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A new study has challenged the alleged health benefits of intermittent fasting, a popular diet often praised by celebrities and health gurus alike.
Intermittent fasting is a well-known practice in which you eat all your food in an eight-hour window and fast for the remaining 16 hours of the day. However, a study from the American Heart Association published on Monday 18 March has found that limiting mealtimes to just eight hours a day was linked to a 91 per cent increase in risk of death from heart disease.
Researchers, led by Dr Victor Zhong of the Shanghai Jiao Tong University School of Medicine,analysed approximately 20,000 adults in the US with an average age of 49 years who had followed intermittent fasting, also known as the 16:8 plan.
According to the study - which was presented at the AHA’s Epidemiology and Prevention conference in Chicago, Illinois - those who limited their eating to eight hours a day were 91 per cent more likely to die from cardiovascular disease than those who ate across 12 or 16 hours. Among participants with existing cardiovascular disease, an eating duration between eight and 10 hours per day was also associated with a 66 per cent higher risk of death from heart disease or stroke.
Meanwhile, people with cancer who ate for more than 16 hours a day were less likely to die from the disease. Researchers also found that time-restricted eating did not reduce the overall risk of death from any cause.
“Restricting daily eating time to a short period, such as eight hours per day, has gained popularity in recent years as a way to lose weight and improve heart health,” said senior study author Dr Zhong. “However, the long-term health effects of time-restricted eating, including risk of death from any cause or cardiovascular disease, are unknown.”
“We were surprised to find that people who followed an eight-hour, time-restricted eating schedule were more likely to die from cardiovascular disease. Even though this type of diet has been popular due to its potential short-term benefits, our research clearly shows that, compared with a typical eating time range of 12-16 hours per day, a shorter eating duration was not associated with living longer,” he said.
The study analysed data from participants in the 2003-2018 National Health and Nutrition Examination Surveys, and compared it to the Centers for Disease Control and Prevention’s National Death Index database on people who died in the US from 2003 through December 2019.
Researchers acknowledged that the study was limited in its findings because it relied on self-reported dietary information, as well as failed to focus on other factors that may play a role in participants’ health.
“Overall, this study suggests that time-restricted eating may have short-term benefits but long-term adverse effects. When the study is presented in its entirety, it will be interesting and helpful to learn more of the details of the analysis,” said Dr Christopher D Gardner, the Rehnborg Farquhar Professor of Medicine at Stanford University.
“One of those details involves the nutrient quality of the diets typical of the different subsets of participants. Without this information, it cannot be determined if nutrient density might be an alternate explanation to the findings that currently focus on the window of time for eating. Second, it needs to be emphasised that categorisation into the different windows of time-restricted eating was determined on the basis of just two days of dietary intake,” he said.
Approximately half of the participants were men and half were women. Around 73 per cent of the participants were non-Hispanic white adults, while 11 per cent were Hispanic. Eight per cent of participants were non-Hispanic Black adults, and nearly seven per cent of adults identified as another race.
“It will also be critical to see a comparison of demographics and baseline characteristics across the groups that were classified into the different time-restricted eating windows,” added Gardner. “For example, was the group with the shortest time-restricted eating window unique compared to people who followed other eating schedules, in terms of weight, stress, traditional cardiometabolic risk factors or other factors associated with adverse cardiovascular outcomes?
“This additional information will help to better understand the potential independent contribution of the short time-restricted eating pattern reported in this interesting and provocative abstract.”
In June 2023, a similar study analysed the weight loss results for adults with obesity who participated in intermittent fasting, compared to traditional calorie counting. The results, which were published in the journal Annals of Internal Medicine, found that those who engaged in eight-hour time restricted eating had improved insulin sensitivity compared to those in the control group who ate their calories any time over 10 or more hours a day.
FAQs
According to the researchers' presentation (PDF, 373KB, 1 page), people who limited their eating window to less than eight hours a day had a 91 per cent (almost double) increased risk of dying from heart and circulatory diseases, compared to those who had a more typical eating window of 12 to 16 hours.
Did the new study find no benefit to intermittent fasting? ›
Research presented this week immediately drew doubt and critiques from experts by suggesting that eating within an eight-hour window or less was significantly associated with a 91% increased risk of dying from cardiovascular disease, when compared with eating over a 12- to 16-hour period.
