New research on intermittent fasting made splashy headlines last week. The abstract, presented at an American Heart Association conference, found that intermittent fasting—specifically, the restriction of food consumption to an 8-hour period each day—was associated with a 91% increase in risk of cardiovascular death. (Insert needle-scratch.)
This is shocking intel, not just because the statistic is so staggering, but because it flies in the face of what we’ve previously known to be true about the benefits of intermittent fasting, which would suggest it has the opposite impact on heart health. The practice, in fact, is supposed to be good for your heart.
However, experts say that prior research shouldn’t necessarily be discarded in favor of these new findings and that you don’t need to panic if you get your calories within a restricted window of time each day. Here, they unpack everything we know to date on intermittent fasting’s impact on heart health.
What is intermittent fasting?
Generally speaking, intermittent fasting is a dietary approach where you are in a fasted state for some period of time, says Julia Zumpano, RD, a preventive cardiology nutritionist at Cleveland Clinic. The precise period of time depends on the type of intermittent fasting you’re doing—there are several different types—but one popular approach involves restricting calories to an eight-hour window each day. For example, 12 p.m. to 8 p.m. It doesn’t involve any dietary restrictions beyond eating within a specific time window, and some people find this easier to adhere to than trying to cut out specific foods or counting calories. However, it can result in an overall reduction in caloric intake—some research indicates that people end up cutting out about 300 to 500 calories by intermittent fasting.
What has prior research said about intermittent fasting’s impact on heart health?
Prior, well-controlled, short-term studies have shown that intermittent fasting can result in improvements in body weight, insulin resistance, blood pressure, and some markers of inflammation, a.k.a. “a number of surrogates for heart health that tend to be associated with improved cardiovascular outcomes in the long term,” says Sean Heffron, MD, preventive cardiologist and director of fitness-focused cardiology at the Center for the Prevention of Cardiovascular Disease at NYU Langone Heart.
Longer-term data is scarce in humans due to the general limitations of diet and nutrition studies (more on that to follow), but we do have longer-term data based on animal studies. “Lots of these studies show that life-long adherence to limited energy intake is associated with greater lifespan,” Dr. Heffron says.
What did this new research find?
This new study aimed to look at long-term data in humans to fill the gaps in our understanding of intermittent fasting’s impact on health. It included data collected as part of the National Health And Nutrition Examination Survey, which asked 20,000 adults of varying ages, sexes, and ethnicities what they ate during an average period of eight years.
During that time period, participants reported what they had eaten in two separate interviews less than two weeks apart. If they reported having eaten within a restricted eight-hour window, researchers generalized that eating pattern to their lives overall, essentially labeling them as intermittent fasts.
Researchers then looked at who had died subsequent to filling out the surveys to see whether or not their engagement in this form of intermittent fasting was associated with overall death, cardiovascular death, and death from cancer, says Dr. Heffron. “They found that there were associations, meaning that restricting food consumption over a very short period was associated with worse outcomes,” he says.
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