Can intermittent fasting double your risk of dying from heart problems?

Published 22 March 2024 

Limiting the number of hours a day you eat has become a popular way to try to lose weight in recent years. It's called time-restricted eating or intermittent fasting.  

One of the most popular versions is 16:8 fasting, where you only eat during an eight-hour window and fast for the other 16 hours. 

An analysis of previous research in Endocrine Reviews suggests that in the short-term not eating for a longer period of time overnight can improve blood pressure, blood glucose and cholesterol levels. Keeping these factors under control can reduce your risk of heart and circulatory diseases. 

However, until now the long-term impact of this type of intermittent fasting has not been studied.  

This month researchers from Shanghai Jiao Tong University in China presented early findings from a study looking at this question at an American Heart Association conference. What they reported was widely covered in the UK press, because they suggested there is a link between limiting the time you eat and drink to less than eight hours a day and having double the risk of dying from heart and circulatory diseases. 

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.  

People who already had heart and circulatory diseases at the start of the study were also more likely to die from heart and circulatory diseases when they limited their eating window to eight to 10 hours. This increased their risk by 66 per cent.   

How good was the research?

This research has not yet been 'peer-reviewed', meaning carefully checked by fellow researchers, or published in full.   

Any newspaper articles or TV coverage of this will have likely been based on the presentation summary or its press release. This means it's hard to assess how accurate the research is. 

For a start, different figures are given in the summary and the press release.  

The summary says a window of less than eight hours is linked with a 96 per cent increase in the risk of dying with heart and circulatory diseases, while the press release says 91 per cent.  

The summary says for people who already had heart and circulatory disease, an eating window of eight to 10 hours was linked with a 64 per cent increase in this risk, while the press release says 66 per cent. 

One positive aspect of the research was that it included a large and relatively representative group of people: the researchers followed around 20,000 adults in the United States, with an average age of 49. Half of the people included were women and 27 per cent were not White. 

To arrive at their results, the researchers looked at two surveys the study's participants had previously filled in as part of the US National Health and Nutrition Examination Survey, which detailed what they ate over a 24-hour period.  

They then calculated each person's average eating window and looked at who had died, from what cause, during an average follow-up period of eight years. 

A big limitation of this research is that the participants were only asked about what they ate over two days. We do not know if those who reported restricting their eating to an eight-hour window or less continued this for the study period.  

We also know that self-reported information about diets can be unreliable. 

This study is also observational, meaning it cannot show cause and effect, only a link between two factors.  

We do not know from this study if time-restricted eating causes a change in the body that might increase the risk of dying from heart and circulatory disease. Or if those who are more likely to die from heart and circulatory disease, might also be more likely to be on a time-restricted diet.  

For example, someone may have gone on a 16:8 fasting diet because they've been told by their doctor that they need to lose weight and we know that living with excess weight is a risk factor for heart and circulatory disease.  

Or someone might be reporting time-restricted eating because of their work patterns. Perhaps, they are a night worker or long-distance truck driver. Or maybe some participants were skipping meals because they could not afford them. Such work patterns and poverty have been linked to an increased risk of heart and circulatory disease. 

This study seems to go against what previous studies have suggested about the short-term benefits of intermittent fasting, and so more research is needed in this area. 

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How good was the media coverage? 

This study, despite not being published in full, was covered widely in the UK press, including by the Daily Mail, Sky News, The Times, The Independent and The Sun.  

The Times article was relatively balanced, covering the limitations of the study and other reasons why a smaller eating window might be linked with dying from heart and circulatory disease.  

Its analysis concluded that "there's no solid evidence to say you should ditch intermittent fasting if it's helping you to maintain a healthy weight and you feel good doing it", adding that "more research is needed".  

Some of the other coverage was very inaccurate.  

The Independent's headline "Shocking dangers of intermittent fasting diet revealed" was wrong, as the study does not show that this diet causes death from heart and circulatory disease - just that this research showed a link between eating over a period of less than eight hours a day and dying from heart and circulatory disease.  

It also claimed that the study "was published in the American Heart Association Journal", a peer-reviewed journal, when in fact it's only a press release that has been published on the American Heart Association website.  

The Daily Mail also used statistics from the press release and suggests that intermittent fasting directly caused a raised risk, with its headline "Fasting for 16 or more hours per day RAISES risk of dying from heart problems by almost double, 20-year analysis finds".  

This headline also suggests the study followed participants for 20-years when in fact it followed participants for up to 17 years but for an average of eight years.  

The Sun leads with the headline "Skipping breakfast could DOUBLE your risk of dying from heart disease, scientists warn". Neither the study summary nor the press release mention skipping breakfast.  

The BHF verdict 

Victoria Taylor, Senior Dietitian at British Heart Foundation says: "This is not a full paper so we cannot comment fully on the study. However, we know it's an observational study which means it can only show links. We cannot say that the length of the eating window was the cause of the differences seen in deaths from heart and circulatory diseases.

"Time-restricted eating is an interesting but relatively new area. More research is therefore needed to be able to draw firm conclusions about health driven choices to eat within a time restricted window and long-term cardiovascular health.

"Some people use this way of eating to help them reduce their weight but it's not for everyone. When it comes to reducing weight there is no one-size-fits all approach so it's important to find what works best for you. 

"While 'when to eat' is still being researched, what we do know is that 'what we eat' can make a difference to our risk of heart and circulatory diseases.  

"Eating a well-balanced diet is something we can all do to improve our heart and circulatory health. This means including lots of fruits and vegetables, pulses, nuts and seeds, fish and wholegrains, and making sure our overall diet is low in sugary, salty and fatty foods." 

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