The American Heart Association now says that people who do intermittent fasting are more likely to die from cardiovascular disease. Is this true?
Anonymous
No! This new information comes from a press release and abstract, not from a full paper. This distinction is important for a few reasons. First, the abstract isn’t peer-reviewed, which means it hasn’t had the critical look a published paper would. Second, perhaps more importantly, an abstract lacks a lot of the details that you would get in a full paper. This means we don’t have all the information we might like in order to evaluate the validity of the study.
Fortunately, there is enough information to know it’s not compelling.
This study uses data from the National Health and Nutrition Examination Survey (NHANES), a nationally representative survey in the U.S. that, among other things, asks about diet. Participants in the survey report their eating patterns in a two-day dietary recall — basically, at the time of the survey, they are asked about what they ate over a prior two-day period, and when. The study uses data from 20,000 participants, and researchers are able to link these people to later mortality data.
The basic finding of the study: the researchers classify people into groups based on how many hours of the day they eat. Are you eating all your calories within eight hours? Eight to 10 hours? And so on. They then compare long-term mortality for individuals who eat in shorter versus longer windows. They find an elevated cardiovascular death risk for those who eat in a very short window (less than eight hours of the day) relative to others. They conclude that time restricted eating, or intermittent fasting, may cause elevated heart disease risk.
This finding has two very basic problems.
First, like virtually all research on nutrition, there is a deep struggle to separate correlation and causality. The group that eats for shorter periods of time is different in many ways — observable and very likely not observable — relative to those that eat for longer periods during the day. It is a reliable fact that we cannot learn anything causal from observational data on nutrition. Period.
But second, and more basic, this is not a study of intermittent fasting. No one is asked if they are intermittent fasting. There is no sense in which we know if people are eating in a limited way on purpose, or if it is just something that happened those two days you interviewed them at random. To draw conclusions from this about ongoing intermittent fasting patterns is just kind of bizarre.
Should you intermittent fast? Up to you! The data doesn’t show evidence that it helps with weight loss, but some people like it. So go ahead if you want to. Don’t worry about dropping dead.
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