One type of intermittent fasting, alternate day fasting known as (ADF), involves a 24-hour long fast that is followed by a 24-hour period of non-fasting. Alternate-day calorie restriction under basic research for whether it can prolong life. You can also choose fasting 23 hours with only one meal per day.
Some contexts, fasting allows the consumption of a minimal amount of low-calorie fluids such as coffee or tea. Modified fasting includes limiting calorie intake ( 20% of normal calorie intake) on fasting days opposed to none at all, retaining many of the benefits of intermittent fasting.
Generally, forms may choose to specify ratios of fasting opposed to non-fasting periods. The BBC Horizon documentary called Eat, Fast and Live Longer covered people who promised to fast two non-consecutive days per week. Called the 5:2 diet, people in total consumed 400–500 calories (women) or 500–600 calories (for men) during these days of fasting. However, during feed days, the diet was regular.