Intermittent fasting is a timed approach to eating. Before starting, a person can prepare by working out why they want to fast and the type of fast and meal plan that suits them best.

Intermittent fasting involves cycling between periods of eating and fasting. It does not specify which foods to eat or avoid but recommends a window in which to consume food.

Though fasting is generally safe for many people, it may not be appropriate for individuals with medical conditions. People can speak with a healthcare professional about whether intermittent fasting is right and safe for them.

This article offers tips on how to begin fasting, including identifying personal goals, planning meals, and establishing calorie needs.

A person who is intermittent fasting eating during their chosen period.-2Share on Pinterest
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Typically, a person who starts intermittent fasting has a goal in mind, such as:

A person’s ultimate goal can guide their choice of fasting method and help them determine how many calories and nutrients they need.

People may try multiple methods when fasting for health reasons. They should pick a plan that suits their preferences and they think they can stick to.

A few of the more popular types of fasting plans are:

  • periodic fasting
  • time-restricted eating
  • alternate-day fasting

Anyone with a medical condition should consult a healthcare professional before beginning any fasting method. Fasting is not a safe option for some people.

When deciding on a method, a person should remember that they do not need to eat a certain amount or type of food or avoid certain foods altogether. A person can eat what they want when following an intermittent fasting plan.

However, following a balanced diet during the eating periods may help people reach health and weight management goals.

Eating only foods that lack beneficial nutrients during eating periods may hinder health progress. Drinking enough water or other no-calorie beverages during fasting periods is also essential.

Below are some examples of intermittent fasting methods.

Periodic fasting

This structure involves fasting within specific periods, such as twice per week. Examples include the following:

  • Eat Stop Eat: Brad Pilon developed Eat Stop Eat, a fasting method that involves eating nothing for 24 hours twice a week on nonconsecutive days.
  • 5:2 method: A person on the 5:2 method eats 500 to 600 calories two days each week, on consecutive or nonconsecutive days, depending on the specific plan.

People who do not eat for a prolonged period may become very hungry. Eat Stop Eat, and other plans that involve not eating for a long time, may not be the easiest or most comfortable method for people unfamiliar with fasting.

A person should consult a doctor or registered dietitian before starting a fasting plan like this one.

Time-restricted eating

Plans such as the Warrior Diet and the 16:8 or 14:10 method are time-restricted eating plans. They involve consuming calories only during specific periods throughout the day.

  • Warrior Diet: Ori Hofmekler created the Warrior Diet, which entails eating very little for 20 hours each day. A person fasting this way consumes all their typical food intake in the remaining 4 hours.
  • 16:8 method: 16:8 intermittent fasting allows for a fast lasting 16 hours per day, with all foods eaten during the remaining 8 hours. People may choose to include nighttime hours in their fasting period.

The Warrior Diet is another more extreme fasting method. Eating a whole day’s worth of food in such a short time, as it recommends, may cause stomach discomfort.

As with Eat Stop Eat, a person new to fasting may wish to start with an easier method and should consult a doctor first.

Alternate-day fasting

Some people fast on alternate days with the aim of improving the following:

Some alternate-day fasting regimens add a third day of fasting each week. For the rest of the week, a person eats only the number of calories they burn during the day. Over time, this creates a calorie deficit that allows the person to lose weight if that is their goal.

People who take diabetes medications, such as sulfonylureas or insulin, which may cause hypoglycemia, must discuss fasting with a healthcare professional to avoid a serious low blood sugar event.

There are typically no inherent dietary restrictions when intermittent fasting, but this does not mean calories do not count.

People working with a doctor or dietitian to manage their weight may need to create a calorie deficit, which means consuming fewer calories than they use. People aiming to gain weight will need to consume more calories than they use.

A person can consult a healthcare professional or dietitian for guidance on how many calories they need. A professional can help people determine the best foods for them and find a healthy way to lose weight.

Learn how many calories a person needs.

A person interested in losing or gaining weight may find it helpful to plan what they are going to eat during the day or week.

Meal planning does not need to be overly restrictive. It considers calorie intake and incorporating proper nutrients into the diet. For example, the United States Department of Agriculture’s MyPlate Plan focuses on daily food group targets.

