Intermittent Fasting: 4 Different Types Explained

Can this ‘pattern’ style of eating be right for you?

Woman drinking healthy smoothie during fasting

If you thought fasting was just for religious purposes, think again. A newer phenomenon in the weight loss world called Intermittent Fasting (IF) is growing into a popular health and fitness trend.

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

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

“If you want to give IF a try, be prepared to figure out what works best for you,” says registered dietitian Anna Taylor, MS, RD, LD, CDE. “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, explains Taylor.

But is intermittent fasting good for you?

While some research has shown the benefits of IF, such as weight loss, lower blood pressure and improved metabolic health, more investigation is still needed, especially regarding long-term outcomes of IF. There is also the aspect of sustainability. Severely restricting calories or not eating for long periods at a time isn’t for everyone. Some research even shows that those who do intermittent fasting don’t usually stick with it as compared with those trying to lose weight on more traditional diets.

Still, IF has been shown to be an effective form of weight loss – but so have other options like eating a well-balanced diet paired with exercise. One study suggests that IF is not more effective at supporting weight loss or improving blood sugars than other well-balanced approaches.

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

If you want to try IF, you’ll first need to figure out how you are 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? Here Taylor explains some of the most popular IF methods.

1. The twice-a-week method – 5:2

This approach to IF 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, but to also keep calories low when fasting.

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You can choose whichever 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.

2. 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.)

Interesting finding of note: One study showed people following this pattern of IF for six months had significantly elevated LDL (or bad) cholesterol levels after another six months off the diet.

3. Time-restricted eating (example: 16/8 or 14/10 method)

In this option, you have set fasting and eating windows. For example, you fast for 16 hours of the day and are able to eat for only eight hours of the day.

Since most people already fast while they sleep, this method is popular. It’s convenient as you extend the overnight fast by skipping breakfast and not eating until lunch. Some of the most common ways?

  • 16/8 method: Only eating between 11 a.m. and 7 p.m. or noon and 8 p.m.
  • 14/10 method: Only eating between 10 a.m. and 8 p.m.  

This method of IF can be repeated as often as you’d like or even done once or twice a week – whatever your personal preference is.

Finding the right eating and fasting windows for this method might take a few days to figure out, especially if you’re very active or if you wake up hungry for breakfast.

“This form of fasting is a safer bet for many people who are interested in trying IF for the first time,” says Taylor.

4. The 24-hour fast (or eat: stop: eat method)

This method involves fasting completely for a full 24 hours. Often times, it’s only done once or twice a week. Most people fast from breakfast to breakfast or lunch to lunch. With this version of IF, 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 is not a magic pill

Whether you are doing IF, keto, low carb, high protein, vegetarian, the Mediterranean diet – you name it – it all comes down to the quality of your calories and how much you’re consuming.

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The bottom line with IF? Although the jury is still out and long-term effects are still being studied, it’s crucial to eat a healthy, well-balanced diet while following IF.

You can’t eat junk food and excessive calories on non-fasting days and expect to lose weight, says Taylor.

Side effects & risks

Intermittent fasting is not safe for some people, including pregnant women, children, people at risk for hypoglycemia, or people with certain chronic diseases.

“If you’re at risk for an eating disorder, you shouldn’t attempt any sort of fasting diet,” advises Taylor. “IF has also been known to increase the likelihood of binge eating in some people because of the restriction.”

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

Where to start?

Consider a simple form of IF when starting out.

“If you want to try IF, I would recommend starting with a more moderate approach of time restricted eating,” says Taylor. “Start by cutting out nighttime eating and snacking and then start to limit your ‘eating window’ each day – such as only eating from 8 a.m. to 6 p.m.”

As you progress and monitor how you feel, you may choose to gradually increase your fasting window.

Speak with your doctor or a dietitian before starting IF, Taylor recommends, and proceed with caution and take it slow.

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