The new study suggest a potentially alarming correlation: consuming meals within an eight-hour window or less may be linked to a striking 91% higher risk of cardiovascular disease-related mortality
Intermittent fasting is a form of time-restricted eating that may aid in weight loss, fat loss, and reducing the risk of conditions like type 2 diabetes and heart disease. (Shutterstock)
Intermittent fasting has emerged as a popular approach among individuals seeking to manage their weight. It is a form of time-restricted eating that may aid in weight loss, fat loss, and reduce the risk of conditions like type-2 diabetes and heart disease.
Particularly, the 16:8 method, has gained popularity for weight management. This approach involves fasting for 16 hours daily and consuming all calories within an eight-hour window.
The method allows flexibility in food choices but emphasises the importance of consuming nutritious foods like fruits, vegetables, whole grains, lean proteins, and healthy fats.
“With rising rates of obesity around the world, people are resorting to various methods to bring their body weight down. One such trend is intermittent fasting, which occurs in various forms. A popular type of intermittent fasting includes spending 16 hours a day without eating and compressing all the day’s meals into the remaining eight hours,” Kochi-based gastroenterologist Dr Rajeev Jayadevan confirmed to South First.
He added that alternate-day fasting is another method, and fasting or reducing food intake for two days a week and maintaining a normal diet for the remaining five was another technique.
“All these in principle are themed on calorie restriction. They are seemingly easier to implement than to go through old-fashioned calorie restriction for seven days a week,” said Jayadevan.
However, recent research findings, unveiled this week, have not only sparked scepticism from experts but also garnered criticism.
These findings suggest a potentially alarming correlation: Consuming meals within a window of eight hours or less may be linked to a striking 91 percent higher risk of cardiovascular disease-related mortality, compared to a more extended eating window of 12-16 hours.
An analysis of over 20,000 US adults found that people who limited their eating across less than eight hours per day — a time-restricted eating plan — were likelier to die from cardiovascular disease compared to people who ate across 12-16 hours per day.
This was according to preliminary research presented at the American Heart Association’s Scientific Sessions 2024.
Time-restricted eating — a type of intermittent fasting — involves limiting the hours for eating to a specific number of hours each day, where a time window may range from four to 12 hours in the 24 hours of a day.
The aforementioned study was conducted at the Shanghai Jiao Tong University School of Medicine in the Shanghai province of China.
In the study, researchers examined data from approximately 20,000 people.
These individuals provided information regarding their 24-hour eating patterns on two separate days within the initial year of enrolment in a comprehensive long-term analysis focusing on the health of US adults.
Subsequently, the researchers retrospectively reviewed death records in the years following this initial data collection period.
The study analysis found that:
In this study, researchers investigated the potential long-term health impact of following an eight-hour time-restricted eating plan.
They 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 US.
The American data ranged from 2003 to December 2019, and was sourced from the Centres for Disease Control and Prevention’s National Death Index database.
“We were surprised to find that people who followed an eight-hour, time-restricted eating schedule were likelier to die from cardiovascular disease,” said senior study author Victor Wenze Zhong, a PhD, a professor, and chair of the Department of Epidemiology and Biostatistics at the Shanghai Jiao Tong University School of Medicine in Shanghai, China, in a statement.
“Even though this type of diet has been popular due to its potential short-term benefits, our research clearly shows that, compared with a typical eating time range of 12-16 hours per day, a shorter eating duration was not associated with living longer,” he noted.
“It’s crucial for patients, particularly those with existing heart conditions or cancer, to be aware of the association between an 8-hour eating window and increased risk of cardiovascular death. Our study’s findings encourage a more cautious, personalized approach to dietary recommendations, ensuring that they are aligned with an individual’s health status and the latest scientific evidence,” he continued. “Although the study identified an association between an 8-hour eating window and cardiovascular death, this does not mean that time-restricted eating caused cardiovascular death.”
The findings have not yet been published in a peer-reviewed journal. Additionally, it is an observational study.
The research involved a large sample size and utilised a longitudinal design, spanning an average of eight years to observe individuals.
However, dietary information was collected through two 24-hour recalls at enrolment, potentially limiting the study’s findings and accuracy, as dietary patterns can change over time.
Moreover, observational studies inherently cannot establish cause-and-effect relationships.
There are huge issues that can confound interpretation of observational studies like the one in question. The most obvious one that comes to mind is whether the time restriction is out of conscious healthy choice or out of financial necessity. Makes a big difference..
— Varun C. MD, DM (@drcheruvarun) March 19, 2024
The American Heart Association wants to end heart disease like Lockheed Martin wants to end all wars
— Suneel Dhand MD (@DrSuneelDhand) March 20, 2024
“This is correlational evidence. This is another way of saying it’s results based on questionnaires conducted over years. It can only establish coincidence, not causality,” said Dr Ben Bikman, a biomedical scientist at Brigham Young University on X.
