Pros and Cons of 5 Intermittent Fasting Methods

Intermittent fasting is an eating pattern during which you refrain from consuming any calories for an extended period of time. Usually, this period lasts between 12 and 40 hours (1).

Water, coffee, and other calorie-free beverages are allowed during the fast, but no solid foods or calorie-containing drinks are permitted.

For example, if you finish dinner at 7 p.m. Monday and don’t eat again until 7 p.m. Tuesday, you’ve completed a 24-hour fast. Some people choose to fast from breakfast to breakfast or lunch to lunch. But which time frame works best depends on the individual.

A full 24-hour fast every other day can seem extreme and may be difficult for many people to maintain, so it’s usually not recommended for beginners. However, you don’t have to go all-in right away, and many intermittent fasting routines start with shorter fasting periods.

Here are 5 of the most popular eating patterns for adding intermittent fasting to your diet:

• Time-restricted eating. Involves fasting every day for 12 hours or longer and eating in the remaining hours. A popular example is the 16/8 method. It features a daily 16-hour fast and an 8-hour eating window wherein you can fit in 2, 3, or more meals.
• The 5:2 diet. The 5:2 diet involves eating as you normally do 5 days of the week and restricting your calorie intake to 500–600 on the remaining 2 days.
• Eat Stop Eat. Eat Stop Eat involves a 24-hour fast once or twice per week.
• Alternate-day fasting. With alternate-day fasting, the goal is to fast every other day.
• The Warrior Diet. The Warrior Diet was among the first popular diets to include a form of intermittent fasting. It involves eating small amounts of raw fruits and vegetables during the day and eating one large meal at night.

SUMMARY

Intermittent fasting is a dietary routine that regularly alternates between periods of eating and fasting. There are many different methods of doing so, with many requiring you to fast for 12–40 hours at a time.

Researchers have already linked numerous health benefits with intermittent fasting and continue to examine them.

Plus, for some people, intermittent fasting fits well into their model of a healthy and sustainable long-term diet.

If you’re wondering if intermittent fasting could be right for you, here are a few benefits that might pique your interest.

1. Might support weight loss and improve metabolic health

Two main reasons why people try intermittent fasting are to manage their weight and metabolic health. Metabolic health is a marker of how well the body processes, or metabolizes, energy. It’s often measured by blood pressure, blood sugar, and blood fat levels (2, 3, 4, 5).

Fasting or abstaining from food can create a calorie deficit, meaning that your body has fewer calories than it needs to maintain its current weight. That’s why diets that rely on calorie restriction, like fasting, are the hallmark of most weight loss diets.

Research shows that some types of intermittent fasting can be as effective for weight loss — though not necessarily more effective — as other diets that also rely on limiting your daily calorie intake (6, 7, 8, 9).

Time-restricted eating routines similar to the 16/8 method are one type of intermittent fasting that has been linked directly with weight loss. Alternate-day fasting and the 5:2 diet may also be effective (10, 11, 12, 13).

Besides naturally eliminating your calorie intake during the fasting period, intermittent fasting may support weight loss by regulating your appetite to increase feelings of fullness while suppressing feelings of hunger (14, 15, 16).

The eating pattern has also been linked with other improvements in health, such as:

• lowering blood pressure (15, 17, 18, 19)
• improving blood sugar (4, 11, 15, 20)
• repairing damaged cells (21)
• protecting brain health (22, 23, 24)

2. Can be a sustainable lifestyle change

Intermittent fasting might sound complicated and intimidating, but it can be simple at times. In fact, you might even find that fasting helps simplify your day since you need to plan fewer meals.

What’s more, it doesn’t typically require calorie counting, watching your macros, eating certain foods that you might not be used to eating, or eliminating certain foods that you otherwise enjoy.

For example, having an early dinner followed by a late breakfast the next day is one way to fast intermittently. If you finish your last meal at 8 p.m. and don’t eat until noon the next day, you’ve technically fasted for 16 hours.

For people who get hungry in the morning and like to eat breakfast, or for those who can’t eat until later in the evening due to work schedules and other obligations, this method may be hard to get used to.

However, other people instinctively eat this way already. They may be more prone to trying out an intermittent fasting eating pattern.

3. Works well with a nutritious, whole foods diet

Because intermittent fasting is focused more on when rather than what you eat, it’s generally easy to implement in conjunction with your current diet.

