What is Intermittent fasting?

Intermittent fasting, also known as intermittent energy restriction, is an umbrella term for various meal timing schedules that cycle between voluntary fasting (or reduced calories intake) and non-fasting over a given period.

Three methods of intermittent fasting are alternate-day fasting, periodic fasting, and daily time-restricted feeding. Intermittent fasting may be similar to a calorie-restriction diet,and has been studied in the 21st century as a practice to possibly reduce the risk of diet-related diseases, such as metabolic syndrome. However, intermittent fasting has been criticised as a fad.

The science concerning intermittent fasting is contested. The American Heart Association (AHA) states that intermittent fasting may produce weight loss, reduce insulin resistance, and lower the risk of cardio-metabolic diseases, although its long-term sustainability is unknown.

The US National Institute on Aging states that there is insufficient evidence to recommend intermittent fasting and encourages speaking to one's healthcare provider about the benefits and risks before making any significant changes to one's eating pattern.A 2019 review concluded that intermittent fasting may help with obesity, insulin resistance, dyslipidemia, hypertension, and inflammation.

Forms of intermittent fasting exist in various religious practices, including Christianity, Hinduism, Islam, Jainism, and Buddhism.

Types

An alternate day fasting schedule, that alternates between usual eating (feast days) and fast days with reduced or no calories

Three methods of intermittent fasting are alternate-day fasting, periodic fasting, and time-restricted feeding:-

• Alternate-day fasting involves alternating between a 24-hour "fast day" when the person eats less than 25% of usual energy needs, followed by a 24-hour non-fasting "feast day" period. It is the strictest form of intermittent fasting because there are more days of fasting per week. There are two subtypes:-

• Complete alternate-day fasting (or total intermittent energy restriction), where no calories are consumed on fast days.
• Modified alternate-day fasting (or partial intermittent energy restriction) which allows the consumption of up to 25% of daily calorie needs on fasting days instead of complete fasting. This is akin to alternating days with normal eating and days with a very-low-calorie diet.

• Periodic fasting or whole-day fasting involves any period of consecutive fasting of more than 24 hours, such as the 5:2 diet where there are one or two fast days per week, to the more extreme version with several days or weeks of fasting.During the fasting days, consumption of approximately 500 to 700 calories, or about 25% of regular daily caloric intake, may be allowed instead of complete fasting.

• Time-restricted feeding involves eating only during a certain number of hours each day.Skipping a meal and the 16:8 diet (16 fasting hours cycled by 8 non-fasting hours) are examples. This schedule is thought to leverage the circadian rhythm.

The science concerning intermittent fasting is preliminary and uncertain due to an absence of studies on its long term effects.Preliminary evidence indicates that intermittent fasting may be effective for weight loss, may decrease insulin resistance and fasting insulin, and may improve cardiovascular and metabolic health, although the long term sustainability of these effects has not been studied.