You may have seen headlines and social media posts claiming that a scientific study has linked ... [+]
Not so fast. You may have seen headlines and social media posts claiming that a scientific study has linked intermittent fasting to a 91% higher risk of death from cardiovascular disease. But a closer look at this study that was presented at the American Heart Association’s (AHA’s) Epidemiology and Prevention│Lifestyle and Cardiometabolic Scientific Sessions 2024 on March 18 in Chicago, Illinois, reveals a buffet of limitations that make such claims premature.
Intermittent fasting is when you limit your eating to only a certain time period—such as an eight-hour window—each day. The thought is that fasting—meaning not consuming anything with calories—during the rest of the day will give your body more time to burn fat. Those who advocate for such intermittent fasting argue that following such time-restricted eating patterns is more natural. After all, back when humans were cave people, they weren’t able to simply reach over while watching Sexy Beasts on Netflix and shove food into their mouths at any time. Whenever they wanted to eat, they had to actually had get out of their chairs and spend time to hunt and gather things while burning calories in the process.
Scientific studies have indeed suggested that intermittent fasting may have health benefits such as better weight control and reducing the risk of obesity, type 2 diabetes, heart disease and other illnesses with an emphasis on the word “suggested.” These are certainly not foregone conclusions. Plus, a given diet may not work the same for all people. As Buffy Sainte Marie once sang to Big Bird on the TV show Sesame Street, different people, different ways. More studies are needed to better determine the benefits and risks of intermittent fasting and who might benefit from such a diet.
This study recently presented at the AHA meeting in Chicago did raise the possibility that intermittent fasting may have some negative cardiovascular effects. But—and it is a big but one cannot lie—this study has at present some major limitations.
First of all, the study has not yet been published in a scientific journal and thus has not undergone rigorous scientific peer-review. A press release from the AHA described the study as “preliminary research.” The bar for presenting a study at a scientific conference—even a reputable one like an AHA meeting—is a lot lower than that for publishing a study in a reputable scientific journal. It’s sort of like the difference between participating in a pre-season scrimmage and regular season football game. Getting on to the field during a pre-season scrimmage doesn’t mean that you will eventually make the roster for the regular season.
That’s because one cannot yet tell how well done this study was. A presentation at a scientific meeting typically cannot offer enough concrete verifiable details to evaluate the quality of the study and it’s strengths and limitations. So, take anything you hear from a scientific meeting with a grain of salt—that’s figuratively speaking, because too much salt is not good for your cardiovascular system.
Secondly, the study was an observational study, one that can at most show “hmm, that may be interesting” associations but cannot demonstrate cause-and-effect relationships. For the study, a team from Shanghai Jiao Tong University, Northwestern University, Harvard University, the University of Massachusetts Lowell and Wuhan University analyzed responses to the annual National Health and Nutrition Examination Surveys (NHANES) that spanned the years 2003 through 2018 and triangulated it with data from the Centers for Disease Control and Prevention’s National Death Index database on deaths that occurred during the 2003 through December 2019 time period. Their analysis found that people who had reported consuming all of their food within an eight hour time window each day had 91% higher rates of death due to cardiovascular disease compared to those who did not restrict their eating to such a time window. And those who reported eating everything within a more than eight but less than 10-hour time window had died from heart disease or stroke at a 66% higher rate than those who did not enforce such restrictions.
The trouble is one can not tell whether the higher cardiovascular death rates were actually due to the intermittent fasting or something else was going on with the 20,078 people who comprised the sample. This could have been a chicken or egg phenomenon—meaning that it’s not clear which might have come first rather than everyone was eating chicken or eggs. What if, for example, people were doing intermittent fasting because they were already at greater risk for cardiovascular death? Data from NHANES could only provide limited information about the respondents lives. For example, it didn’t go into
Thirdly, the dietary data from NHANES is limited. Unless you were to disguise yourself as a bush and follow each person each and every day, you wouldn’t know how well they were adhering to intermittent fasting, what specifically they were eating each day and how they were eating. People can be notoriously inaccurate about reporting what they are doing each day. There’s a big difference between something like intermittent fasting along with a relatively healthful diet versus intermittent fasting along with an all-doughnut diet.
Finally, a single study is not enough to prove anything. Relying on a single study to draw a strong conclusion would be like declaring that one-hit wonder Chumbawamba would be the next Beatles after hearing the song “Tubthumping.” Instead, you really need to see a phenomenon hold across multiple studies before making a bigger deal about it.
This is yet another example of how the findings from an observational study were blown out of proportion. Sure, there is reason to look closer at whether intermittent fasting may have negative effects. Sure, just because some celebrities and social media influencers have been pushing intermittent fasting doesn’t mean that you should do it automatically too. Sure, one-size-fits-all doesn’t work when it comes to diets. Sure, the science behind intermittent fasting is not definitive yet. Sure, more scientific studies are needed. But the additional studies shouldn’t just be more observational studies. Again such studies are limited in what they can provide. There’s a need for a broader range of studies such as more studies that use laboratory, clinical trial, computer modeling and other artificial intelligence (AI) approaches to provide evidence about intermittent fasting before being too fast and furious about intermittent fasting.
