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- Researchers report that intermittent fasting is no more effective for weight loss than other dietary routines.
- Experts say intermittent fasting can help people lose weight, but the effects are usually short-lived.
- They add that a healthy diet is essential, regardless of the dietary plan a person has adopted.
Intermittent fasting is widely touted as an effective weight loss strategy, but new research suggests these benefits may be exaggerated.
A new review of evidence found that intermittent fasting is not superior to other dietary patterns for weight loss.
The researchers said that intermittent fasting is unlikely to lead to greater weight loss in people who are diagnosed with overweight or obesity when compared to traditional dietary advice or not adopting any dietary plan at all.
The findings were published on February 15 in the Cochrane Database of Systematic Reviews.
“Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight,” said lead author Luis Garegnani, PhD, director of the Universidad Hospital Italiano de Buenos Aires Cochrane Associate Centre in Argentina, in a news release.
Experts not involved in the study agreed with the researchers’ conclusions.
“The rules [for intermittent fasting] are easy, and if it works for patients, I encourage them to try it. However, intermittent fasting is usually not the ‘game-changer’ people are looking for,” Sun Kim, MD, an associate professor of medicine at Stanford University, told Healthline.
Mir Ali, MD, a bariatric surgeon and the medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, CA, said he was surprised by the study findings, but noted that intermittent fasting only works when a person adheres to a healthy lifestyle.
“In my experience, time-restricted eating can be beneficial, particularly when combined with a healthy diet,” Ali told Healthline. “The quantity and quality of calories consumed are critical. If a person continues to consume the wrong foods, they will likely see limited results.”
Intermittent fasting benefits often short-lived
To reach their conclusions, the researchers analyzed data from 22 randomized clinical trials involving nearly 2,000 adults from North America, Europe, China, Australia, and South America.
Their review compared intermittent fasting with traditional dietary advice as well as no intervention.
The data involved various forms of intermittent fasting, including alternate-day fasting, periodic fasting, and time-restricted feeding.
Most of the studies followed participants for up to 12 months.
The researchers reported that intermittent fasting resulted in “little to no difference” in baseline weight loss when compared to regular dietary advice. They added that there was also “little to no difference” in comparable quality of life.
They reported similar results when intermittent fasting was compared to people who weren’t following any official dietary advice.
The researchers cautioned against what they described as the online hype surrounding intermittent fasting.
“Intermittent fasting may be a reasonable option for some people, but the current evidence doesn’t justify the enthusiasm we see on social media,” Garegnani said in a statement.
Experts said that intermittent fasting can produce weight loss results over a short term, but maintaining that success long term can be difficult.
“Losing weight is hard, and there is no shortcut,” said Kim. “There have been studies showing that intermittent fasting is associated with weight loss (usually not more weight loss than other strategies) in the short term.”
However, Kim added, “In most weight loss interventions (without medications), there is some weight regain between 6 to 12 months.”
“While the rules of intermittent fasting are easy to follow, it’s difficult to maintain long-term,” she said.
Kristin Kirkpatrick, president of KAK Consulting and a registered dietitian at the Cleveland Clinic Department of Wellness & Preventive Medicine, agreed that there are limitations to intermittent fasting.
“Intermittent fasting alone, without dietary intervention suggestions, adequate sleep, and regular forms of exercise may not be as reliable,” she told Healthline. “The point is — it’s a variety of factors that may lead to weight loss, often not just one component.”
David Cutler, MD, a family medicine physician at Providence Saint John’s Health Center in Santa Monica, CA, said the most important factor is how much you eat, not when you eat.
“The key point here is that weight loss occurs because people eat fewer calories overall, not because fasting itself has a unique fat-burning effect,” he told Healthline.
“For some people, intermittent fasting makes adherence to a diet easier. This may be because there are fewer meals, or perhaps their appetite may adapt over time, or simply less late-night eating. If it helps someone maintain a calorie deficit long-term, it can be effective.”
