Although fasting for short periods is generally considered safe, the following populations shouldn’t attempt to fast without consulting a medical professional:
- People with a medical condition like heart disease or type 2 diabetes
- Women who are trying to conceive
- Women who are pregnant or breastfeeding
- People who are underweight
- Those who have experienced an eating disorder
- People who have problems with blood sugar regulation
- People with low blood pressure
- Those who are taking prescription medications
- Woman with a history of amenorrhea
- Older adults
SUMMARY While fasting can be healthy for many people, you should speak to your doctor first if you have certain medical conditions or are pregnant, breastfeeding or trying to conceive. Fasting is not recommended for people who have had an eating disorder
In addition, intermittent fasting isn't safe for those with eating disorders, since it could encourage both binge eating and anorexic behavior. It's also not safe for women who are pregnant. And, anyone who's been diagnosed with diabetes and/or heart disease should talk with their doctor before trying the diet, since it may not be the best choice for people with those conditions.
Finally, fasting can be extremely uncomfortable. People who fast often complain of headaches, fatigue, and general malaise. They also may feel light-headed. The fast diet can be difficult to stick with (and potentially unsafe for some people) because of this.
Some people fast as a way to lose weight. Others fast to try to detox their bodies, or for religious reasons.
If your goal is to detox your body, you should know that your body naturally detoxes itself.
Fasting diets aren't all the same. Some allow only liquids like water, juice, or tea. Others cut calories drastically, but don't completely ban food. And on some plans, you fast every other day.
Why Fasting for Weight Loss Can Backfire
When you eat less than you need and you lose weight, your body goes into a starvation mode. To save energy, your metabolism slows down.
When you're done fasting and you go back to your usual diet, you may regain the weight you lost, and then some.
On a fast, your body adjusts by curbing your appetite, so you will feel less hungry at first. But once you have stopped fasting, your appetite revs back up. You may feel hungrier and be more likely to overeat.
Fasting every other day has similar results. It helps people lose weight, but not for long.
In one study, people who fasted every other day shed weight, even when they ate all they wanted on days when they weren't fasting. But the weight loss didn't last over time.
Is Fasting Safe?
Fasting for a few days probably won't hurt most people who are healthy, provided they don't get dehydrated. But fasting for long periods of time is bad for you.
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. Fasting too long can be life threatening.
Before you go on a new diet, particularly one that involves fasting, ask your doctor if it's a good choice for you. You can also ask your doctor for a referral to a registered dietitian, who can show you how to design a healthy eating plan.