What Is Intermittent Fasting, and Is It Worth Trying?

You may have seen the trend of intermittent fasting picking up steam in recent years, with health and fitness enthusiasts praising it for helping them lose weight, simplify their lifestyles, and improve overall health. 

But what exactly is intermittent fasting?

Intermittent fasting is an eating plan that cycles between periods of eating and fasting. Some of the most popular approaches include:

• Alternate-day fasting: Eat a normal diet one day and either fast completely or have one small meal (less than 500 calories) the next day.
• 5:2 fasting: Eat a normal diet five days a week, and consume only 500 to 600 calories on two nonconsecutive days of the week.
• Daily time-restricted fasting: Also known as the Leangains method or 16/8, this calls for eating normally within an eight-hour window every day and fasting for the other 16 hours. For example, skipping breakfast and having your first meal at noon, with dinner at around 8 p.m.

Many people find the daily time-restricted method to be the simplest, most sustainable and easiest to follow. It’s also the most popular. 

Rooted in history

Studies suggest that fasting has been practiced throughout human evolution. Because ancient hunter-gatherers didn’t have access to things such as supermarkets, refrigerators, or food that was available year-round, they sometimes went long stretches without anything to eat. As a result, humans evolved to be able to function without food for extended periods. 

Researchers have found that fasting from time to time could lead to a significant decrease in developing disease, compared with those who eat six or more meals per day.

Fasting is also often done for religious or spiritual reasons, including in Islam, Christianity, Judaism, and Buddhism.

What are the health benefits of intermittent fasting?

Research indicates that fasting can help manage weight and help prevent or slow the progress of certain diseases. 

On the flip side, there are accounts that point to fasting as being dangerous, suggesting it's smarter to eat multiple smaller meals throughout the day as opposed to starving the body. Some of the negative effects of intermittent fasting commonly reported are: feeling hungry, irritable or fatigued, nutrient deficient, and experiencing digestive issues.  

The vast majority of research, though, points to the benefits of intermittent fasting outweighing the negative. Some of these include:

• Insulin levels drop. According to a study by the National Library of Medicine, blood levels of insulin drop significantly during fasting, which helps speed and facilitate the burning of fats in the body. By decreasing insulin dependency, fasting may also help ward against Type 2 diabetes. 
• Human growth hormone levels increase. Research suggests that the blood levels of human growth hormones increase dramatically during fasting — resulting in more effective fat burning and muscle gain.
• Cellular repair. When the body isn't working constantly to digest food, it can induce cellular repair processes — these include removing waste material, restoring function, and destroying cells that carry anomalies.
• Gene expression increases. Studies indicate that fasting can promote beneficial changes in several genes and molecules, helping protect against disease and promote longevity. 
• Increased thinking and memory skills. Intermittent fasting in tests seemed to boost working memory in animals and better verbal memory in adult humans. 

Frequently Asked Questions

Is intermittent fasting safe?

Generally speaking, yes. Intermittent fasting isn't for everyone, though, and people who suffer from diabetes or low blood pressure or have a history of heart disease should consult a doctor before trying fasting or diet methods. Pregnant women should also avoid fasting.

Are there side effects?

With any type of fasting, hunger is the main side effect. At the onset, you may also experience brain fog and fatigue as your body adjusts to longer periods without eating. Side effects should be gone within a month, according to the Mayo Clinic.

Keep in mind that intermittent fasting is meant to help you consume fewer calories in general — binging or eating massive amounts during eating periods may result in no weight loss at all, or even weight gain. Therefore, with any fasting or dieting method, discipline is key.  

Can I drink coffee or tea during fasting periods?

Yes, but technically you should be consuming only black coffee or tea without added sweeteners. There is a loophole: If you drink any beverage that has less than 50 calories, your body will remain in a fasting state. So adding a bit of cream or sugar to your morning brew is just fine. And as always, be sure to drink lots of water throughout the day to ensure your body remains well hydrated. 

Will fasting slow down my metabolism?

No. Studies show that short-term fasts actually help speed up metabolism (as much as 14%). Longer fasts (three or more days) can suppress metabolism and should be avoided. 

What can I eat during intermittent fasting?

During fasting periods, you should consume only drinks with few calories, such as water or (mostly) unsweetened coffee and tea. During eating periods, try to follow a healthy diet rich in whole grains, fruits, vegetables, and lean protein.

Is intermittent fasting right for me?

There is no clear-cut answer. While intermittent fasting may be a great option for some people, enabling them to feel healthier and more energized, it may not work as well for others. The only way to find out which group you belong to is to try it and see how you feel.