He noted that these results are unpublished. “This report hasn’t undergone any peer review and we have no idea about confounding variables (likely many) or the study population [sic],” he added.
“Again, these results were presented at a scientific meeting, not in a peer-reviewed journal. For example, what if people who eat in a narrower time window are people who work 16-hour days?[sic]” asked Bilkman.
By now, you’ve likely seen the headlines about the study detailing a 91% increased in heart disease from fasting. To be specific, they found that people who reported eating less than 8 hours in a day, compared to this who reported eating 12-16 hours in a day, had an almost…
— Benjamin Bikman (@BenBikmanPhD) March 20, 2024
Meanwhile, Hyderabad-based neurologist Dr Sudhir Kumar said that the data about the eating window was obtained in only two days.
“If we extrapolate two-day data to eight years or longer, [that] data can not be accurate. What people said was believed. The data was not verified by the study team. It is well known that people often do not correctly recollect the eating window or food details. What people ate during the 8 hours also matter. If they consumed unhealthy food, it would lead to adverse outcomes,” said Dr Sudhir Kumar on X.
He added that this study showed only an association, and hence cause-effect can not be established. “This was a poster presentation in a conference. It has not been peer-reviewed and has not been published in a reputed medical journal,” said Dr Kumar.
He also asked if death was the only outcome worth looking at.
“The answer is no. There are several treatments that improve the quality of life but does not reduce deaths. For example, thrombolysis in acute stroke reduces disability at 90 days after stroke, but does not reduce deaths (as compared to those not thrombolysed). TRE is well-known to reduce the risk of obesity, diabetes and other metabolic disorders. Moreover, this study did not show an overall increase in death in 8-hour TRE group [sic],” said Kumar.
He out pointed that research also needs data regarding other factors that have a relationship with cardiovascular diseases — such as sleep duration, aerobic exercise, strength training, stress, abdominal obesity, blood sugars, BP, cholesterol levels, apolipoprotein levels, family history, age, etc. Various groups should be properly matched for these factors to draw any meaningful conclusion.
“This study is scientifically not sound and should not change our practice regarding intermittent fasting. Intermittent fasting does not increase the overall risk of death (shown in this study). Randomized controlled trials are needed to confirm the association between intermittent fasting and cardiovascular death. Intermittent fasting is safe for people with overweight, obesity, diabetes as well as healthy people. However, it should be done under supervision of doctors and nutritionists,” said Kumar.
Time-restricted eating (TRE) and cardiovascular mortality: Analysis of a recent study
What do the authors of the study claim?
After a median follow up of 8 years, group practicing 8-hour TRE had 91% greater risk of cardiovascular mortality, as compared to those eating during a… pic.twitter.com/2zel72tTTK— Dr Sudhir Kumar MD DM (@hyderabaddoctor) March 20, 2024
Jayadevan said that those considering this research must also acknowledge that the peer-reviewed paper had not been published yet.
“But if the findings are true, this is a red flag for people who choose intermittent fasting as opposed to traditional calorie restrictions to lose weight, improve metabolic parameters and long-term outcomes,” said Jaydevan.
He pointed out that any study would have limitations. In this case, a reverse causality bias was possible because the people who undertook intermittent fasting tended to do it because they had been told to do so by someone who assessed their health parameters.
“In other words, it’s possible that people with chronic health conditions are over-represented in the fasting group compared to those on a regular diet,” he pinpointed.
“This, however, needs to be ascertained from the paper whenever it gets published. In other words, what we need to know is what was the health profile of the two groups of people at baseline before these diet plans were followed, and whether the observed increased mortality was the result of their underlying health condition rather than the fasting. This is a question that will be answered once the paper comes out,” said Jayadevan.
Dr Jayadevan said that the health outcome data about intermittent fasting have been far from promising. In the short term, people have indeed lost weight. But a recent randomised trial comparing intermittent fasting to daily calorie restriction, followed over a year, has shown no difference in metabolic parameters including fasting glucose, and fasting insulin resistance in healthy obese adults.
The trial was published by Trepanowski et al in JAMA in 2017.
“This is more important than observational studies because it was a randomised controlled trial. The authors found that the level of LDL cholesterol paradoxically increased in the intermittent fasting group at the end of the year,” said Jaydevan.
In summary, even though in the short-term people who follow intermittent day fasting tend to lose some weight, the long-term outcomes are unclear.
“Meanwhile, for those who wish to lose weight and improve their metabolic parameters, it is well established that a disciplined, balanced diet themed on calorie restriction under the supervision of a qualified dietician, along with a physically active lifestyle will definitely help,” said Jaydevan.
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