My wife doesn't follow nutrition research and writing the way I do. She doesn't, for example, have email alerts set up to tell her about new studies and publications. So when she becomes aware of a new study or article, I can usually be pretty sure the item in question is filtering out in to the mainstream consciousness.
Today the item in question is a report from the American Heart Association that engaging in intermittent fasting, the practice of limiting your food consumption to a certain time period, is associated with a significant increase in heart disease. This shocking headline is being reported by the Washington Post, and CNN, and NBC News, and so on and so on. Mainstream consciousness, indeed. These articles suggest that the researches found “that people who adhered to the eight-hour eating plan had a 91 percent higher risk of dying from heart disease compared to people who followed a more traditional dietary pattern of eating their food across 12 to 16 hours each day” and includes quotes from the researches advising those who practice intermittent fasting to be “extremely cautious.” 1
The major problem with these results
though, is that the researchers did not in any way study people who engaged in
intermittent fasting. Nor did they make any attempt to
Intermittent Fasting
Research
Let’s take a moment here to pause
and consider what you as a researcher might do if you wanted to assess the
effects of intermittent fasting.
The best strategy would probably
be to take a bunch of people, record a lot of health data, have them engage in
intermittent fasting for some period of time, and measure those same markers again.
Bonus points if you have a second comparison group alongside them to eat the
same amount of food spread throughout the day. Then you could see if intermittent
fasting had any effects on common markers of metabolic health, inflammation,
etc.
You will not be surprised to learn
that this has been already been done many, many times. This is good, hands-on
research that controls and monitors the subjects’ dietary patterns to be sure
the intervention in question is being fairly assessed. And this research, it turns
out, consistently returns findings that suggest intermittent fasting can
improve common markers of metabolic health, insulin resistance, inflammation,
etc.2–6 Not every trial finds improvements in all the health markers they analyze,
but they very often do. And since I’ve yet to find a fasting intervention that demonstrated
a worsening of chronic health markers, I feel pretty damn confident in saying that
the actual hard science demonstrates a tendency for intermittent fasting to
improve chronic health.
Intermittent Fasting Surveys
So if we wanted the best results possible, we’d
engage in hands-on interventional research. Hard science. But hard science is
costly, labor-intensive, and time-consuming. So for those or other reasons,
maybe we just want to get a peek at what’s happening to those who engage in
intermittent fasting, especially those who have been practicing for a while.
What would we do then? We’d ask them! You could ask people how long they’ve
been practicing intermittent fasting, how often they engage in the practice, how
long their typical eating window is, what foods they typically eat, etc. You’d
also want to ask anything else you could imagine related to their health (exercise,
alcohol, sleep, lifestyle and socioeconomic factors, etc.) to make sure none of
those might influence your results. Then when you have all this data, you could
compare the current health of your subjects to a control group or the general population
to see if you could identify any differences.
This approach is generally weaker
than the interventional trials we described above because they can’t
demonstrate any causal effects, but if done properly there can still be
reasonable value derived from the findings.
“Intermittent Fasting”
Surveys
We’ve covered a couple reasonable
approaches for how we might assess the question at hand if we wanted decent to
good results. But what if we didn’t give a single flying fuck about good
results? What would we do then? What if all we wanted was to attach a soundbite
to a trending health topic? What if we just wanted to manufacture a scary
headline to make it look like not eating for a little bit could literally cause
a heart attack?
Well, we can rule out
interventional trials. We know with great certainty that those won’t work,
because those have repeatedly demonstrated that intermittent fasting is far
more likely to be beneficial than harmful. So we’ll have to go the survey route
instead. But, we probably want to be careful about the questions we ask. If we
ask a bunch of detailed questions that accurately identify subjects deliberately
engaged in the practice of intermittent fasting, we might accidently confirm
the hard science if we end up with people who are healthier than the general population.
So I have an idea. We’ll find
thousands of people and just ask them what they ate yesterday, and when they
ate it. And then later this year we’ll ask them again – what time did you
consume food yesterday? Then we’ll take this sample size of two and categorize anyone
who ate their food in a single eight hour window as someone engaged in “intermittent
fasting,” even if they have no idea what those words even mean. And of course
we’ll pretend this sample size of two accurately reflects their long-term
dietary patterns while we sit around and wait to see who dies over the next
several years.
Deliberating Avoiding Actual
Intermittent Fasting
Hopefully it’s fairly clear that
the sarcastic paragraph above actually just describes the study in question.7 It was two 24 hour dietary recalls in the span of a year, and years of
tracking deaths. The researchers were not seeking out people engaged in regular
intermittent fasting or attempting to understand anybody’s long-term dietary
habits, even though every damn news article includes references to “people who
practice intermittent fasting for long periods of time.”
But why does this produce terrible
results? For the same reasons you can’t draw definitive negative conclusions
from survey data, I actually can’t say definitely. Buuuuuuut I have a pretty
good guess. Take a look at the chart below, which filters the subjects by their
average eating window during those two dietary recalls:
A couple things jump out to me
right away – those that they characterize as engaged in intermittent fasting (8
hour or less eating window) are quite a bit more likely to smoke than the average
person, and are 3 times more likely to be black. This suggests a couple of
things to me. One if that a good number of these people are obviously not actively
seeking the health benefits of intermittent fasting. And the other is that,
unfortunately, this group of subjects is almost certainly at a socioeconomic disadvantage
compares to the others. It remains a regrettable reality in this country that
black Americans are twice as likely to live in poverty and face food scarcity.8,9 Meanwhile, smoking is nearly twice as common below the federal poverty
line as it is above. 10 We don’t literally have it from what the researchers presented, but we
do actually know it – the “intermittent fasting” group is of far lower socioeconomic
status than the others.
