A new study raises a cautionary note on time-restricted eating (TRE), a type of intermittent fasting that is gaining popularity.
The observational analysis of over 20,000 US adults showed that those who limited their eating to a period of less than 8 hours per day had a higher risk for cardiovascular mortality compared with peers who ate across the typical 12-16 hours per day. This was the case in the overall sample and in those with cardiovascular disease (CVD) or cancer.
Lead author Victor Wenze Zhong, PhD, cautioned that the findings “require replication and we cannot demonstrate 8-hour TRE causes cardiovascular death in this observational study.”
“However, it’s important for patients, particularly those with existing heart conditions or cancer, to be aware of the positive association between an 8-hour eating window and cardiovascular death,” Zhong, professor and chair, Department of Epidemiology and Biostatistics, School of Public Health, Shanghai Jiao Tong University School of Medicine, Shanghai, China, told theheart.org | Medscape Cardiology.
The results (Abstract P192) were presented March 18 at the American Heart Association (AHA) Epidemiology and Prevention | Lifestyle and Cardiometabolic Health Scientific Sessions 2024.
‘Provocative’ Results
Short-term randomized controlled trials have suggested that 8-hour TRE may improve cardiometabolic risk profiles, but the potential long-term effects of this eating pattern are unknown.
The observation that TRE may have short-term benefits but long-term adverse effects is “interesting and provocative” and needs further study, Christopher D. Gardner, PhD, professor of medicine at Stanford University in California, who wasn’t involved in the study, said in a conference statement, and he agreed that much more research is needed.
The researchers analyzed data on dietary patterns for 20,078 adults (mean age, 48 years; 50% men; 73% non-Hispanic White) who participated in the 2003-2018 National Health and Nutrition Examination Surveys (NHANES). All of them completed two 24-hour dietary recall questionnaires within the first year of enrollment. Deaths through the end of 2019 were determined via the National Death Index.
During a median follow-up of 8 years, there were 2797 deaths due to any cause, including 840 CV deaths and 643 cancer deaths.
In the overall sample, compared with an eating duration of 12-16 hours, 8-hour TRE was significantly associated with an increased risk for CV mortality (hazard ratio [HR], 1.91; 95% CI, 1.20-3.03).
This association was also observed in adults with CVD (HR, 2.07; 95% CI, 1.14-3.78) and adults with cancer (HR, 3.04; 95% CI, 1.44-6.41).
Other eating durations were not associated with CV mortality, except for eating duration of 8 to less than 10 hours in people with CVD (HR, 1.66; 95% CI, 1.03-2.67).
No significant associations were found between eating duration and all-cause or cancer mortality in the overall sample and CVD/cancer subsamples, except that eating duration of more than 16 hours was associated with a lower risk for cancer mortality in people with cancer (HR, 0.47; 95% CI, 0.23-0.95).
Quality More Important Than Timing
Zhong noted that the study doesn’t address the underlying mechanisms driving the observed association between 8-hour TRE and CV death.
“However, we did observe that people who restricted eating to a period less than 8 hours per day had less lean muscle mass compared with those with typical eating duration of 12-16 hours. Loss of lean body mass has been linked to higher risk of cardiovascular mortality,” Zhong said.
“Based on the evidence as of now, focusing on what people eat appears to be more important than focusing on the time when they eat. There are certain dietary approaches with compelling health benefits to choose, such as DASH diet and Mediterranean diet,” Zhong told theheart.org | Medscape Cardiology.
Intermittent fasting is “certainly an interesting concept and one on which the potential mechanisms underlying the improvements in short outcome studies and preclinical studies in animals are strongly being pursued,” Sean Heffron, MD, cardiologist at the Center for the Prevention of Cardiovascular Disease at NYU Langone Heart, New York, NY, who wasn’t involved in the study, told theheart.org | Medscape Cardiology.
Heffron expressed skepticism about the study results calling them “far from complete” and noted that data on diet was based on only 2-day diet records without correction for confounding variables.
Heffron also noted that the restricted diet group has more smokers and more men. “I would “strongly anticipate that once appropriate corrections are made, the findings will no longer persist in statistical significance,” Heffron said.
He emphasized the need for more rigorous research before making clinical recommendations. When patients ask about intermittent fasting, Heffron said he tells them, “If it works for you, that’s fine,” but he doesn’t provide a recommendation for or against it.