Intermittent fasting (IF) is a term for an eating pattern that cycle between periods of fasting and eating. It is currently very popular in the health and fitness community and can be used along with calorie restriction for weight loss.
One form of intermittent fasting, alternate day fasting (ADF), involves a 24-hour fast followed by a 24-hour non-fasting period. This is sometimes referred to as every other day fasting or every other day feeding. Alternate-day calorie restriction may prolong life span.
Another form involves eating for limited times every day. One might fast for 14, 16 to 23 hours and then eat healthily. Choosing 14 or 16 hours actually allows eating twice per day, such as eating at 12:00 noon and again about 7:00 PM of an evening finishing at 8:00 PM. The time until the next noonday meal can be mitigated by sleeping 8 or 9 hours during that 16 hours fast. One can choose fasting 23 hours and one meal per day.
These are the most popular methods. The 16/8 Method: Also called the Leangains protocol, it involves skipping breakfast and restricting your daily eating period to 8 hours, for example from 1 pm to 9 pm. Then you “fast” for 16 hours in between.
Eat-Stop-Eat: This involves fasting for 24 hours, once or twice a week, for example by not eating from dinner one day until dinner the next day and the 5:2 Diet: On two non-consecutive days of the week, only eat 500-600 calories. Eat normally the other 5 days.
By making you eat fewer calories, all of these methods should make you lose weight as long as you don’t compensate by eating much more during the eating periods.
In some contexts, fasting allows the consumption of a limited amount of low-calorie beverages such as coffee or tea. Modified fasting involves limiting caloric intake (e.g., 20% of normal) on fasting days rather than none at all. A study suggests that this regimen may retain most of the benefits of intermittent fasting.
More generally, forms may choose to specify various ratios of fasting to non-fasting periods. The BBC2 Horizon documentary Eat, Fast and Live Longer, covered people who committed to fasting two non-consecutive days per week. Known as the 5:2 diet, people consumed 400–500 calories (women) or 500–600 calories (men) during the days of fasting. During feed days, the diet was regular.
A 2014 review described that studies done in animal models have shown fasting improves indicators of health such as blood pressure, insulin sensitivity, and inflammation likely through adaptive cellular responses to better handle stress. These findings suggest intermittent fasting has the potential to improve health and reduce the risk of chronic diseases, however this has not been reproduced in long term human studies. The review also concluded that intermittent fasting has not been studied in children, the elderly, or the underweight, and could be harmful in this population.
Intermittent fasting is certainly not for everyone. If you are underweight, or have a history of eating disorders or medical condition then you should not do intermittent fasting without consulting with a health professional first. In these cases, it can be downright harmful.
It is just one of many lifestyle strategies that can improve your health. Eating real food, exercising and taking care of your sleep are still the most important factors to focus on. If you don’t like the idea of fasting, then you can safely ignore all of this. Just continue to do what works for you. At the end of the day, there is no one-size-fits-all solution in nutrition.
The best diet for you is the one you can stick to in the long run.
