. Some methods include:

• Alternate-day fasting, where somebody may eat very few calories every other day.
• 5:2 approach, where somebody may eat very few calories two days of the week and eat as they usually would the other five days.

Other ways include a time-restricted period in which you’re eating over the course of eight or 12 hours during the day, and then you have a longer fasting period in-between.

What’s most important is what’s going to work best for you and your schedule.

Dr. Korner: It’s about a person’s individual lifestyle.

For example, if Wednesdays and Fridays are busy days for someone, they may not have time to cook and could choose those as 500-calorie days where they consume less. But there isn’t a one-size fits all or miracle diet. The important thing that people need to ask is, ‘Will this be something that I can follow life-long?’

What are the benefits of intermittent fasting?
Jamie: Some researchers believe that a prolonged fasting period may be beneficial for conditions such as high blood pressure and cholesterol, and help with liver and heart health. But it’s challenging to determine if the health benefits are solely from the weight loss, because we’re reducing total calorie intake, or if there are additional benefits due to the prolonged fasting period.

Dr. Korner: When you lose weight, whether it’s through intermittent fasting, daily calorie restriction or other ways, you’re going to improve metabolically. Your insulin levels are going to improve, and you may reduce your risk of developing conditions such as diabetes, heart and liver disease, and cancers.

But it should be noted that those improvements come with any type of weight loss, no matter the method.

What can you eat during intermittent fasting?
Dr. Korner: There’s no specific menu, but whatever diet you do, it should be balanced with healthy foods.

There’s more and more data showing the benefits of unprocessed foods. The best approach, no matter what we do, is make sure we’re eating enough portions of leafy greens, fruits, vegetables, and healthy proteins like beans.

Are there people who shouldn’t try it?
Jamie: Fasting is not appropriate for people who are pregnant or breastfeeding. Before embarking on an intermittent fasting program, it’s important to meet with a dietitian or health professional who can help you create a safe and healthful eating pattern.

What should people know before starting intermittent fasting?
Dr. Korner: It’s important to keep in mind that it’s not that different diets don’t work, it’s that everyone is different. Find the type of diet that works for you, that satisfies your cultural needs, your cravings, hunger, and ability to cook and shop.

Jamie: What’s most important is having a balanced, healthful approach that works you and your lifestyle. The best diet is the one that you can adhere to and is sustainable.

I suggest creating a regular eating pattern that includes satisfying and enjoyable meals and snacks with nutrient-dense, whole foods. But keep in mind that this will likely not look identical for everyone.

Is it realistic to stop eating at 6 p.m. for a whole year and beyond? It’s not about a perfect eating plan forever, but eating healthily in a way that feels good to you and can help you reach your health goals. Many people benefit from a more structured plan, others prefer more flexibility and less rigidity. Knowing yourself and what’s most realistic is key.