You won’t necessarily need to buy any special foods or diverge much from what you typically eat.

If you’re already content with the state of your current diet but looking for other ways to continue boosting your overall health, fasting might be something you want to explore.

For example, intermittent fasting might work particularly well for someone who wants to pair it with a resistance training program and a high protein diet (25).

Still, this isn’t meant to imply that what you eat doesn’t matter. There’s no doubt that you’ll reap the most benefits from intermittent fasting by eating a variety of nutritious foods and limiting ultra-processed foods during your eating window.

SUMMARY

Intermittent fasting is often used to manage weight and metabolic health. The eating routine might help lower blood pressure, blood sugar, and blood fat levels. For some people, it also works as part of a healthy long-term diet pattern.

Intermittent fasting is one way to regulate your calorie intake and work toward improving your metabolic health.

Though the eating pattern can certainly be part of a healthy diet, it will likely take some adjusting to in the beginning. Plus, simply put, intermittent fasting is not right for everyone.

Here are a few downsides you could encounter when first trying intermittent fasting.

1. Might go against your intuition

Intermittent fasting requires discipline, restraint, and planning ahead.

For some people, using those tactics to keep your calorie intake within a designated time frame is no problem, but for others, it might feel unnatural at first. This may be especially true if you’re used to relying on your intuition to decide when to eat.

Further, if you prefer not to follow a strict schedule, you might find intermittent fasting frustrating.

What’s more, if your schedule tends to vary from day to day because of work, family, or other obligations, keeping your calorie intake to a designated time frame could be challenging.

2. You’ll likely feel hungry

Even an 8- or 12-hour fast might feel like a long time when you’re not used to fasting.

You may go to bed hungry several times per week. That may naturally feel unpleasant and unsustainable in the long term (26).

Plus, at times, it might be necessary to override your natural hunger and fullness cues in order to not break your fast earlier than planned.

This doesn’t mean that fasting isn’t a schedule you can get used to. Once you’ve adjusted to intermittent fasting, you might even find it makes you feel less hungry (14, 15).

Many people adjust to the routine, and some even find they enjoy it after a few months. Yet, hunger and frustration are certainly something to expect and be aware of initially.

3. The side effects could affect your mood

When you first try intermittent fasting, one of the first things you may notice — aside from feeling more hungry — is ups and downs in your mood.

This is understandable. Besides initially increasing hunger levels, fasting can have side effects, including headaches, constipation, fatigue, sleep disturbances, and more (15, 27, 28, 29).

What’s more, irritability and anxiety are classic symptoms of low blood sugar levels. This is a common bodily response to fasting or restricting calories (30, 31, 32).

Still, like hunger, your emotional well-being may be another side effect of intermittent fasting that will improve with time and practice (15).

Once you’ve had time to adjust, intermittent fasting may even bring you a sense of achievement or pride (32).

SUMMARY

Especially in the beginning, intermittent fasting can have side effects like hunger, headaches, and fatigue. The combination of low blood sugar levels from fasting and the stress of adjusting to a new routine could affect your mood and mental health, too.

What are the basic rules of intermittent fasting?

Intermittent fasting is when you don’t eat any calories for a specific length of time, usually between 12 and 40 hours.

Why is 16 hours the magic number for fasting?

The 16/8 method features a daily 16-hour fast and an 8-hour eating window wherein you can fit in 2, 3, or more meals. This method has been linked to weight loss, although there is not enough evidence to show is is better than any other method for losing weight.

Is 12 hours considered intermittent fasting?

Many people fast for a 12-hour period, say, from 8.00 PM one day to 8.00 AM the next. This type of fast can help you avoid late night snacking.

How many hours should you fast to do intermittent fasting?

A fast can last from 12 to 40 or more hours. It is best to start with 12 hours and only take on a longer fast under medical supervision or after speaking with a doctor.

Intermittent fasting is a weight loss tool that works for some people, but not everyone.

It’s not recommended for individuals who once had or currently have an eating disorder. It may also be unsuitable for children, people with underlying health conditions, and people who are pregnant or breastfeeding.

If you decide to try intermittent fasting, remember that just like with any eating pattern, diet quality is key.

To gain the most from intermittent fasting, be sure to eat a variety of nutrient-dense whole foods during your eating window and limit ultra-processed foods.

Furthermore, before embarking on an intermittent fast, be sure to consult a trained healthcare professional to ensure that it’s safe for you to do so.