For about a decade now, the practice of intermittent fasting — a type of time-restricted feeding that typically entails fasting for around 16 hours of every 24-hour day — has been a popular method for bodybuilders, strength athletes, or anyone seeking to lose body fat. The allure is simple enough; past science has found that “IF” may have compelling weight management and general health benefits. (1)(2)
But the tide might be turning for intermittent fasting. On Mar. 18, 2024, the American Heart Association (AHA) highlighted an in-review study with a shocking headline: That time-restricted feeding may increase your risk of cardiovascular mortality by as much as 91%. You may have seen this news on outlets like WebMD and USA Today.
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But what exactly did the study say, do its claims hold water, and what are the associated health risks for intermittent fasting, if any? Here’s what you need to know.
Editor’s Note: The content on BarBend is meant to be informative in nature, but it should not be taken as medical advice. When starting a new training regimen and/or diet, it is always a good idea to consult with a trusted medical professional. We are not a medical resource. The opinions and articles on this site are not intended for use as diagnosis, prevention, and/or treatment of health problems. They are not substitutes for consulting a qualified medical professional.
What the Study Says
The research in question was presented at a Mar. 18-21 AHA conference and was helmed by Dr. Victor Wenze Zhong. (3) Here’s a more detailed look at the claims made by Dr. Zhong and colleagues:
Findings
This research report was created based off of longitudinal, observational data of 20,078 adults. Please note that the full research text is not available as of the time of this article’s publication. The authors compared information on dietary patterns from 2003 to 2018 against data on U.S. deaths from 2003 to 2019. Their primary findings include:
- Those who adhered to time-restricted eating, consuming all their calories within an eight-hour window, had a 91% higher risk of death due to cardiovascular disease.
- The authors indicated that a similar increase exists for people living with heart disease or certain cancers.
- For people currently living with cardiovascular disease, a “feeding window” of eight-10 hours per day was associated with a 66% higher risk of death from either heart disease or stroke.
- Time-restricted feeding did not reduce overall risk of death.
- A feeding window at or above 16 hours per day was associated with lower cancer mortality for cancer patients.
Editor’s Note: The two sources of data utilized by Zhong et al. were the National Health and Nutrition Examination Surveys (NHANES) and the CDC’s National Death Index database.
Limitations
Before you go revamping your entire meal prep plan, know that there are plenty of limitations to the arguments presented by Dr. Zhong and the AHA. While scientific data is always valuable to have, there are some limitations to this study that you should be aware of.
First and foremost, per the AHA itself, “…[limitations] included reliance on self-reported dietary information.” This means that the information obtained from this research came from subjects (over the age of 20) responding to surveys and not from participants in controlled settings or from a more stringently selected population. Moreover…
- The full research text has yet to be published or peer-reviewed in an academic journal.
- This is observational, longitudinal (measured over time) data, which doesn’t present an especially strong causative relationship.
- Subjects were “tracked” for a median period of eight years, reporting only on their dietary behaviors.
- Their data displayed a significant risk of cardiovascular mortality, but their data showed no significant negative impact on all-cause mortality from fasting.
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This presentation from the AHA has drawn criticism from a number of different sources. Speaking to WebMD, Dr. Christopher Gardner, a professor of medicine at Stanford University, regarded the conclusions as “premature and misleading.”
Notably, leading author Dr. Zhong also remarked to WebMD about the limitations of his team’s work. “[Multi-year controlled dietary trials are] challenging if not impossible to conduct,” he said, indicating that the absence of evidence on long-term intermittent fasting behaviors means that people should be “extremely cautious.”
What You Should Do
So, what should you do with this information if you’re an IF devotee? Is it time to hang up the lifting belt and get back into breakfast? Not necessarily. While the headline associated with this report is more shocking than most scientific claims, Dr. Zhong’s work has faced some backlash from the scientific community. More importantly, the purported risks have yet to be substantiated by more credible research methods.
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Intermittent fasting is an accessible, often-effective method of weight management, but it’s hardly a one-size-fits-all dietary approach. If you enjoy practicing IF (or any of its cousins), you shouldn’t let this single data set dissuade you. That said, there’s more than one effective type of diet out there.
Other Types of Diets To Try
There’s no magic behind intermittent fasting; setting distinct “start eating” and “stop eating” times can help people control their caloric intake, which is a method for effecting weight change. But if intermittent fasting isn’t your jam, you may consider trying another dietary protocol with methods that better align with your habits and goals:
Note that “specialty” diets, including but not limited to the ones mentioned above, are not necessarily designed to replicate the benefits of intermittent fasting. Not all dietary protocols are suitable for all individuals. The eating behavior that you select should be sustainable, fulfilling, aligned with your health goals, and, most importantly, supported by scientific evidence.
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References
- Halberg, N., Henriksen, M., Söderhamn, N., Stallknecht, B., Ploug, T., Schjerling, P., & Dela, F. (2005). Effect of intermittent fasting and refeeding on insulin action in healthy men. Journal of applied physiology (Bethesda, Md. : 1985), 99(6), 2128–2136.
- Tinsley, G. M., Forsse, J. S., Butler, N. K., Paoli, A., Bane, A. A., La Bounty, P. M., Morgan, G. B., & Grandjean, P. W. (2017). Time-restricted feeding in young men performing resistance training: A randomized controlled trial. European journal of sport science, 17(2), 200–207.
- 8-hour time-restricted eating linked to a 91% higher risk of cardiovascular death. American Heart Association. (n.d.)
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