I can only think of a couple
reasons someone would engage in deliberate intermittent fasting. Weight loss
and health benefits are the obvious ones. Or maybe that’s really just one
reason. Regardless, people who seek out the deliberate practice fasting are
relatively privileged enough to be doing so.
But let’s reframe it – what are
some reasons a person might skip a meal? Because to a large extent that’s what
is actually happening here. Even just on its face, I would frankly expect there
to be more people who skip breakfast because they stayed up too late and tried
to maximize every minute of sleep before class or work than there are people
engaged in mindful intermittent fasting. That’s obviously not a healthful
approach to life, but it’s not being accounted for at all. It’s more than just that
though, of course. We know that the “fasting” subjects here are disproportionally
likely to be poor, have poor access to food, and so forth.
Some people in this study probably are health-minded
individuals engaged in intermittent fasting. But quite a number are poor people
who stayed up late working their second job and didn’t eat breakfast in the morning.
Or skipped breakfast those two days to save a couple bucks. Or are among the millions
of highly food-insecure Americans who can’t find dinner tonight.
Maybe that’s being too dramatic, I
really don’t know for sure. But I know with certainty that actual hands-on
science tends to show the health benefits of intermittent fasting. And I know
with certainty that these researchers made zero effort to find people engaged
in intermittent fasting. And I know with certainty that the cohort they found
to represent “intermittent fasting” is much more likely to be impoverished and
hungry than the general population.
What I don’t know, as someone in a
position fortunate enough to engage in deliberate healthful fasting, is how
much poverty, food scarcity, and who knows what else affects cardiovascular
disease and mortality. Id imagine that the daily stress experienced by the “intermittent
fasting” group explains most or all of the measured increased in CVD mortality.
In fact, it seems that low socioeconomic status itself is associated with CVD
mortality to a far greater degree than this study claims intermittent fasting
to be.11 And basically to a greater degree than any dietary habit. Perhaps the
AHA might focus on that relationship, if they aspire to a reduction in CVD
deaths.
Conclusion
So that about sums it up. We know,
from legitimate science, that intermittent fasting tends to impart positive
health effects. We also know that these researchers took the about the shittiest
approach they could to studying “intermittent fasting,” and I really have no
problem accusing them of doing it deliberately. And I have no problem noting that
this terrible research being spammed all over the internet, which has not yet even
been fully published or peer-reviewed, just happens to once again align with
the American Heart Association’s persistent opposition to healthful dietary
habits. And while we’re at it, I have no problem suggesting that a lot of what
I just wrote about should probably be absorbed as social/political commentary,
even if it started as a defense of healthy eating habits.
But the bottom line is this – intermittent
fasting is unequivocally not going to induce heart disease.
1. The
intermittent fasting trend may pose risks to your heart. Accessed March 20,
2024.
https://www.msn.com/en-us/health/other/the-intermittent-fasting-trend-may-pose-risks-to-your-heart/ar-BB1k7bsm
2. Gu L, Fu R, Hong
J, Ni H, Yu K, Lou H. Effects of Intermittent Fasting in Human Compared to a
Non-intervention Diet and Caloric Restriction: A Meta-Analysis of Randomized
Controlled Trials. Front Nutr. 2022;9. doi:10.3389/fnut.2022.871682
3. Ahmed N, Farooq
J, Siddiqi HS, et al. Impact of Intermittent Fasting on Lipid Profile–A
Quasi-Randomized Clinical Trial. Front Nutr. 2021;7.
doi:10.3389/fnut.2020.596787
4. Yuan X, Wang J,
Yang S, et al. Effect of Intermittent Fasting Diet on Glucose and Lipid
Metabolism and Insulin Resistance in Patients with Impaired Glucose and Lipid
Metabolism: A Systematic Review and Meta-Analysis. International Journal of
Endocrinology. 2022;2022:e6999907. doi:10.1155/2022/6999907
5. Wang X, Yang Q,
Liao Q, et al. Effects of intermittent fasting diets on plasma concentrations
of inflammatory biomarkers: A systematic review and meta-analysis of randomized
controlled trials. Nutrition. 2020;79-80:110974.
doi:10.1016/j.nut.2020.110974
6. Cho Y, Hong N,
Kim K won, et al. The Effectiveness of Intermittent Fasting to Reduce Body Mass
Index and Glucose Metabolism: A Systematic Review and Meta-Analysis. Journal
of Clinical Medicine. 2019;8(10):1645. doi:10.3390/jcm8101645
7. Chen M, Xu L,
Horn LV, et al. Association of 8-Hour Time-Restricted Eating with All-Cause and
Cause-Specific Mortality.
8. Poverty in the
United States: 2022. Accessed March 20, 2024.
https://www.census.gov/library/publications/2023/demo/p60-280.html
9. Nearly Half of
Black and Hispanic People in the U.S. Face Food Insecurity, New Study Finds |
Johns Hopkins | Bloomberg School of Public Health. Published February 26, 2021.
Accessed March 20, 2024.
https://publichealth.jhu.edu/2021/nearly-half-of-black-and-hispanic-people-in-the-us-face-food-insecurity-new-study-finds
10. Garrett BE.
Socioeconomic Differences in Cigarette Smoking Among Sociodemographic Groups. Prev
Chronic Dis. 2019;16. doi:10.5888/pcd16.180553
11. Zhang YB, Chen C,
Pan XF, et al. Associations of healthy lifestyle and socioeconomic status with
mortality and incident cardiovascular disease: two prospective cohort studies. BMJ.
2021;373:n604. doi:10.1136/bmj.n604
