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Intermittent fasting may not be as effective for some people as previously thought. Valentina Barreto/Stocksy
  • T​here has been extensive research on different weight-loss methods and their effectiveness.
  • Intermittent fasting (IF) is a popular component of weight loss diets, but researchers are still working to understand its benefits and drawbacks.
  • Data from a recent study found that only eating in certain time frames may not significantly contribute to weight loss.
  • Reducing calories and the number of large meals may be more effective than IF for weight loss, the study suggests.

Weight loss is sometimes necessary for people to maintain a healthy weight, and people can use a wide variety of methods to lose weight.

Intermittent fasting, or only eating during specific time intervals, is one of the methods that has increased in popularity in recent years. However, researchers are still working to understand if and how the timing of eating impacts weight loss.

A recent study published in the Journal of the American Heart Association found that the frequency and size of meals had a more significant impact on weight gain than the time window of eating.

The results indicate that restricting eating to certain times of day with intermittent fasting may be ineffective for people to lose weight in the long term.

Help is available

Eating disorders can severely affect the quality of life of people living with these conditions and those close to them. Early intervention and treatment greatly improve the likelihood of recovery.

Anyone who suspects they or a loved one may have an eating disorder can contact the National Alliance for Eating Disorders, which offers a daytime helpline staffed by licensed therapists and an online search tool for treatment options.

For general mental health support at any time, people can call the Substance Abuse and Mental Health Services Administration 24 hours a day at 1-800-662-4357 (or 1-800-487-4889 for TTY).

Many other resources are also available, including:

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Intermittent fasting involves only eating during specific time intervals. There are many ways to do intermittent fasting; it can mean not eating on certain days or only eating food at certain times of the day. Some people seek to use IF to lose weight or maintain a healthy weight.

Some evidence suggests that intermittent fasting can help people lose body fat and may help reduce the risk of type 2 diabetes and cardiovascular disease.

However, researchers are still working to understand the potential dangers of intermittent fasting and how to weigh these risks against the potential benefits. Overall, this is an area where there is a need for more data.

Beata Rydyger, a registered nutritionist based in Los Angeles, CA, and clinical nutritional advisor to Zen Nutrients, who was not involved in the study, pointed out a challenge with studying dietary behaviors to Medical News Today:

“Generally speaking, diets are more difficult to study because dietary changes don’t have an immediate effect on health. Most study participants find it hard to track what they eat, and few can adhere to a diet for long enough for beneficial effects to be measured.”

“Proponents of intermittent fasting highlight a range of potential benefits, some of which are supported by research, including improvements in weight loss, thinking and memory, type 2 diabetes, tissue health, and even physical performance.”
— Beata Rydyger, nutritionist

T​his study included 547 participants recruited from three different health systems.

Researchers collected information on participants through electronic health records and the use of a specialized mobile app called Daily24. Participants could record when they ate, meal size, the times they went to sleep, and when they woke up.

For each meal recorded, participants estimated meal size as less than 500 calories (small), 500-1,000 calories (medium), or greater than 1,000 calories (large).

Study author Dr. Wendy Bennett, elaborated on their research methods to MNT:

“We designed an app to collect ‘timing of eating,’ and when participants input the timing, we also asked them the size of the meal (small, med, or large). Participants from 3 health systems used the app for 6 months. We linked the app data with survey data with electronic health records.”

Dr. Bennett said that they then analyzed the link between eating intervals, including the participants’ total eating window, the time between their wake-up and bedtime, and the time between their last meal and bedtime, with changes in their weight over about six years.

The researchers found that the timing from the first meal of the day to the last meal of the day was not associated with changes in weight. However, they did find that eating more frequent, larger meals were associated with weight gain.

“The main clinical implication is that restricting your window of eating (i.e., eating over less time, having more fasting time) may not reduce weight gain over time. While eating more medium or large meals is associated with weight gain over time. And more smaller meals are associated with weight loss over time.”
— Dr. Wendy Bennett

I​n some of their analysis, the researchers found that eating sooner after waking up and having a longer time between a final meal and going to bed may be associated with less weight gain.

Dr. Katherine Saunders, co-founder of Intellihealth and Obesity Physician who practices at Intellihealth’s telemedicine practice, Flyte Medical, who was also not involved in the study, noted to MNT that the main finding was not surprising.

“The investigators found an association between eating more frequent and larger meals and weight gain, suggesting that total overall caloric intake is the major driver of weight gain. This is not surprising,” she said.

“What is more interesting is that participants with [a] shorter time from wake up to first meal and with longer time from last meal to sleep appeared to experience less weight gain, a trend suggesting that eating earlier in the day might facilitate weight control.”
— Dr. Katherine Saunders

Data on intermittent fasting is still emerging, so no one study offers all the proof that the method is effective or ineffective. This particular study also had several limitations to consider.

First, researchers could only analyze data from study participants who downloaded and used the Daily24 app. This exclusion may have impacted the study population and results.

They only recruited participants from three health systems, meaning the results cannot necessarily be generalized. Almost 78% of participants were women and white, indicating the need for more diverse future studies.

The study also had a relatively short follow-up time, leading to fewer weight measurements and declines in measurement precision. Researchers were also unable to measure participants’ intentions to lose weight before their enrollment in the study.

The way researchers measured eating periods could not evaluate more complex fasting methods. Data also relied on participants’ self-reporting, and food was not standardized or assessed for quality.

“This study did not specifically assess patterns like intermittent fasting. We also did not assess diet quality for the meals reported in the app,” Dr. Bennett noted to MNT.

“Randomized controlled trials that adjust for caloric intake are needed to further test the role of timing of eating in weight gain prevention and also weight loss,” she added.

This study indicates that other methods of losing weight may be more effective than intermittent fasting. Regardless of weight goals, people can use various methods to stay healthy and manage weight.

F​or some, this could mean incorporating intermittent fasting, but others may choose different strategies. Dr. Bennett said that self-monitoring was key to weight loss.

“Other studies do show that people might be able to use time-restricted eating or intermittent fasting to help them reduce their caloric intake and thus lose weight, so it can still be a helpful weight-loss tool for some people who can adhere to it. The cornerstone of weight loss continues to involve self-monitoring,” she said.

Dr. Saunders further noted that people respond differently to different weight loss methods, and it’s not a one-size-fits-all approach.

“There are so many factors affecting weight regulation so successful weight loss needs to address all of these in a personalized way. There is no ‘best diet,’ and different people respond differently to any weight loss approach, whether it’s a diet, an exercise routine, an anti-obesity medication or even bariatric surgery.”
— Dr. Katherine Saunders