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What is Intermittent Fasting and How does it Work?

Published : February 13, 2024 6 mins read Updated On : Mar 22, 2024

Eating in cycles between times when you eat and when you fast are known as intermittent fasting (IF). Several research and periodic studies on intermittent fasting have found that intermittent fasting has a positive effect on blood sugar, cholesterol, and blood pressure levels. Additionally, some studies suggest it may have positive effects on brain health and longevity. Intermittent fasting primarily focuses on when to eat rather than what to eat. There are several methods of intermittent fasting, and the effectiveness may vary from person to person.

What is Intermittent Fasting and How does it Work?

What is Intermittent Fasting

Intermittent fasting is an eating pattern that alternates between periods of eating and fasting. It doesn't prescribe specific foods but focuses on when to eat. Common methods include the 16/8 method (16 hours fasting, 8 hours eating) or the 5:2 method (eating normally for five days, then consuming fewer calories on two non-consecutive days) (1).

Benefits of Intermittent Fasting

Weight Loss: Restricting eating windows can lead to calorie reduction, aiding weight loss.

Improves Insulin Sensitivity: Helps regulate blood sugar levels, reducing the risk of type 2 diabetes (2).

Enhance metabolic rate: May support better cholesterol levels and blood pressure.

Reduce Inflammation: May decrease inflammation markers in the body.

Here are some common approaches to intermittent fasting:

1. Time-Restricted Eating (TRE):

Time-restricted feeding (TRF), also known as time-restricted eating (TRE), is a form of intermittent fasting that involves limiting the daily eating period typically ranging from 12 to 20 hours, followed by a designated eating window, while maintaining a consistent daily fasting period. The primary focus of time-restricted fasting is on when you eat rather than what you eat.

Example: 16/8 method involves a 16-hour fast with an 8-hour eating window.

Foods to include: Focus on eating a well-balanced diet with whole grains, lean protein sources, healthy fats, seasonal fruits and vegetables and probiotic sources like curd, kefir or fermented foods.

2. Alternate-Day Fasting:

Alternate day fasting (ADF) is a form of intermittent fasting that involves alternating between days of regular eating and days of fasting or significantly reduced calorie intake. This eating pattern has gained attention for its potential benefits related to weight loss and metabolic health. Alternates between days of regular eating and days of fasting or consuming very few calories.

Example: Eat normally on one day and either fast or consume around 500 calories on the next day.

Foods to include: On regular eating day include lean sources of protein like chicken, fish, eggs, legumes (beans, lentil), whole grain, healthy fats and seasonal fruits and vegetables. Staying hydrated is crucial on both days. On fasting days, it's crucial to consume foods that are low in calories but still provide essential nutrients to support your body like low calories vegetables, lean sources of protein, broth-based soups and high fiber foods like chia seeds, flax seeds etc to keep yourself full.

3. 5:2 Diet: 

5:2 diet involves eating normally for five days of the week and restricting calorie intake to around 500-600 calories on two non-consecutive days.

Example: Eat normally on Monday, Wednesday, Friday, and Sunday; restrict calories on Tuesday and Thursday.

Foods to include: Focus on eating a well-balanced diet with whole grains, lean protein sources, healthy fats, seasonal fruits and vegetables and probiotic sources like curd, kefir or fermented foods.

4. Warrior Diet:

The Warrior diet typically consists of eating small amounts of raw fruits and vegetables during the day and having one large meal at night within a 4-hour eating window.

Example: Fast during the day, eat a large meal in the evening.

Foods to include: For small raw snacks throughout the day include fruits, vegetables, nuts, seed and hydrating beverages like coconut water, plain water, herbal teas. For the main meal, eat a balanced meal with lean protein source, whole grain and healthy fat like avocado, olive oil etc.

Who should do intermittent fasting?

  • Healthy adults
  • Individuals looking for weight management
  • Individuals looking to boost metabolic health
  • Individuals with a flexible lifestyle

Who should not do intermittent fasting?