Are there any dangers to intermittent fasting? ›
Intermittent fasting may offer health benefits for some people. But it can also lead to greater hunger, headaches, fatigue, and mood issues. It could also cause malnutrition if you don't do it correctly.
What is the controversy with intermittent fasting? ›
A new study links intermittent fasting to a higher risk of early death instead of longevity. Some experts are skeptical, citing major limitations with the study like other lifestyle variables. It's too early to say if fasting has long-term risks, so focus on what you eat instead of when.
Why don t doctors recommend intermittent fasting? ›
Intermittent fasting is safe for many people, but it's not for everyone. Skipping meals may not be the best way to manage your weight if you're pregnant or breast-feeding. If you have kidney stones, gastroesophageal reflux, diabetes or other medical problems, talk with your doctor before starting intermittent fasting.
Why are they saying intermittent fasting is bad for your heart? ›
The scientists found that people who followed a 16:8 diet, or ate only within an eight-hour window, had a 91% higher risk of dying from cardiovascular disease compared to people who ate across 12 or 16 hours.
Why I don't recommend intermittent fasting? ›
Risks of Intermittent Fasting
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.
What are 5 cons of intermittent fasting? ›
Other side effects can include insomnia, irritability, headaches, and nausea. For many, IF also may not be sustainable for the long term. Some may find it challenging to fast while keeping up with family and social obligations.
What are the dark side of fasting? ›
A new study finds that intermittent fasting made increase risk of cardiovascular disease when practiced over several years. Restricting eating to eight or fewer hours a day, a type of intermittent fasting, may raise the risk of dying prematurely from heart disease over the long term, a new study suggests.
What is the warning about intermittent fasting? ›
Intermittent fasting — when people only eat at certain times of day — has exploded in popularity in recent years. But now a surprising new study suggests that there might be reason to be cautious: It found that some intermittent fasters were more likely to die of heart disease.
Extreme hunger, excessive weight loss, dehydration, low blood pressure, and weakness can be adverse health effects of fasting. If fasting is impacting your emotions, decreasing your energy levels, or causing extreme hunger, it may be time to stop.
How can intermittent fasting go wrong? ›
Consuming too many calories
Many misunderstand the concept of this diet and end up overeating during the permitted hours, thinking they deserve it or that they can eat whatever they want. Others feel intense hunger after fasting and quickly consume excess calories unknowingly.
Why intermittent fasting is not sustainable? ›
Therefore, when we fast, we reduce the effectiveness of protein synthesis, which negatively affects the amount of muscle mass we can retain during a calorie deficit (eating fewer calories than we are burning off). This, in turn, can reduce our metabolism and make achieving sustainable weight loss more difficult.
Is there anything negative about intermittent fasting? ›
As much as IF is filled with benefits, there are mild side effects that can happen during fasting, which do not generally require medical or surgical treatment. Possible side effects can include dizziness, nausea, insomnia, headache, weakness, etc.
Why is 16 hours the magic number for fasting? ›
While both 12-hour and 16-hour fasting can promote fat burning, it's possible that a 16-hour fast may be more effective. This is because the longer fasting period may lead to a greater depletion of glycogen stores, which can trigger higher levels of fat burning.
Does coffee break a fast? ›
The bottom line. You can drink moderate amounts of black coffee during fasting periods, as it contains very few calories and is unlikely to break your fast. In fact, coffee may enhance the benefits of intermittent fasting, which include reduced inflammation and improved brain function.
Are there any proven benefits of intermittent fasting? ›
Studies discovered that intermittent fasting boosts working memory in animals and verbal memory in adult humans. Heart health. Intermittent fasting improved blood pressure and resting heart rates as well as other heart-related measurements. Physical performance.
What is the research for intermittent fasting 2024? ›
An analysis of over 20,000 U.S. adults found that people who limited their eating across less than 8 hours per day, a time-restricted eating plan, were more likely to die from cardiovascular disease compared to people who ate across 12-16 hours per day, according to preliminary research presented at the American Heart ...
Why intermittent fasting stopped working? ›
If you've tried intermittent fasting but aren't losing weight, possible reasons why include overeating during your eating window and poor food choices. To help, you can try eating fewer calories, work on balancing your meals, or create a smaller or larger eating window.