What to know about intermittent fasting
Intermittent fasting (IF) is a plan where a person eats only during a certain time frame and fasts the rest of the day, only consuming water or other calorie-free liquids such as herbal tea or black coffee.
The routine generally doesn’t focus on what foods a person eats. It centers on when a person eats.
There is a wide variety of fasting plans. Some of the most common forms include:
16/8 method
The 16/8 intermittent fasting plan involves an 8-hour eating period and a 16-hour fasting period.
Some people do this by skipping breakfast, but you can also do the reverse and skip dinner or eating your day’s final meal in the late afternoon.
5:2 diet
With the 5:2 method, you consume only 500 to 600 calories on two nonconsecutive days of the week but eat as usual the other 5 days.
Eat-stop-eat
This protocol involves fasting for 24 hours once or twice per week. Because this is a slightly more advanced version of fasting, you should only try this if you’re comfortable with the practice.
Physiological changes
When a person fasts, a number of changes happen in the body. These include:
- increased human growth hormone (HGH) levels
- decreased insulin sensitivity and improved insulin levels
- initiated cellular repair processes
- changes in the function of genes pertaining to longevity and disease prevention
Benefits
Intermittent fasting can help a person lose weight, at least in the short term. The weight loss usually occurs when people eat fewer calories overall.
Some research indicates that intermittent fasting can help boost brain health and heart health.
A recent study found that intermittent fasting can help reduce symptoms and inflammation in people with Crohn’s disease.
Kim said that intermittent fasting can also help lower blood sugar and improve sleep quality.
“Most of us ‘graze eat’ all day and only stop during sleep. The internal clocks in our organs prefer times of eating and times of fasting,” she said.
Kirkpatrick said intermittent fasting can be beneficial in helping people regulate their eating habits.
“I’ve seen a lot of success especially in my patients that come to me struggling with late-night eating,” she said. “Because intermittent fasting often means ending your eating at an earlier time, the late-night eating pattern is often eliminated.”
Expert tips for weight loss
If you’re interested in trying intermittent fasting for weight loss, experts recommend starting slowly and consulting with your doctor first.
“I advise patients interested in time-restricted eating to start with a shorter fasting window, such as 8 hours, and gradually expand toward a goal of 12 to 16 hours,” said Ali.
“Most people suggest eating in an 8-hour window of time,” added Kim. “This is difficult to adhere to at first, so start eating within a 12-hour window and decrease that window gradually. It’s best to eat breakfast, but most people prefer an eating window between noon and 8 p.m. because dinner tends to be more social.”
Experts agreed that eating healthy foods is key to any fasting or dietary plan.
“Look at added sugar intake and see where you can cut, decrease processed food intake, try to make/prepare your own food, eat two fruits and three different vegetables daily,” said Kim.
“Maintaining proper nutrition is essential, with an emphasis on protein and vegetables while minimizing carbohydrates and sugars,” added Ali.
The advice is similar for people who can’t or don’t want to embark on an intermittent fasting plan.
“If intermittent fasting is not feasible, I recommend limiting food intake late at night,” said Ali. “Regardless of the timing, eating the right foods remains necessary to achieve meaningful weight loss.”
“There are many options for weight loss, but I always start by advising on what life change strategy do you think you can maintain long term,” said Kim. “Gimmicks will last short term.”
Kim added that weight loss drugs can be helpful, but a healthy lifestyle is still the most important factor.
“In an era of GLP-1 medications, I think it’s hard to ignore that these medications will be more effective to aid weight loss than other strategies without medications,” she said. “However, medications should be taken on a foundation of healthy eating and exercise.”
Kirkpatrick said the best plan is the one that people believe in and will follow.
“There is no one-size-fits-all approach, and different variations of lifestyle change work with different people,” she said. “The key is to determine if intermittent fasting and other lifestyle factors may work. I think working alongside someone you trust, who uses evidence-based approaches, is a good first step.”
Cutler echoed these remarks. “The best diet is the one someone can sustain, while preserving lean mass and nutritional adequacy,” he said.
