Is Intermittent Fasting Harmful to Your Heart?


New research suggests that people who practice time-restricted eating, where they only eat during an eight-hour period each day, might have a higher risk of dying from heart disease compared to those who eat during a more typical 12 to 16-hour window. This was found in a study presented at an American Heart Association conference in Chicago. Victor Wenze Zhong, a professor at Shanghai Jiao Tong University School of Medicine, who led the study, expressed surprise at these results.

The study’s findings are interesting, but it’s important to remember that this type of study can only show a link between things, not cause and effect.

Christopher D. Gardner, a nutrition expert from Stanford University, raises some questions about the study. He wants to know more about what foods people were eating. Since the study hasn’t been reviewed by other scientists yet, we don’t have all the details.

Gardner also thinks that focusing on when you eat might not be as important as focusing on what you eat. As a nutrition scientist, he believes that the quality of food matters more than the timing of meals.

Benefits of Time-Restricted Eating

Earlier studies have shown that eating only during certain hours of the day, known as time-restricted eating, can help improve heart health in the short term. This means people only eat during a set time period each day, which could be as short as 4 hours or as long as 12 hours.

For example, some people might fast for 16 hours and then eat all their meals within an 8-hour window, like from 7 a.m. to 3 p.m. or 11 a.m. to 7 p.m.

Past research, which usually lasted one month to one year, found that time-restricted eating can improve blood pressure, blood sugar, cholesterol levels, and weight management.

Findings from a Study on Time-Restricted Eating

The New Study Followed 20,000 Adults for a Median of 8 Years

A recent study looked at information from about 20,000 adults in the United States. These adults were part of the National Health and Nutrition Examination Surveys from 2003 to 2018. The study lasted for about 8 years on average, with some people being followed for up to 17 years.

Participants were asked to remember what they ate in the past day using two questionnaires when they first joined the study. Then, researchers divided them into groups based on how long they ate each day. Some people had eating windows of less than 8 hours, while others had windows of 12 to 16 hours.

The researchers checked back with the participants over the years to see how they were doing health-wise. After looking at many factors like age, race, and health history, the researchers found that:

  • People who ate in less than an 8-hour window had a 91 percent higher risk of dying from heart-related issues, like heart disease and stroke, compared to those who ate in a 12 to 16-hour window.
  • For people with heart disease already, eating within an 8 to 10-hour window was linked to a 66 percent higher risk of dying from heart-related problems.
  • However, time-restricted eating didn’t lower the overall risk of death from any cause.

Study Has Limitations That May Question the Findings

Experts in nutrition who reviewed the new study mentioned some issues with how the research was done that might make the results less reliable.

Krista Varady, a professor at the University of Illinois in Chicago, thinks the conclusions are too strong because the researchers only collected data on what people ate for two days over a 20-year period. She wonders what the participants were eating on the other 7,300 days of the study. Varady has studied intermittent fasting for weight loss and health improvement but wasn’t part of this study.

Christopher Gardner, a professor at Stanford University, also sees a problem with how the study grouped people based on just two days of diet information. He thinks it would have been better to collect data for several days in the first year and then continue gathering information in the following years.

Dr. Zhong, who led the study, agrees that this is a limitation. However, he mentions that they excluded people who reported unusual diets on those two days.

Study Limitations and Possible Influencing Factors

Other things could have affected the risk of heart disease among the people in the study, according to Gardner. For instance, those who ate in a shorter time period might have had less access to food, worked more shifts, or had more stress in their lives compared to those who ate in a longer time period. If this were the case, the higher risk of heart disease-related deaths might not be because of the shorter eating window, but because of these other factors.

Need for Further Research on Time-Restricted Eating

Researchers agree that more studies on time-restricted eating are necessary. Victor Zhong, one of the researchers, believes caution should be taken when following this eating pattern for a long time. He suggests focusing on diets like DASH and Mediterranean, which have proven health benefits. Christopher Gardner shares this view and adds that while time-restricted eating may help some people psychologically, it’s essential to consider the overall quality of one’s diet. Many find it challenging to make healthy choices in today’s food environment, where unhealthy options are cheap, readily available, and appealing.

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