Intermittent Fasting Explained: Benefits and How To Do It Safely

The diet and nutrition world is full of trends, and one that’s been gaining momentum is intermittent fasting.

As intermittent fasting has grown in popularity, more data is rolling out that, in some cases, might support intermittent fasting as more than just a fad.

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

What is intermittent fasting?

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

Intermittent fasting isn’t about starving yourself — 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).

The belief is that your body becomes satisfied with smaller portions while also reducing cravings for unhealthy snack foods. That is, as long as you maintain a healthy diet while trying it all out.

There are several effective approaches, but it all comes down to personal preference.

“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.”

Some people find it easy to fast for 16 hours and confine meals to just eight hours of the day, such as 9 a.m. to 5 p.m., while others have a hard time and need to shorten their fasting window.

Intermittent fasting benefits

So, does intermittent fasting work? And is it healthy?

Some people may try intermittent fasting to help with weight management, while others may use it to help with medical conditions like irritable bowel syndrome and high blood pressure.

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.

Fasting schedules

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.”

If you want to try intermittent fasting, you’ll first need to figure out how you’re going to incorporate this style of eating into your life, especially when it comes to things like social events and staying active, she advises.

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 skipping breakfast later (brunch, anyone?) and starting dinner a little earlier. This form of fasting is a safer bet for many people who are interested in trying intermittent fasting for the first time,” says Zumpano.

Some of the most common fasting windows are:

• The 16/8 method: Only eating between 10 a.m. and 6 p.m.
• The 14/10 method: Only eating between 9 a.m. and 7 p.m.

Zumpano suggests fasting for most days to see benefits.

Again, finding the right eating and fasting windows for this method might take some trial and error, especially if you’re very active or if you wake up hungry for breakfast. 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 sugars and lead to excess calories and carbs,” she adds. “Most nighttime eating is habitual.”

If you’re actually hungry, Zumpano suggests adding more protein and fiber to dinner. 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. Be sure to eat the same amount of food you normally would on non-fasting days.

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.

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 and low energy.

If you follow this method, you should return to a normal, healthy diet on your non-fasting days.

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.

People who menstruate, such as pre-menopausal females, should be cautious, too, 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 work and activity performance.

Bottom line?

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.

Ultimately, you should contact your healthcare provider and discuss intermittent fasting before you get started. Your healthcare provider knows your health better than anyone else and 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 with 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.”