  • Individuals with eating disorder
  • Pregnant and breastfeeding mother
  • Children and adolescent
  • Individuals with metabolic disorder should always consult their healthcare provider before starting.
  • Individuals with any chronic health condition

How Intermittent Fasting Works?

Insulin Sensitivity: During fasting periods, insulin levels drop. Improved insulin sensitivity can enhance the body's ability to use stored fat for energy.

Cellular Repair and Autophagy: Fasting triggers autophagy, a process in which cells remove damaged components. This may contribute to cellular repair and maintenance. (3)

Hormonal Changes: Fasting can lead to changes in hormone levels, including an increase in norepinephrine and human growth hormone (HGH), which play roles in fat metabolism and muscle preservation.

Caloric Restriction: Intermittent fasting often results in a natural reduction in calorie intake, contributing to weight loss. However, it's essential not to overcompensate by overeating while eating windows.

Metabolic Switch to Ketosis: In the absence of food, especially carbohydrates, the body shifts its primary energy source from glucose to stored fat. This metabolic switch leads to the production of ketones, which can be used by the body and the brain for energy.

Circadian Rhythm Alignment: Aligning eating patterns with the body's natural circadian rhythm may influence overall health. Eating during the daylight hours and fasting during the night can support the body's natural physiological processes.

Metabolic Rate: Some studies suggest that intermittent fasting may help maintain metabolic rate during weight loss, preventing the slowdown often associated with continuous calorie restriction.

Satiety and Hunger Hormones: Fasting may influence hormones related to hunger and satiety, potentially helping individuals better regulate their food intake.

Intermittent fasting can be an effective approach for some people, but it's essential to find a method that fits your lifestyle and health needs. It's crucial to prioritize nutrient-dense foods and maintain a balanced diet during eating windows. Some people may experience an adjustment period as the body adapts to a new eating pattern. Always consult with a healthcare professional or registered dietitian before making significant changes to your eating patterns.


Is it better to fast for 12 or 16 hours?

Intermittent fasting is highly individual, and what works for one person may not work as well for another. It might be beneficial to experiment with both 12-hour and 16-hour fasting windows, observe how your body responds, and choose the approach that feels sustainable and aligns with your overall well-being.

What is the best time for intermittent fasting?

The best time for intermittent fasting largely depends on individual preferences, daily schedules, and lifestyle factors. Make your choice considering factors like your daily routine, body needs and choose a time and routine in which you can be consistent.

Can I lose 10kg in a month with intermittent fasting?

Yes, you can lose 10 kg with intermittent fasting. But the results greatly depend on the diet pattern, lifestyle, consistency and exercise regime etc.

Does sleeping count as fasting?

Yes, sleeping does count as a fasting period. When you are asleep, your body is in a natural fasting state, as you typically do not consume food during this time. The period between your last meal of the day and your first meal the next day is often referred to as the overnight or fasting period.

Reference link-
Collier R. Intermittent fasting: the science of going without. CMAJ. 2013 Jun 11;185(9):E363-4. doi: 10.1503/cmaj.109-4451. Epub 2013 Apr 8. PMID: 23569168; PMCID: PMC3680567.

Patterson RE, Laughlin GA, LaCroix AZ, Hartman SJ, Natarajan L, Senger CM, Martínez ME, Villaseñor A, Sears DD, Marinac CR, Gallo LC. Intermittent Fasting and Human Metabolic Health. J Acad Nutr Diet. 2015 Aug;115(8):1203-12. doi: 10.1016/j.jand.2015.02.018. Epub 2015 Apr 6. PMID: 25857868; PMCID: PMC4516560.

Soumil Vartak
Health and Fitness enthusiast

Soumil is really passionate about health and fitness. He provides great insight on various trends about health and fitness. By writing about these topics he try to provide key insight on diet and e... Read More


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