Intermittent fasting: Miracle diet or bad for the heart?

Intermittent fasting has been trendy for a while now. These diets limit the hours you can eat in a day and are viewed positively by healthy-aging researchers. They have also been endorsed by all sorts of famous people. A review of studies on intermittent fasting found that it aids weight loss, improves glucose levels and has benefits for people with hypertension. But like many nutrition studies, the precise causes for the changes identified in this research remain elusive, and there’s a scarcity of long-term studies in this area.

At a recent American Heart Association conference, findings from a study on over 20,000 U.S. adults across eight years were shared. People who limited eating to eight hours daily had a 91% higher risk of cardiovascular death. For those with an eating window of over eight but less than 10 hours, the risk rose by 66% compared to those without time restrictions. If confirmed by other studies, intermittent fasting could pose health risks. But this study has yet to be published in a scientific journal or even peer-reviewed by other experts. Limited details about the study are available, which appears to have significant limitations.

To track the diets of study participants, researchers from Wuhan University, Shanghai Jiao Tong University, Northwestern University, Harvard University, and the University of Massachusetts Lowell, analyzed responses from the National Health and Nutrition Examination Surveys (NHANES) between 2003 and 2018. NHANES participants reported their daily eating times in two interviews, and the survey assumes these habits remained constant over the following years. The researchers then compared this data with the Centers for Disease Control and Prevention (CDC) database of deaths in the United States from 2003 to 2019.

Observational studies can identify a connection between two phenomena, yet understanding causality is much more complicated. “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,” said a recent article in Heart Matters, published by the British Heart Foundation. But some people eat this way because they work night shifts or have stressful jobs that limit meal breaks. In such cases, their work conditions can pose a cardiovascular risk, regardless of their diet.

There’s a historical paradox in observational studies, highlighting the need for caution when interpreting recent research on fasting. Studies on alcohol’s health effects have long shown that non-drinkers have higher mortality rates than occasional or light drinkers. However, researchers question this finding due to challenges in identifying non-drinking groups that don’t abstain due to past alcoholism or illness.

Insufficient research on fasting

While animal studies show promising outcomes and human molecular analyzes indicate that fasting triggers the production of protective proteins against certain metabolic and brain diseases, diet research, particularly long-term research, is complex. Senior study author Victor Wenze Zhong, a professor at Shanghai Jiao Tong University School of Medicine, emphasizes the need for long-term studies to fully understand the health effects of fasting and believes that their findings “encourage a more cautious, personalized approach to dietary recommendations, ensuring that they are aligned with an individual’s health status and the latest scientific evidence.” Zhong notes that while the study found a link between certain fasting methods and higher cardiovascular mortality risk, “the long-term health effects of time-restricted eating, including risk of death from any cause or cardiovascular disease, are unknown.”

Other research indicates that intermittent fasting for weight loss may result in more muscle loss compared to longer eating periods. Since muscle health is tied to metabolism, this association might explain the potential connection between fasting and heart issues, though it’s not yet confirmed. Experts generally advise caution when considering fad diets. It’s best to consult a doctor, especially if you have health concerns, before trying a new eating pattern that’s still in early research stages.

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