Side Effects of Fasting for Three Days

Consuming no food for three days, also known as a short-term fast, involves drinking only water or juice, but refraining from all other foods. You might choose a short-term fast of three days as part of a detoxification diet or to lose weight rapidly. However, no food for three days might result in unpleasant and unhealthy side effects. Consult a dietitian or your health care practitioner for advice before embarking on a fast for any length of time.

Fatigued young woman laying on a bed. (Image: Kane Skennar/Photodisc/Getty Images)

The Basics

Proponents of a short-term fast as all or part of a detox diet say it helps purify your body by removing environmental toxins and allowing your internal organs to heal from the stresses they encounter in your everyday life. As a weight-loss tactic, no food for three days drastically limits your calorie consumption so your body must rely on energy stores to fuel your activities. Ancient cultures relied on fasting as a means of soul purification. While removing food from your diet for three days results in physical and mental side effects, your perception of these effects might depend on your reasons for fasting.

Physical Effects

Physical effects of a short-term fast might include hunger, headache, fatigue and dizziness as your blood sugar levels become depleted. You might start to burn body fat for fuel as you run out of glycogen, the starch your body stores in your muscles and liver. However, you might also begin to lose muscle mass as your body turns to your muscle protein as an additional source of energy and to maintain its need for enzymes, hormones and immune cells. While you might lose weight during these three days of fasting, the bulk of your weight loss is due to loss of water and lean muscle tissue, says the American Council on Exercise.

Mental Effects

In addition to the physical fatigue you might feel during a three-day fast, you might also experience mental fatigue, along with food cravings and irritability. On the other hand, you might experience the side effects of fasting as an uplifting feeling that leaves you with more focus and energy than you had before. However, these positive reactions might simply be due to believing you are helping your body, explains dietitian Katherine Zeratsky of the Mayo Clinic.


A three-day fast might be dangerous to your health if you are already malnourished. It might also increase your risk of a gout attack if you are prone to this condition. A fast of any length is contraindicated if you are pregnant or nursing. Furthermore, fasting for the purpose of detoxification is unproven and might be unnecessary, as your liver and kidneys serve this physiological function in your body.

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