Should You Try Intermittent Fasting? It Could Improve These 8 Conditions, an Expert Doctor Says

Updated: Jun. 21, 2024

A longtime fasting researcher says a recent American Heart Association's widely touted study may be misleading for certain groups.

Data have shown that intermittent fasting, also called time-restricted eating (TRE), can be a highly reliable way for some people to lose weight that also comes with complementary health benefits. For example, one October 2023 study suggested that eating within an eight-hour window was shown to help people with type-2 diabetes lose more weight than calorie counting alone. In a November 2023 study, a 14-hour fast, or a 10-hour eating window, improved mood, reduced hunger, and enhanced sleep. 

However, a recent study on purported cardiovascular effects of fasting was presented at the American Heart Association’s Epidemiology and Prevention Lifestyle and Cardiometabolic Scientific Sessions 2024, held in Chicago between March 18 to 21. An analysis of more than 20,000 participants with an average age of 49 revealed that those who consumed most of their food within an eight-hour window had a 91% higher risk of dying from cardiovascular disease. Additionally, fasting didn’t reduce the risk of death from any cause compared to eating within a more typical 12- to 16-hour window.

Victor Wenze Zhong, PhD, the lead author of the study and chair of the Department of Epidemiology and Biostatistics at the Shanghai Jiao Tong University School of Medicine in China, stated: “We were surprised to find that people who followed an 8-hour, time-restricted eating schedule were more likely to die from cardiovascular disease. 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.”

One caveat was that people living with cancer showed the greatest benefits and lower death rates with a 16-hour eating window. Dr. Zhong commented, “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.”

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Dr. Zhong emphasized that while the study’s broader findings sound stark, they don’t actually indicate that intermittent fasting causes death. His research team also acknowledged that further research is necessary because the study had some limitations. 

Dr. Mindy Pelz is a functional medicine practitioner, bestselling author of books such as Fast Like a Girl, and a longtime fasting researcher who is calling some of those limitations out. We spoke with Dr. Pelz, who highlighted: “Correlation is not causation … In other words, all this study says is that there’s some link between fasting and heart disease. It doesn’t say why that link exists, or prove any cause-and-effect relationship.”

So, why would that link exist? “A possible explanation is that people with higher heart disease risk are more likely to try fasting,” Dr. Pelz says.

In a March 23, 2024 Instagram post, she added that Dr. Zhong’s team’s research “isn’t a peer-reviewed journal study—it has not been vetted for being an acceptable study.”

Furthermore, Dr. Pelz stresses that 27% of study participants were smokers. “[Smoking] seems like a little more of a cardiovascular problem” compared to fasting, she said.

She reinforces a limitation that Dr. Zhong and his team had stated: that they’d only asked for participants to fill out a questionnaire two days out of the year, not to report their eating habits reflectively, or in realtime. “They didn’t even ask them what they were eating,” Dr. Pelz said. “It’s what you eat and it’s when you eat—both of those matter for your health.”

She notes that the researchers didn’t take into consideration age and demographics and other aspects that play a huge part in health.

Dr. Pelz cites other experimental research, which does have better chance of establishing cause and effect. This research shows that heart health may benefit from fasting:

“In a 2018 study,” Dr. Pelz says, “men with prediabetes did either 18-hour fasting or normal eating every day for five weeks. The study found that fasting significantly improved both cardiovascular and metabolic health—including blood pressure, insulin sensitivity, vascular inflammation, and appetite regulation—and that the benefits occurred even in subjects who didn’t lose weight. That means fasting itself caused the benefits; they weren’t a side effect of weight loss.”

She also cited the following research:

“A 2020 study had people with metabolic syndrome fast 14 hours a day for 12 weeks. Participants showed a significant improvement in cardiovascular health, including decreased blood pressure and atherogenic blood lipids. 

A 2014 study found that several kinds of fasting all decreased cardiovascular risk and helped participants lose weight.  

A 2020 review covers close to a dozen other studies showing that fasting decreases risk of cardiovascular disease. 

Based on all the other research, it’s very unlikely that fasting doubles heart disease risk.”

Dr. Pelz offers the following conditions as those “who might be drawn to fasting, after seeing all that beneficial coverage on how good it is for your health”:

  • Overweight people
  • People with high blood pressure
  • Older people whose doctors have told them they need to change their diet
  • People with chronic inflammation
  • People with diabetes, prediabetes, metabolic syndrome, or insulin resistance

While the AHA study suggested potential long-term negative effects of certain timeframes of restricted eating, Dr. Zhong emphasized that this isn’t universally true. “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 said. 

In any case, research consistently suggests that obesity is associated with other illnesses that can impact longevity. Also, any individual’s diet should be determined by their licensed healthcare provider.