Fasting for a few days probably won’t hurt most people who are healthy, provided they don’t get dehydrated.
Your body needs vitamins, minerals, and other nutrients from food to stay healthy. If you don’t get enough, you can have symptoms such as fatigue, dizziness, constipation, dehydration, and not being able to tolerate cold temperatures.
Other people who should not fast include women who are pregnant or breastfeeding, anyone with a chronic disease, the elderly, and children.
Before you go on a new diet, particularly one that involves fasting, ask your doctor if it’s a good choice for you. Several studies show promise of intermittent fasting and several health benefits. Studies of intermittent fasting in humans with chronic disease have resulted in better control of their disease. However, these studies are done only over a period of months. It’s unclear if the benefits would remain for years if the diet is continued throughout life.
You can also ask your doctor for a referral to a registered dietitian, who can show you how to design a healthy eating plan.