The Intermittent Fasting Diet: Is It All It’s Cracked Up to Be?

Along with weight loss trends like GLP-1 drugs or the keto diet, one fad that has recently gained notoriety is intermittent fasting (also known as IF). Unlike a traditional diet, intermittent fasting ("IF," also known as Time Restricted Eating, or TRE) doesn't necessarily focus on what people eat, but when. It's effectively an eating schedule, requiring people to only eat during certain times, and enforcing fasting stints during certain time frames.

Dr. Amy Lee, Chief Medical Advisor at Lindora, attributes the rise in popularity of intermittent fasting to new findings and positive testimonies from athletes who adhere to the diet: "Intermittent fasting is growing in popularity because it works and data has shown benefits in both weight management and mental clarity and longevity," she tells Woman's World. "Recently, athletes have joined the movement and their testimonials have fueled the recent buzz."

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Since the intermittent fasting diet doesn't tell you what foods are allowed, it can be easy to think you don't need to watch what you eat. But with all your eating condensed into a short period of time every day, it's even more important to make sure you're consuming wholesome, nutrient-dense foods, like the Mediterranean diet.

Intermittent Fasting Is More of a Lifestyle, Than a Diet

Intermittent fasting has dieters fast during certain time frames, with scheduled meal times throughout the day or week. According to a blog post from Johns Hopkins Medicine, some might even choose to eat just one meal per day, a few times per week.

In theory, the lifestyle is based on the idea that the human body is able to go for long periods of time without eating. And due to many people becoming increasingly sedentary with more snacks and processed foods, it could help with weight loss, and maintaining goal weights.

"There is definitely a population that would benefit from this regimen and for those who love it, it is convenient and easy," Dr. Lee says. "Also, when you do it long enough, the restricted eating times actually can help with suppressing one’s appetite, so you don’t feel the need to eat during the hours of fasting. Make sure you are well hydrated throughout the day as the body does lose water from normal activities. "

Intermittent Fasting Seems To Be Safe

Unlike most diets, time restricted eating is a tried and true approach. Though it has recently gained popularity, it's been around for hundreds of years. "Intermittent fasting has been practiced in various forms for centuries, and daily fasting for 16 to 18 hours is generally considered safe for most healthy adults," Kelsey Costa, MS, RDN, a registered dietitian nutritionist and founder of Dietitian Insights explains via Woman's World.

"Current research suggests that confining daily food consumption to a six-to-eight-hour window might offer health benefits such as reducing the risk of certain cancers, heart disease, obesity, and hypertension."

There Are a Few Different Intermittent Fasting Plans

There isn't just one way to approach intermittent fasting. One common strategy, for example, is the "daily approach," when people eat only during a six- to eight-hour window, per Johns Hopkins Medicine. 16/8 fasting, for example, involves eating for eight hours of the day, and fasting for 16. There's also the 5:2 approach, which has dieters eat regularly for five days a week, and only eating a small 500 to 600 calorie meal the other two days. Then, there are the 24-, 36-, 48-, and 72-hour fasting periods, though those generally are not recommended. Each approach should also only be tried with medical permission.

"There are several ways to implement intermittent fasting, but all involve choosing regular time periods to eat and fast either during a day or during a week," Dr. Romilly Hodges of Sonoran University tells Woman's World.

Eating Earlier May Be Better

However, most dieters focus on eating earlier in the day for an intermittent fast. "Many also skip breakfast and choose to start their fast in the early afternoon," Dr. Jessica Kovalchik, also of Sonoran University, adds. "Recently, research has shown that it is better to break your fast earlier in the day (by eating breakfast) and instead fasting later (so foregoing a late dinner)."

For Many, Intermittent Fasting Is the Key to Weight Loss

Science shows that time restricted eating is proven to be a safe way to lose weight. A blog post from the University of Illinois explains that it's as effective as counting calories, helping some lose up to eight percent of their body weight, while also lowering blood pressure and blood sugar.

"Around 12 hours after eating, the body experiences a metabolic shift and starts to burn fats," Dr. Hodges says. "Prolonging the time that your body is in a fat-burning state can aid with weight loss."

Intermittent Fasting May Be Effective Long-Term, But It Depends On How and What you Eat

But does an intermittent fasting diet work for weight loss long-term? Dr. Kovalchik says it depends: "It being sustainable is up to the person who is doing it. Some studies have shown that individuals who do shift work have a harder time maintaining a 16:8 eating pattern daily but can do it for 3-5 days per week," she explains.

Research Has Shown Time Restricted Eating Has Other Physical and Mental Benefits

Weight loss isn't the only positive outcome of intermittent fasting. A study published in the Journal of Yeungnam Medical Science also shows it lowers blood sugar levels, inflammation and other chronic issues.

"Short term, it seems to have positive effects on everything from weight management to chronic disease; we just don’t know how that translates long term yet," Dr. Kovalchik says.

"It is exciting to see additional scientific investigations that are exploring other possible benefits," Dr. Hodges adds.

Intermittent Fasting Comes With Possible Side Effects

Intermittent fasting isn't for everyone, and short-term side effects should be monitored. According to a blog post from Harvard University, IF often makes people feel sick in the beginning — it can lead to headaches, fatigue, moodiness, and constipation. It can also trigger overeating, cause older adults to lose too much weight, and it can mess with medications. Therefore, an expert's guidance is absolutely necessary.

