The health risks of intermittent fasting: It's not for everyone

Intermittent fasting is one of the most buzzed-about diets -- but should you try it?

Mercey Livingston CNET Contributor
Mercey Livingston is a health and wellness writer and certified Integrative Nutrition Health Coach. She's written about fitness and wellness for Well+Good, Women's Health, Business Insider, and Prevention.com among others. When not writing, she enjoys reading and trying out workout classes all over New York City.
Mercey Livingston
4 min read

Intermittent fasting is a popular health trend -- but is it safe for everyone?

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If there's a "golden child" of the wellness world from the last several years, it's intermittent fasting. The trend quickly took hold of the wellness community, and everyone from doctors to bloggers and fitness trainers began to talk about the seemingly miraculous effects it can have on health. 

Those effects include its potential to help people lose weight, decrease risk for cancer and disease and even improve longevity, according to a study in the New England Journal of Medicine.

With all of these benefits and promising research, it's hard to think that intermittent fasting wouldn't be worth the challenge of restricting food for periods of time. But some experts and researchers have questioned whether the benefits of fasting diets and intermittent fasting are worth the potential problems and challenges of maintaining a fasting diet. 

Intermittent fasting involves avoiding eating and snacking for certain periods of time (for some that's hours, and others a day or more) which makes insulin levels go down, requiring your body to use the energy stored in the fat cells for fuel. In addition to burning fat, there are animal studies and some human studies that show fasting can help lower blood sugar, quiet inflammation and improve other health issues. 

But as promising as the research is, it's important to keep in mind that a lot of it has been done on rats, which limits what we really know about what it can do for humans. According to Harvard Health, much of the research done on fasting in humans are shorter studies with small groups of people, so the results of those studies might not apply to most people. And there's not much research on what the potential effects of doing intermittent fasting can have on your health in the long term.

The safety and potential challenges of intermittent fasting varies based on each individual and health factors including age, gender, underlying health conditions, lifestyle and their overall health and well-being. Keep in mind that before you make drastic changes to your diet (like with IF or other diets), you should consult your doctor or health professional. Below are a few reasons you might want to reconsider if intermittent fasting is right for you and your goals. 


Fasting can interfere with female hormones, exacerbating issues like PMS or period pain.

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You have period pain, PMS or you're trying to get pregnant

Intermittent fasting requires you to restrict food for periods of time, which overtime, can make your body more sensitive to insulin. Insulin sensitivity is a good thing, it means your cells can use the energy (sugar) from the food you eat more efficiently, which ultimately helps lower your blood sugar. But for some, low blood sugar and hunger means more stress on the body. Going through long periods of fasting, resulting in low blood sugar and stress on the body, can mean bad news for your hormones and fertility.

"I don't recommend [intermittent fasting] if [women] have a lot of stress, aren't sleeping enough, are exercising a lot, are trying to get pregnant, have a history of disordered eating or have hormone imbalances or thyroid or adrenal issues...which pretty much excludes most women," says Melissa Groves Azarro, an integrative and functional medicine dietitian specializing in women's health and hormones.

Studies performed on young rats showed that fasting negatively affected reproductive health for male and female rats. "Women's hormones are super susceptible to perceived stress and scarcity, so intermittent fasting can worsen existing hormone imbalances. I do think it may be a useful tool in menopause, if sleep, stress and exercise are balanced," Azarro says.

You're looking for sustainable weight loss

While some people find intermittent fasting helps them succeed in their weight loss goals, some studies show that it is not much better (or about the same) as restricting calories in general. For many people, going for long periods without food is really difficult, and can cause them to overeat once the fast period is over. So if you end up eating the same or more calories than if you had just followed a calorie restriction plan with normal meal times, it may not be worth it if weight loss is your goal. 

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A recent study published in JAMA Internal Medicine showed that overweight adults who fasted for 16-hour windows didn't lose much more weight than the control group that did not fast, and most of the weight they did lose was from muscle loss.

"The benefits of fasting are really more around longevity and improving insulin sensitivity and some gut conditions. I don't view it as a tool for weight loss," Azarro says. If weight loss is your goal, you may be better off trying less restrictive or extreme weight loss programs, if it seems more realistic that you'll be able to stick to them.

You have certain medical conditions, like diabetes

There are certain groups of people who should not try intermittent fasting, especially without talking to their doctor first, due to real risks and dangers to their health. This includes people with diabetes, people who are on medication for blood pressure or heart disease, pregnant women and breastfeeding mothers. 

People who have blood sugar issues or are underweight could also be at risk. Anyone with preexisting medical conditions of any kind should reconsider fasting and consult their doctor before changing their diet.

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The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.