Medical experts on Friday urged caution with intermittent fasting after two studies reinforced evidence that the regimen can improve blood sugar while also more than doubling the risk of premature cardiovascular death.
A study analysing data from over 19,800 adults in the US found that those who compressed all their eating into less than eight hours and fasted the remaining 16 hours had a 2.35-fold higher mortality risk compared with those with typical 12–14 hour eating windows.
The findings bolster evidence for risks linked to intermittent fasting — a practice of finishing the day’s last meal by 6pm and fasting 14 to 16 hours or longer — even as other independent studies have highlighted its benefits for blood sugar control.
People should be “extremely cautious” about maintaining a short eating window over a long period, said Victor Wenze Zhong, a professor of epidemiology at the Shanghai Jiao Tong University School of Medicine in China who led the new US-China study.
The study’s findings were published in the journal Diabetes and Metabolic Syndrome: Clinical Research and Reviews on Friday.
“These results are highly relevant to India, where intermittent fasting is becoming popular without medical supervision or without regular health checkups,” said Anoop Misra, chairman of the Fortis Centre for Diabetes, Obesity and Cholesterol, New Delhi.
“The implications could be even more serious for Indians given their higher susceptibility to heart disease,” Misra told The Telegraph.
The second study — a comprehensive review of earlier research — has underscored the promise of intermittent fasting in blood sugar management for people with diabetes and suggested it could be incorporated into dietary recommendations prescribed for diabetes or obesity.
Multiple earlier studies have shown that intermittent fasting can also support weight loss, improve insulin sensitivity, reduce blood pressure, enhance cholesterol levels, and aid blood sugar control without strict calorie counting.
Potential downsides, however, include nutrient deficiencies, excessive hunger, irritability, headaches, and, for people with diabetes, episodes of hypoglycemia or low blood sugar.
The US-China study now adds cardiovascular risk to these concerns, said Misra.
“Intermittent fasting appears to be a low-cost, simple, and promising tool in our dietary arsenal, but enthusiasm should be tempered with caution,” Misra said. “Until long-term data on events such as heart attacks are available, intermittent fasting should be individualised and supervised, particularly for people with pre-existing conditions.”
Medical interest in intermittent fasting emerged in the mid-2000s when small studies in adults suggested that restricting meals to specific hours could improve fasting glucose and insulin sensitivity. Larger trials and reviews in the 2010s reinforced those findings and have helped popularise the practice.
Researchers say the biological reasons for the higher cardiovascular death risk remain uncertain. Possible explanations include nutrient deficiencies, disruption of bio clock rhythms, and overeating during the eating periods. In people with diabetes, intermittent fasting may also trigger dangerous swings in blood sugar.