Should You Avoid Fasting?

While fasting is getting great press for its numerous health benefits, it’s not for everyone. There are a variety of reasons for certain people to avoid fasting, either short or longterm, to stay in optimum health. Here are just a few groups who should likely avoid fasting or work closely with a doctor to devise a specialized plan:

Pregnant or Nursing Mothers

Pregnant women need to be sure to take in an appropriate number of calories and nutrients during gestation. While research varies on the outcomes of fasting during pregnancies, there is some evidence that fasting while pregnant may increase the likelihood of preterm labor and result in babies with lower birth weight or shorter stature. Most significantly is the finding that when a pregnant mother fasts, fetal breathing drops, though it resolves once the mother eats again.

When fasting, pregnant and nursing mothers both have a higher risk for hypoglycemia due to lower blood glucose levels and are at risk of dehydration, which can have an impact on the fetus’s amniotic fluid levels and breast milk production. Therefore, it is generally not recommended.

Eating Disorders

For people struggling with eating disorders such as anorexia nervosa or bulimia, fasting is not recommended, as it can easily play into disordered eating patterns, such as starving or vomiting up meals. Some signs that fasting is becoming disordered eating include:

· Anxiety about eating

· Extreme fatigue (often from lack of nutrition)

· Dramatic changes in hormones or menstrual cycle

To find out if you are at risk of an eating disorder, the National Eating Disorders Association offers this self-assessment tool.

Type 1 Diabetes

Fasting is not recommended in patients whose type 1 diabetes is poorly controlled, including those who have a history of severe hypoglycemia and/or diabetic ketoacidosis; anyone who has additional conditions such as angina, hypertension, or kidney problems; those who are not properly taking their medication; who perform intense physical activity; or are elderly with diabetes. With the permission and observation of a physician, some people with Type 1 diabetes, which is an autoimmune disease, may be able to fast, however, that comes with a huge caveat, and should not be undertaken without medical permission first because fasting can lead to hypoglycemia.

This meta-analysis shows that fasting as a type 1 diabetic can come with some risks, such as hypoglycemia and hyperglycemia. However, it also suggests that the type of insulin therapy used while fasting, along with the supervision of a healthcare practitioner who can adjust the insulin therapy, can mitigate the risk of these adverse events.

Type 2 Diabetes

Under the supervision of a healthcare provider, fasting for people with type 2 diabetes may be safe so long as the diabetes is under control. One study found that a seven day liquid fast of only 300 calories per day proved safe for those with type 2 diabetes. However, another study on people with type 2 diabetes showed that the chance of low blood sugar incidents doubled on fasting days versus non-fasting days, which could lead to hypoglycemic events. So, as long as you are under the care of a medical practitioner who is knowledgeable about fasting, it may be an option for you. Fasting is also shown to be effective for people who have pre-diabetes, but so is simply reducing carbohydrate intake and adding more exercise.

The Elderly

While there are no hard guidelines about the safety of fasting as it relates to age, medical professionals warn that elderly folks with any chronic health conditions, especially diabetes, kidney problems, or heart disease, should not fast as it could be dangerous to their health. If an older adult is in good health and not taking any medication, fasting under the supervision of a doctor may be okay, however, older adults are at greater risk of dehydration, and must be careful to replenish water and electrolytes.


Growing bodies need good nutrition as consistently as possible. Therefore, fasting is not recommended for kids and teens, who undergo rapid growth and are still developing. For youths that need to lose weight, caloric restriction and reduction of carbohydrates may be just as effective.


The first rule of fasting is to make sure you consult with your doctor before you begin. This is especially important if you take any medications. Every medication is different. One of the biggest concerns is that many medications need to be taken with food and at a certain time of day, which may interfere with a fasting window, or putting off a medication to a later eating window could impair the medication’s efficacy. Additionally, glucose-lowering medications such as metformin, berberine, and sitagliptin, as well as exogenous insulin should be closely monitored and adjusted during a fast due to their glucose lowering effects. Depending on the type and the duration of the fast, some medications need to be held until the fast is over or moved to a different time of the day or week.

Fasting can also lead to dehydration if one is not careful, which can reduce blood pressure, impair the body’s electrolyte balance, have a negative effect on heart function, and potentially cause kidney damage. If you are taking a medication for blood pressure or kidney issues, this could be very dangerous.

Current Medical Conditions

Anyone with a medical condition should consult their physician before undertaking a fast. Fasting can cause changes in blood sugar, hormones, and blood pressure, which can affect numerous health conditions.

You should also consider situational and external factors when considering a fast including, but not limited to: periods of high stress, travel — especially changing time zones, which can interrupt your circadian rhythm — or high-intensity and prolonged exercise. Each of these situations can put you at a higher risk for hypoglycemia, as well as electrolyte and fluid imbalances. When choosing to fast, these situations need to be considered and a conversation with your doctor or supervising healthcare practitioner is needed.

In Conclusion…

Ultimately, while fasting may sound great, be safe. Consider your specific health conditions and work with your doctor to advise you on the best plan. There are many different fasting protocols — from multiple day, water-only fasts to time-restricted feeding — that support a range of goals and have varying degrees of safety for certain populations. So, when you’re deciding if, when, or how to fast, always consult with a medical professional. Your health will thank you.


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