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Fasting involves limiting food intake for a period of time. Intermittent fasting, including "time-restricted feeding", has become a common dieting strategy.

Intermittent fasting involves eating very little for a short period of time. This might mean that fasting occurs for 12-16 hours each day, for 1-2 days per week, or every other day. Normal eating takes place during the rest of the day or week. This approach is sometimes used as a dieting strategy because it can reduce the total amount of calories that a person eats over time. This may lead to weight loss and other health benefits.

People use intermittent fasting for metabolic syndrome and obesity. It is also used for athletic performance, aging, diabetes, heart disease, epilepsy, and other conditions, but there is no good scientific evidence to support these uses.

Is It Effective?

Effectiveness header

Natural Medicines rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.

Possibly effective
  • A grouping of symptoms that increase the risk of diabetes, heart disease, and stroke (metabolic syndrome). Intermittent fasting for 4-12 weeks seems to improve body weight and waist circumference in people with metabolic syndrome. But it's not clear if it helps to improve blood pressure, blood sugar, or cholesterol levels.
  • Obesity. Intermittent fasting seems to help with weight loss in people who are overweight or obese. But it's not clear if it's more helpful than other diets that also reduce calories.

There is interest in using fasting for a number of other purposes, but there isn't enough reliable information to say whether it might be helpful.

Is it Safe?


Intermittent fasting is possibly safe when used appropriately, short-term. It has been practiced for up to 12 months with no serious side effects. The safety of intermittent fasting when used longer than 12 months is unclear.

Complete, water-only fasting is possibly safe for up to 22 days under medical supervision. But complete fasting is likely unsafe when done without medical supervision. This may lead to serious health issues and even death.

Special Precautions & Warnings:

Pregnancy and breast-feeding: There isn't enough reliable information to know if fasting is safe to use when pregnant or breast-feeding. Stay on the safe side and avoid fasting.

Drug interactions


Interaction Rating=Moderate Be cautious with this combination.

Fasting can lower blood sugar. Insulin is also used to lower blood sugar. Fasting while using insulin might cause your blood sugar to be too low. Monitor your blood sugar closely. The dose of your insulin might need to be changed.

Medications for diabetes (Antidiabetes drugs)

Interaction Rating=Moderate Be cautious with this combination.

Fasting might lower blood sugar levels. Fasting while taking diabetes medications might cause blood sugar to drop too low. Monitor your blood sugar closely.

Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)

Interaction Rating=Moderate Be cautious with this combination.

Fasting might slow blood clotting. Fasting while taking medications that also slow blood clotting might increase the risk of bruising and bleeding.

Warfarin (Coumadin)

Interaction Rating=Major Do not take this combination.

Warfarin is used to slow blood clotting. Fasting while taking warfarin might increase the effects of warfarin. This might increase the chance of bleeding. Be sure to have your blood checked regularly. The dose of your warfarin might need to be changed.

Herb interactions

There are no known interactions with herbs and supplements.

Food interactions

There are no known interactions with foods.


Fasting practices vary. The most common types of fasting are called "intermittent fasting". These include alternate-day fasting, periodic fasting, time-restricted feeding, and religious fasts. Some people also follow longer fasts under medical supervision.

Alternate-day fasting involves alternating between fasting for one day then eating food as desired the next day. Periodic fasting involves fasting for 1-6 days per week then eating food as desired for the remainder of the week. Usually, fasting is for 2 days each week. Time-restricted feeding involves eating only during a certain time period each day. Religious fasts such as the Ramadan fast involve fasting from sunrise to sunset for one month.

Other names

5:2 Diet, 5:2 Intermittent Diet, Alternate-Day Fasting, Alternate-Day Modified Fasting, Caloric Restriction, Chrononutrition, Energy Restriction, IER, Intermittent Energy Restriction, Intermittent Fasting, Intermittent Severe Energy Restriction, Modified Alternate-Day Fasting, Periodic Fasting, Ramadan Intermittent Fasting, Time-Restricted Eating, Time-Restricted Feeding, Therapeutic Fasting, Total Caloric Desistance, Water-Only Fasting, Zero Calorie Diet.


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