Intermittent fasting is a popular diet that's simple in theory and execution: you consume calories during a limited time window of the day, and outside of that you don't eat at all.
This regimented approach to dieting has helped many people achieve the discipline they need to lose weight, and some research has shown that it can provide a myriad of health benefits, including improved blood pressure.
But a new yet-to-be-published study, presented this week at a meeting of the American Heart Association, suggests that intermittent fasting could have serious consequences for your cardiovascular health.
In an analysis of over 20,000 US adults, the study found that those who eat in just an eight hour window or less per day — thereby fasting for at least 16 hours — had a 91 percent higher chance of dying from heart disease.
This also appeared to increase the risk of dying from heart disease or stroke for patients who already had heart disease by 66 percent. Cancer patients who intermittently fasted this way also had a higher risk of cancer mortality.
"We were surprised to find that people who followed an 8-hour, time-restricted eating schedule were more likely to die from cardiovascular disease," study lead author Victor Wenze Zhong, chair of the Department of Epidemiology and Biostatistics at the Shanghai Jiao Tong University School of Medicine in China, said in a statement about the work.
"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."
On its face, those findings are startling, especially given the diet's rising popularity. But as Zhong cautions, the findings aren't conclusive.
"Although the study identified an association between an 8-hour eating window and cardiovascular death, this does not mean that time-restricted eating caused cardiovascular death," he said in the statement.
Some of his colleagues in the field are more skeptical. As noted by Christopher Gardner, the director of nutrition studies at the Stanford Prevention Research Center, because the study has not been released yet, it's unclear how the researchers could have controlled for demographic and lifestyle differences that could explain the rise in mortality.
"Did they all have the same level of disposable income and the same level of stress," Gardner told The Washington Post. "Or is it that the people who ate less than eight hours a day worked three jobs, had very high stress, and didn't have time to eat?"
Elsewhere in science journalism, Matthew Herper at Stat bluntly wrote of the study: "you shouldn't be wasting brain glucose thinking about it."
Herper notes that the study relied on self-reported diet data from respondents — and let's be real, most of us aren't honest, intentionally or not, about our eating habits. Sometimes we forget, and sometimes we lie to ourselves.
According to Herper, who received an abstract of the study from the AHA, it also appears the researchers didn't specifically ask if the respondents were intermittently fasting, but instead looked for people who ate only during a short window of the day. That means that people who skipped meals for other reasons — poverty, eating disorders, et cetera — could have slipped through the cracks. And let's not forget that some people who realize they're suffering from poor cardiac health might turn to fad diets, meaning the apparent causality could be reversed if they later die from a heart attack or stroke.
"This was a neat finding that should tell people working in nutrition to look harder at this topic," Herper concluded. "For everyone else, it doesn't really say anything at all."
All told, the still results may not yet be actual cause for alarm — but they do highlight the difficulties of nutrition science, and the need to research intermittent fasting further.
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