22/03/2024
Let's talk about a new study that claims that intermittent fasting increases the risk of cardiovascular death 91%
👇🏾👇🏾👇🏾
Let's talk about a new study that claims that intermittent fasting increases the risk of cardiovascular death.
Two days ago, one of my clients called my attention to an Instagram post by People Magazine. The post was about a new study that claims Intermittent Fasting/Time-restricted eating increases the risk of cardiovascular death by 91%. It was a sensational headline, and the pro-IF and anti-IF groups were having a day in the comments section.
Because that was the first time I heard about the new study, I clicked the link attached to the post to read the paper. To my disappointment, the study has not been published yet because it's still being peer-reviewed. The press release is available, so I read the press release.
Let's take a look at some key points from the press release:
*Type of Study*
It's a retrospective study that reviewed information about dietary patterns for participants in the annual 2003-2018 National Health and Nutrition Examination Surveys (NHANES) in comparison to data about people who died in the U.S., from 2003 through December 2019, from the Centers for Disease Control and Prevention’s National Death Index database.
*A retrospective study* is a study that uses data that has already been recorded for other reasons. It compares two groups of people, one with a disease or condition and one without, and studies each group's medical and lifestyle histories to learn what factors may be associated with the condition.
*The study used the 24-hour dietary recall data from the National Health and Nutrition Examination Surveys (NHANES).* I emphasised the sentence because the NHANES collect 100s and 100s of health and lifestyle data from survey participants. However, the authors of this yet-to-be-published study chose a single data point. I'll come back to why this is wrong later. But for now, let me explain what a 24-hour dietary recall is.
*A 24-hour dietary recall* is a method that monitors and assesses the food and drink consumption of an individual during the previous day.
What's wrong with the study
As I mentioned earlier, this is a retrospective study (I hope you still remember the definition of a retrospective study). The authors of this study took a single data (24-hour food recall) from a health survey database and concluded that everyone who died of a cardiovascular disease likely died because they were practising IF/TRE.
As I pointed out before, the National Health and Nutrition Examination Surveys (NHANES) have 100s and 100s of health-related data of the thousands of people participating in the programme. So, if a researcher wants to know if eating an apple a day keeps the doctor away, she can go into the NHANES database and extract any data she wants to use for her study. Because the NHANES is a large database, the researcher has a large sample size to work with. In the case of the authors of the new study, they had 20,000 people from the NHANES and maybe another 20,000 people from the CDC.
It doesn’t make sense that the authors of the new study chose to use only the 24-hour food recall data that was collected in 2003 when they had access to other health data.
How can you suggest or claim that IF/TRE is causal when you did not adjust for other factors like existing medical conditions, smoking, stress level, and other lifestyle factors? To drive home my point, here’s an excerpt from the press release:
“The study’s limitations included its reliance on *self-reported dietary information, which may be affected by participant’s memory or recall and may not accurately assess typical eating patterns. *_Factors that may also play a role in health, outside of the daily duration of eating and cause of death, were not_* included in the analysis*“ (Emphasis mine)
*Let's do a little exercise:*
I want you to recall and write everything you ate and drank in the last 24 hours. While you're at it, write down the time you ate and drank those things. Write down the portion and size of each food and drink. Be very thorough. Now, go over your list and see if you left anything out. Do that again one or two more times. Are you satisfied with your list? Good!
Look at the time of the day you ate and drank again, did you recall the window of time for eating correctly? Does the window of time for eating represent your typical pattern of eating? I hope so because we'll come back in 2039 and hold your window of time for eating on March 21, 2024, responsible for your health outcome.
If you just wondered about the absurdity of my reasoning, maybe you should do the same with the study.
“The study’s limitations included its reliance on *self-reported dietary information, which may be affected by participant’s memory or recall and may not accurately assess typical eating patterns. Factors that may also play a role in health, outside of the daily duration of eating and cause of death, were not* included in the analysis“
*91% of What?*
The most disappointing part of this whole thing is how the American Heart Association sensationalised the press release. Look at the headline for the press release:
*8-hour time-restricted eating linked to a 91% higher risk of cardiovascular death*
Yep! That's the exact headline from the American Heart Association press release.
It's one thing for the mainstream media to sensationalise a study like this, but it's disappointing for an organisation like the American Heart Association to use such a headline.
Let's go beyond sensationalism and dive into what the 91% means.
*What does the 91% in the study mean?*
When you see a headline that says, “91% increased risk”, you may think it means 91% of those who do IF/TRE are likely to die from cardiovascular disease. That's more than 9 out of every 10 people. If that's how you understood the headline, that would send a chill down your spine, and you would wish you had never done Intermittent Fasting/TRE a single day in your life.
Any factor that increases the risk of death by 91% is some scary stuff. Even the most deadly form of cancer doesn't have that extremely high mortality rate.
