Preventive Cardiology

Questioning Intermittent Fasting’s Cardiovascular Impact

A new AHA study shocked the world this week, suggesting that intermittent fasting might significantly increase people’s risk of cardiovascular death, sparking a wave of media coverage, and a frenzy of criticisms from the cardiologist and scientific communities.

  • Time-restricted eating, which is a type of intermittent fasting, involves limiting eating to a specific number of hours per day (e.g. 4 or 8 hours) and fasting for the rest of the day.
  • Intermittent fasting has risen in popularity due to a range of reported benefits to weight, cardiometabolic health, energy, and cognition.

This study set out to evaluate whether these perceived short-term benefits might lead to some serious long-term problems. 

A team of researchers from Wuhan University in China analyzed data from around 20k US adults from the 2003-2018 NHANES database (avg. age 49yrs), who had completed two 24-hour dietary recall questionnaires within the first year of enrollment.  

The poor folks who ate all their meals within shorter time frames on the days before those two particular surveys had far worse outcomes over the 8-year median follow-up period.

  • People who ate within an eight hour window had a 91% higher risk of death due to cardiovascular disease.
  • Participants with CVD who ate all their meals within an 8 to 10 hour window had a 66% higher risk of death from heart disease or stroke.

The media quickly jumped all over this story, with a long list of mainstream news outlets detailing how this “healthy” practice might actually be killing people, and even a few cardiology pubs sharing the same conclusion.

However, it didn’t take long for criticisms to start emerging about the study and its media coverage, noting that…

  • These results conflict with far more reliable RCTs that showed intermittent fasting reduces LDL-C, blood pressure, and weight.
  • The study was observational, relied on dietary responses (often unreliable), and didn’t capture the respondents’ baseline cardiometabolic status.
  • The NHANES survey didn’t ask if these people were following time-restricted diets, they just asked what times they ate during two days. 
  • If you’re not participating in intermittent fasting, not wanting to eat for 16 hours could be a disease symptom or a sign of an unhealthy lifestyle.

The Takeaway

Although we still don’t know whether participating in intermittent fasting diets actually almost doubles cardiovascular mortality risks, a big portion of the population now thinks it does.

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