NEW YORK, Sept 1: Intermittent fasting, the popular diet trend that restricts eating to a limited daily window, may increase the risk of cardiovascular disease, according to a new large-scale study. Researchers found that adults who confined their eating to less than eight hours a day had a 135% higher risk of dying from heart-related conditions compared with those who spread meals over 12 to 14 hours.

The study tracked more than 19,000 American adults over eight years, using dietary recalls to estimate participants’ typical eating windows. The elevated cardiovascular risk persisted across age, sex, socioeconomic status, and lifestyle groups, and was strongest among smokers and people with diabetes or pre-existing heart disease.

Lead author Prof. Victor Wenze Zhong, an epidemiologist at Shanghai Jiao Tong University School of Medicine, cautioned that the study does not prove cause and effect but signals a need for careful consideration of time-restricted eating. “The unexpected finding is that sticking to a short eating window of less than eight hours over the years was linked to increased death risk from cardiovascular disease,” he said.

The study found only a weak and inconsistent link between intermittent fasting and overall mortality from all causes. However, the specific risk to heart health raises questions about the long-term safety of narrow eating windows, especially for vulnerable groups.

Intermittent fasting, which often compresses eating into an eight-hour daily window, has been praised for potential benefits including weight loss, improved insulin sensitivity, lower blood pressure, and better lipid profiles. Supporters claim it may help manage blood sugar without calorie counting and fit easily with cultural or religious fasting practices.

But experts warn of potential downsides. Prof. Anoop Misra, a leading endocrinologist, notes that fasting may cause nutrient deficiencies, increased cholesterol, irritability, headaches, and loss of adherence over time. For people with diabetes, unmonitored fasting can trigger dangerous drops in blood sugar, while older adults or those with chronic conditions risk frailty or accelerated muscle loss.

Previous short-term studies showed modest weight loss, with some muscle loss, and side effects including hunger, dehydration, weakness, and difficulty concentrating. The new study adds a more concerning possible link to heart disease, highlighting the need for personalized dietary guidance.

Prof. Zhong recommends that individuals with heart disease or diabetes be cautious about adopting an eight-hour eating window. He advises focusing on what is eaten rather than strictly when it is eaten. “People may consider not adopting an eight-hour eating window for a long time, either for the purpose of preventing cardiovascular disease or for improving longevity,” he said.

For now, the safest approach may be to tailor intermittent fasting to individual health profiles and prioritize the quality of the diet over the timing of meals.