"It's generally recommended that you check with a medical professional if you're thinking about fasting for more than 36 hours," Dr. Costa adds. "Fasting for longer periods of time may lead to nutrient deficiencies and other negative health effects if not carefully managed."

Intermittent Fasting May Not Be Safe For People With Some Medical Conditions

For some, IF may not be the move. Dr. Costa explains that not eating for long periods of time can negatively impact those with certain medical conditions.

Long-Term, IF May Pose Cardiac Risks

There are long-term side effects that can occur from time restricted eating. According to the American Heart Association, a study from China's Shanghai Jiao Tong University School of Medicine showed those who restricted eating hours to less than eight hours daily had a 91 percent greater chance of developing fatal heart disease. This is compared to those who didn't partake in intermittent fasting.

It's important to note this was preliminary data that dieters self reported: "When the study is presented in its entirety, it will be interesting and helpful to learn more of the details of the analysis,” Christopher D. Gardner, Ph.D., FAHA, the Rehnborg Farquhar Professor of Medicine at Stanford University in Stanford, told the Heart Association.

“In the long term, what it does is reduces those risk factors for heart disease and reduces the risk factors for diabetes and so forth — but in the short term, while you’re actually doing it, your body is in a state where it’s at a higher risk of having problems,” Dr. Benjamin Horne, a research professor at Intermountain Health in Salt Lake City, told NBC News. "[This finding] doesn’t change my perspective that there are definite benefits from fasting, but it’s a cautionary tale that we need to be aware that there are definite, potentially major, adverse effects.”

As With Most Diets, People With Eating Disorders Are Advised Against Trying It

Even though many weight loss diets tend to come with the risk of developing disordered eating habits, intermittent fasting has a notable correlation. A study posted to the National Library of Medicine looked at the correlation between time restricted eating and eating disorders. And many of the adolescents studied — particularly women — appeared to exhibit disordered eating habits.

"There are some instances where intermittent fasting would not be appropriate, such as those with a current or history of eating disorders as well as in adolescents as they are more prone to disordered eating behavior," Dr. Kovalchik tells Woman's World. "I always recommend working with a Certified Nutrition Specialist? or Dietician who is familiar with IF and can monitor progress."

Intermittent Fasting Can Be a Major Lifestyle Change

Even though TRE doesn't change what you eat, only being able to eat at specific times may result in a huge lifestyle change. According to Drexel University's Nylee Dardarian, it's very hard to stick to for a long period of time. It may change one's social life, and doesn't teach lifelong healthy habits. It also results in low energy levels, making it hard to keep up with daily life activities. "As with any dietary plan, you have to be mindful about putting in nutrients that the body needs," Dr. Lee says.

Time Restricted Eating and Weight Loss Drugs

Those taking weight loss drugs may want to consider intermittent fasting. Weight loss drugs like Ozempic mimic GLP-1 production, which makes people fuller longer, while delaying gastric emptying. And because IF further increases GLP-1 production, this could amplify weight loss results, as shown in a study published to the National Library of Medicine.

Unlike Many Diets, IF Might Help Your Grocery Bill

While many diets involve buying more expensive, healthier foods, intermittent fasting doesn't change what people are eating. Therefore, it's one of few diets that won't raise grocery expenses.

Intermittent Fasting Looks Like a Good Option For Some

Intermittent fasting seems to be safe and effective. However, short-term side effects and long-term mental health should be monitored. And as usual, it should only be done with a doctor's guidance. "Periods of fasting have been part of the human experience since the earliest times. In fact, it is only in more recent decades that food abundance and access have largely eliminated fasting from many people’s lives," Dr. Hodges says.

"I have used intermittent fasting with success in many different individuals," Dr. Kovalchik adds. "However, I don’t tend to prescribe it long term and I also like to cycle it (4 days following IF and 3 days of regular eating window)."

Intermittent Fasting FAQs

Is intermittent fasting safe?

Time restricted eating can be safe, depending on health history and possible eating disorder history. Speak with a doctor before trying the diet, to ensure it's right for you.

What are the caloric restrictions for intermittent fasting?

There are no calorie or food restrictions for intermittent fasting. During a fasting window, however, food is off limits.

How long does it take for intermittent fasting to work?

Results of intermittent fasting vary from person to person. Improved symptoms may take a few days, while weight loss may take up to a month.

What are common mistakes with intermittent fasting?

-Eating unhealthily all the time
-Being unprepared with meal prep
-Eating too few calories
-Restricting and binging
-Making exceptions for eating outside your "food window"

Can I eat whatever I want when intermittent fasting?

There aren't restricted foods for time restricted eating. However, you shouldn't skimp on protein or fiber; or overdo carbohydrates, processed foods and refined sugars.

Related:
“I’m a Dietitian and These Are the 5 Biggest Weight Loss Mistakes People Make”
Paleo and Anti-Inflammatory Diets: What They Do and Don’t Have in Common

This content is not a substitute for professional medical advice or diagnosis. Always consult your physician before pursuing any treatment plan.