Is Intermittent Fasting Bad for You?

Intermittent fasting requires you to restrict your eating to only specific time windows.

The thought behind this method is that by eating for fewer hours during the day or skipping one day and eating the next, you'll eat fewer calories overall. Still, you may wonder whether intermittent fasting is good for your health. 

Here's what you should know about how intermittent fasting works and some potential risks to consider if you're thinking of trying it.

Is Intermittent Fasting Bad for You?

Depending on how you fast, the weight loss method may be useful, at least in the short term. Some evidence suggests intermittent fasting is about as effective as daily calorie restriction without time restraints.

However, if you take fasting to the extreme, intermittent fasting may risk disordered eating, rebound eating that causes weight gain, and sleep disturbances. What's more, there isn't enough evidence showing whether intermittent fasting is a sustainable eating pattern.

Why People Try Intermittent Fasting for Weight Loss

There are many ways to do intermittent fasting. For example, some methods let you eat what you want one day and nothing on the next.

In contrast, others recommend restricting your eating to six-, eight-, or 12-hour windows and fasting in between. Another approach is to eat five days per week, then eat only 400 or 600 calories on two non-consecutive days.

Many people try intermittent fasting to maintain or reduce weight. However, a review published in 2019 in the New England Journal of Medicine found several health benefits beyond weight loss.

Specifically, intermittent fasting may reduce your risk of the following:

• Obesity
• Diabetes and high blood sugar
• Cardiovascular disease
• Certain cancers
• Some neurological disorders  
• Blood pressure
• Inflammation
• Heart rate  

That said, as of 2023, there isn't enough evidence to conclude whether fasting is practical or helpful in the long term. Also, the available studies focus on overweight and middle-aged adults. So, it's unclear if other populations would reap the same benefits.

Risks of Intermittent Fasting

So, intermittent fasting may have some health benefits. However, research has failed to show that it's more effective for weight loss and cardiovascular health than overall calorie restriction. Also, the weight loss method may come with some risks.

Disordered Eating

Restricting calories can cause intense hunger. You may become preoccupied with food, leading to overeating and weight gain. 

For example, when you don't eat for a long time, your body releases large amounts of the hormone ghrelin, which influences hunger. High ghrelin levels cause many to overeat during their eating windows.

One study published in 2018 in Nutrition, Metabolism & Cardiovascular Diseases followed 112 people on either a calorie-restricted diet or an intermittent fasting regimen for one year. The group practicing intermittent fasting ate either 400 or 600 calories two days per week. 

The researchers found that the groups' weight loss and cardiovascular benefits were similar. However, the intermittent fasting group was hungrier than the calorie-restricted diet group.

Further, a study published in 2022 in Eating Behaviors of 2,762 Canadian adolescents and young adults found intermittent fasting linked to disordered eating.

Although, research has found intermittent fasting is safe if practiced in moderation. Still, extreme weight loss methods can lead to too much weight loss, intense hunger, and nutrient deficiencies.

Sustainability

Some researchers have questioned whether intermittent fasting is better than calorie restriction. Specifically, researchers have wondered whether the weight loss method is feasible long-term. Further, as of 2023, there's a lack of data about how long intermittent fasting works. 

For example, a review published in 2019 in Nutrients found no trials lasting longer than 26 weeks. Also, the researchers reported that the trials didn't later follow up with people to see if they were still fasting or maintaining their weight loss.

Many health benefits of intermittent fasting, like improved blood sugar and cholesterol, can go away a few weeks after you stop and start eating normally.

Sleep Disruption

Several studies have found intermittent fasting can improve sleep quality if practiced mindfully.

However, fasting in ways that go against your body's natural cycle, also called your circadian rhythm, can make it hard to sleep. Poor sleep increases your risk of weight gain, obesity, diabetes, or cardiovascular disease.

According to a review published in 2021 in Nutrients, avoid skipping breakfast and eating late at night, which can disrupt your body's inner clock, whether you're fasting or not. If you're fasting, the researchers suggest an eating window between 8 a.m. and 4 p.m.

Who Shouldn't Try Intermittent Fasting?

In addition to possible health risks, some people should avoid intermittent fasting, including:

• Pregnant or breastfeeding people 
• Older adults
• People who have or recovered from an eating disorder
• People who have diabetes  
• People taking certain medications  

Also, people who fast longer than 16 or 18 hours are more likely to have gallstones and gallbladder surgery than others.

Intermittent Fasting Safety Tips

If you try intermittent fasting, keep the following tips in mind to mindfully practice the weight loss method:

• Check with a healthcare provider before starting any new eating patterns.
• Ease into fasting in phases.
• Consider working on a plan with a healthcare provider, like a registered dietitian nutritionist.  
• Consider your body's internal clock when deciding your eating window.
• Fasting for 12 hours and eating for 12 hours is safe and might be easier to fit into a routine than other plans.  
• Make sure to eat nutrient-dense foods during your eating window.
  

A Quick Review

As of 2023, research has not shown that intermittent fasting has any more long-term health benefits than calorie restriction. What's more, intermittent fasting may lead to disordered eating, rebound eating that causes weight gain, and sleep disturbances.

So, before you try intermittent fasting, check with a healthcare provider and consider working with them on a plan to ease into it.