What Is Intermittent Fasting?

Intermittent fasting — periods of eating and fasting — continues to grow in popularity. And it may be more than a fad, with more data rolling in that may show it helps with weight management, blood pressure and more.

Registered dietitian Julia Zumpano, RD, LD, helps us understand intermittent fasting schedules and how this eating plan may benefit your health and wellness goals.

What is intermittent fasting?

Intermittent fasting is when you alternate between eating and fasting. This type of eating is often described as “patterns,” “cycles” or “schedules” of fasting.

Intermittent fasting isn’t about starving yourself or dieting — it’s about cutting way back on calories for short time periods (FYI: You can drink water and other beverages, like black coffee and tea, during fasting periods).

Fasting can regulate eating habits and decrease your body’s insulin production, which, in turn, may help reduce cravings, specifically for snack foods. When it comes to how to intermittent fast, you want to maintain proper nutrition in your overall diet and not put yourself at unnecessary risk.

“Weight loss is never a one-size-fits-all approach,” emphasizes Zumpano. “Intermittent fasting may be sustainable for some people, while others find that this approach just isn’t for them.”

Intermittent fasting schedules

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There are several effective approaches, but it all comes down to your personal preference, medical history and which method is best for your body.

“If you want to give intermittent fasting a try, be prepared to figure out what works best for you,” says Zumpano. “It might take some trial and error first.”

Ready to explore your options? Zumpano explains some of the most popular types of intermittent fasting.

The 16/8 or 14/10 method

In this time-restricted method, you have set intermittent fasting times and specific windows where you can eat. For example, you fast for 16 hours of the day and are able to eat for only eight hours of the day.

As most people already fast while they sleep, this method is popular.

“It’s convenient, as you extend the overnight fast by having breakfast later (brunch, anyone?) and starting dinner a little earlier,” says Zumpano. “This form of fasting is a safer bet for many people who are interested in trying intermittent fasting for the first time.”

Some of the most common fasting windows are:

• The 16/8 intermittent fasting method: Only eating between 11 a.m. and 7 p.m.
• The 14/10 intermittent fasting method: Only eating between 9 a.m. and 7 p.m.

Zumpano suggests fasting most days to see benefits.

If you’re very active or if you wake up hungry for breakfast, you may need to make some adjustments. But Zumpano says that it’s important that the majority of your calories are taken in before it’s dark out. She says to plan your fast to begin at least three hours before bedtime.

“Nighttime snacking commonly consists of calorie-dense, low-nutrient snack foods, which can spike blood sugar and lead to excess calories and carb consumption,” she adds. “Most nighttime eating is habitual.”

If you’re actually hungry, Zumpano suggests adding more protein and fiber to your day, including a mid-afternoon snack, like plain Greek yogurt and berries. Avoid eating after dinner to give your blood sugar time to normalize before going to bed.

The 5:2 method

This twice-a-week approach to intermittent fasting focuses on capping your calories at 500 for two days a week. During the other five days of the week, you maintain a healthy and normal diet.

On fasting days, this approach usually includes a 200-calorie meal and a 300-calorie meal. It’s important to focus on high-fiber and high-protein foods to help fill you up and keep calories low when fasting.

You can choose your two fasting days (say, Tuesdays and Thursdays), as long as there is a non-fasting day between them.

Alternate-day fasting

This variation involves “modified” fasting every other day. For instance, limit your calories on fasting days to 500 ― or about 25% of your normal intake. On non-fasting days, resume your regular, healthy diet. (There are also strict variations to this approach that include consuming 0 calories on alternate days instead of 500.)

An interesting note: One study showed people following this pattern of intermittent fasting for six months had significantly elevated LDL (or “bad”) cholesterol levels after another six months off the diet.

“This method of fasting isn’t recommended because it’s very restrictive, not sustainable for long-term use and has the potential to lead to nutrient deficiencies,” warns Zumpano.

“Consistently not meeting your caloric needs can inhibit weight loss by decreasing your metabolism and causing your body to go into ‘starvation mode.’”

Eat: stop: eat method

This 24-hour method involves fasting completely for a full 24 hours. Often, it’s only done once or twice a week. Most people fast from breakfast to breakfast or lunch to lunch. With this version of intermittent fasting, the side effects can be extreme, such as fatigue, headaches, irritability, hunger, low energy, nausea, weakness and difficulty concentrating.

If you follow this method, you should return to a normal, healthy diet on your non-fasting days. The method is cautioned by healthcare professionals due to insufficient research and an increased likelihood of negative symptoms. Going too long without eating isn’t better, as it may encourage your body to store more fat in response to starvation.

Is intermittent fasting healthy?

Research shows there could be some benefit to intermittent fasting. For example, some people may turn to intermittent fasting for weight loss, while others may use it to help with medical conditions, like irritable bowel syndrome (IBS) and high blood pressure.

Intermittent fasting benefits

Intermittent fasting may result in the following benefits:

• Decreases inflammation
• Decreases blood triglycerides
• Decreases appetite
• Improves blood sugar
• Improves blood pressure
• Improves gut health
• Improves immune system
• Improves concentration
• Improves sleep quality
• Decreases signs of aging
• Reduces weight

“Intermittent fasting has been shown to have several positive health outcomes, from reducing insulin, appetite and inflammation to improving health conditions such as high blood pressure, high cholesterol and IBS,” shares Zumpano.

Intermittent fasting risks

Intermittent fasting isn’t safe for some people, including:

• People who are pregnant or nursing
• People who are malnourished
• People with hypoglycemia
• People with certain chronic diseases
• Children

You should also be cautious if you’re experiencing perimenopause, as fasting can impact your hormones.

“If you have a history of an eating disorder or are currently being treated for one, you shouldn’t attempt any sort of fasting diet without medical supervision,” advises Zumpano. “Intermittent fasting has also been known to increase the likelihood of binge eating or orthorexia in some people because of the restriction.”

If you’re interested in trying intermittent fasting, you should also be aware of some not-so-pretty side effects. It can be associated with irritability, low energy, persistent hunger, temperature sensitivity, and poor performance at work and in other activities.

Tips when starting intermittent fasting

While more research is needed on the benefits of intermittent fasting and how it may affect our health long term, there’s lots of promising data around it. And it may be something you’d like to try.

If you’re getting started with intermittent fasting, Zumpano offers the following advice:

• Have a routine. Keep a similar eating and fasting window on the days you choose to fast.
• Watch what you drink. To maintain a fasting state, you must not consume any foods or drinks with calories. Zumpano says water, carbonated water, black coffee and unsweetened teas are all acceptable when fasting.
• Avoid or limit artificial sweeteners. Artificial sweeteners, like saccharin, aspartame and sucralose, have the potential to remove you from a fasting state.
• Consider electrolytes. Choose electrolyte drinks, powders, tablets or water enhanced with electrolytes. Electrolytes can aid in decreasing some of the negative side effects of fasting, like lightheadedness, fatigue and decreased blood pressure.

Key takeaways

Ultimately, you should contact a healthcare provider and discuss intermittent fasting before you start. They can offer the right guidance on whether any of these intermittent fasting options are right for you.

Also, keep in mind that if you choose to try fasting, your medication regimen may be affected. Talk to your healthcare provider before you make any changes to the times you take your medications.

“Fasting can be a great way to improve your health, but if done improperly, it can lead to negative health outcomes,” warns Zumpano. “Avoid extreme forms of fasting that aren’t sustainable. Choose a method that you can stick with, feel great about and meet your nutrient needs with. Fasting is a great way to reduce those not-so-healthy foods and focus on nutrient-dense foods first and foremost.”