Meal planning offers the following potential benefits:

  • helping people stick to their calorie count
  • ensuring people have the necessary ingredients on hand for recipes, quick meals, and snacks
  • helping people save money by wasting less food

Not all calories are the same. Although many intermittent fasting methods do not limit the number of calories a person consumes during eating periods, it is essential to consider the nutritional value of the food.

In general, a person should aim to consume nutrient-dense foods, which are foods with a high number of nutrients per calorie.

People may not have to abandon less nutritious food entirely, but they should still practice moderation and focus on more nutritious options to gain the most benefits.

Read a list of nutrient-dense foods.

The effectiveness of intermittent fasting may depend on a person’s overall goals. Fasting may cause the following effects on a person’s body:

  • reduced insulin levels, making it easier for the body to use stored fat
  • lower levels of:
  • changes to the expression of certain genes, which may help the body protect itself from disease and promote longevity
  • activating autophagy, a process in which the body digests or recycles old or damaged cell components
  • increases human growth hormone levels, which can help the body use body fat and grow muscle

Intermittent fasting can be effective for weight management. According to a 2020 review of studies, the practice may be helpful for treating obesity, though more long-term studies are necessary.

A 2024 scoping review suggests that while both intermittent fasting and general calorie restriction helped people lose weight, people were more likely to stick to intermittent fasting plans.

Some people may also find it challenging to stick to a fasting routine if they want to join in with social eating occasions and these gatherings occur on a fasting day or outside their chosen eating window.

According to a 2023 cross-sectional study surveying 147 people in a Saudi population practicing intermittent fasting, the most common side effects included:

Side effects may vary in severity from person to person. However, the study authors highlight that the side effects of intermittent fasting did not typically require medical treatment.

Intermittent fasting may also cause dehydration or malnutrition if a person does not consume enough water or a good balance of nutrients during their eating periods.

Working with a healthcare professional can help a person get adequate nutrients when trying intermittent fasting.

Learn more about dehydration.

Risks for people with certain conditions

People with medical conditions should consult their doctor before beginning any fasting program.

A 2023 article suggests that the following people should not participate in intermittent fasting:

  • pregnant people
  • people who are lactating
  • children
  • older adults
  • people with or at risk of eating disorders

People can speak with a healthcare professional before starting intermittent fasting to ensure it is safe to try.

Intermittent fasting may cause side effects such as dizziness and lethargy. These may make it more challenging to exercise for some people.

A 2019 review highlights mixed results from studies exploring the effect of intermittent fasting on athletic performance. The authors call for more research to determine the long-term effects.

According to a 2024 systematic review and meta-analysis, combining intermittent fasting and exercise training may produce better changes in body composition.

However, the authors highlight that this combination was not necessarily better than performing either intermittent fasting or exercise training alone for improving cardiometabolic health markers.

People who plan to combine exercise with intermittent fasting can work with a healthcare professional to ensure they get all the nutrients they require during their eating periods.

Below are some common questions about intermittent fasting.

How should a beginner start intermittent fasting?

Someone new to intermittent fasting should consider their goals and the most appropriate plan. Beginners may find plans with long fasting periods, such as the Eat Stop Eat plan or Warrior plan, difficult to stick to.

Fasting plans with less extreme fasting periods, such as the 5:2 fasting plan, may be more comfortable for beginners.

What is the best time to start intermittent fasting?

Many fasting plans do not specify a specific time to start fasting. However, the most suitable time may depend on the plan a person chooses and their schedule.

For example, people trying time-restricted eating may wish to include nighttime periods in their fasting time.

Intermittent fasting involves restricting calories in certain periods. The amount of time a person fasts for and the severity of calorie restriction may vary depending on the plan they choose.

Although a person does not need to exclude certain foods from their diet while fasting, they should aim to eat a balanced diet rich in protein, fiber, fruits, and vegetables. It is also important to drink plenty of low calorie or no calorie fluids.

Some people may experience side effects, such as headache or lethargy, while fasting. People can speak with a healthcare professional to ensure fasting is a safe and potentially effective option for them.