*What type of risk?*
When you read risk percentage in health studies, it refers to either absolute risk (AR) or relative risk (RR).
*Absolute risk explained:* Absolute risk refers to the actual likelihood of an event or outcome occurring within a certain population over a specific period. It represents the raw or actual number of individuals who experience a particular outcome, without comparing it to another group. For example, if 100 out of 1000 people develop a disease, the absolute risk of developing that disease is 100 out of 1000, or 10%. It provides a straightforward understanding of the probability of an event occurring within a defined population.
*Relative risk explained:* Relative risk is a measure used in epidemiology and medical research to compare the risk of a certain outcome (such as developing a disease) between different groups. It's calculated by dividing the risk of the outcome in one group by the risk of the outcome in another group.
*Here's an example:*
Let's say you're conducting a study to determine the risk of developing heart disease among smokers compared to non-smokers.
- Number of smokers who developed heart disease = 100
- Number of smokers who didn't develop heart disease = 200
- Number of non-smokers who developed heart disease = 50
- Number of non-smokers who didn't develop heart disease = 300
Relative risk (RR) is calculated as the ratio of the risk of developing heart disease in the exposed group (smokers) to the risk in the unexposed group (non-smokers).
So, RR = (Risk of heart disease in smokers) / (Risk of heart disease in non-smokers)
RR = (100/300) / (50/350)
= (1/3) / (1/7)
= (1/3) * (7/1)
= 7/3
≈ 2.33
Therefore, the relative risk of developing heart disease among smokers compared to non-smokers is approximately 2.33. This means that smokers are about 2.33 times more likely to develop heart disease compared to non-smokers.
If we want to express the 2.33 relative risk as a percentage, we'll say, smoking increases heart disease risk by 133%.
So, what does the 91% increased risk mean?
The 91% increased risk in the study refers to relative risk (RR).
A relative risk of 91% indicates that the exposed group (the IF/TRE group) is 91% more likely to die from cardiovascular disease compared to the unexposed group (the 12-16 eating group).
Relative Risk = (Deaths from cardiovascular diseases in the IF/TRE group) / (Deaths from cardiovascular disease in the 12-16 hours feeding group) = 1.91
That means for every 10 cardiovascular deaths in the 12-16 hours feeding group, there were 19.1 (about 20) in the IF/TRE group.
Therefore, 91% or 1.91 RR means that, compared to those who eat within a 12-16-hour window, those who do 8 hours or less are nearly twice as likely to die from cardiovascular disease.
*Is 1.91 RR high risk?*
In epidemiology, the interpretation of relative risk values can vary depending on the context and specific guidelines used. However, relative risks are often categorised as follows:
RR < 1: Indicates a decreased risk in the exposed group compared to the unexposed group.
RR = 1: Indicates no difference in risk between the exposed and unexposed groups.
1 < RR < 2: Indicates a moderately elevated risk.
RR ≥ 2: Indicates a high risk.
Since a relative risk of 1.91 falls between 1 and 2, it'll be considered moderately elevated, suggesting that the IF/TRE group has a moderately higher risk of dying from cardiovascular disease.
The factors that were not adjusted or accounted for in the study
As stated in the press release, the study didn't adjust for other risk factors. Look again at this excerpt from the press release:
“The study’s limitations included its reliance on self-reported dietary information, which may be affected by participant’s memory or recall and may not accurately assess typical eating patterns. Factors that may also play a role in health, outside of the daily duration of eating and cause of death, were not included in the analysis“
While we wait for the publication of the complete study, I'll end this article with another excerpt from the press release. Read it carefully and then decide for yourself if the sensationalisation of a study that's not yet published is worth losing sleep over:
——
“When the study is presented in its entirety, it will be interesting and helpful to learn more of the details of the analysis, said Christopher D. Gardner, Ph.D., FAHA, the Rehnborg Farquhar Professor of Medicine at Stanford University in Stanford, California, and chair of the writing committee for the Association’s 2023 scientific statement, Popular Dietary Patterns: Alignment with American Heart Association 2021 Dietary Guidance.
One of those details involves the nutrient quality of the diets typical of the different subsets of participants. Without this information, it cannot be determined if nutrient density might be an alternate explanation to the findings that currently focus on the window of time for eating. Second, it needs to be emphasized that categorization into the different windows of time-restricted eating was determined on the basis of just two days of dietary intake,” he said.
"It will also be critical to see a comparison of demographics and baseline characteristics across the groups that were classified into the different time-restricted eating windows – for example, was the group with the shortest time-restricted eating window unique compared to people who followed other eating schedules, in terms of weight, stress, traditional cardiometabolic risk factors or other factors associated with adverse cardiovascular outcomes? This additional information will help to better understand the potential independent contribution of the short time-restricted eating pattern reported in this interesting and provocative abstract.”
—–
I hope you found this article helpful.
