Intermittent fasting of 16 hours doubles risk of dying from heart disease, says new study: Experts explain the risks

What is time restricted eating?

There is no specific definition for intermittent fasting. People practice it in different ways — consuming meals either in an eight, 10 or 12-hour window every day and fasting for the rest.

What does the current study say?

The recent study found that people who ate for less than eight hours a day had a 135 per cent higher risk of cardiovascular mortality — death due to heart and blood vessel diseases such as heart attacks or strokes — as compared to those who ate for 12 to 14 hours a day. The findings are based on the data of 19,000 adults from the US National Health and Nutrition Examination Survey (NHANES).

The study also looked at links of this intermittent fasting to cancer and all-cause mortality. The researchers found that there was no link to cancer or all-cause mortality. The links with cardiovascular diseases, however, remained even when the results were analysed according to eight different sub-groups such as according to race, ethnicity, or other socioeconomic factors.

“Although (there could be confounding factors), people should be extremely cautious to adopt a short eating window for a long time over years to pursue cardiovascular health or longevity, which has no evidence support from human studies to date,” said Victor Wenze Zhong, a senior author of the study.

What are caveats?

However, the report is also accompanied by an analytical editorial of the pros and cons of the research by Dr Anoop Misra, chairman, endocrinology, Fortis C -DOC. “Intermittent fasting is a promising tool in our dietary arsenal and low cost and simple too, but enthusiasm should be tempered with careful risk assessment. Until more long-term data are available, especially on hard outcomes like cardiovascular events (e.g. heart attacks), intermittent fasting should be individualized and ideally supervised, particularly for people with pre-existing health conditions, and applied for short-term only,” says Dr Misra.

How severe IF affects the heart

According to Dr Ranjan Shetty, lead cardiologist at Sparsh Hospital, Bengaluru, this is not the first such study. A retrospective study by the American Heart Association conference in March 2024 had also claimed that a 16-hour intermittent fasting was linked to a 91 per cent higher risk of death from heart disease. “The problem with the latest study is that it is not a randomised trial. We do not know the base health condition of the participants, their weight and other underlying risk factors,” he says.

However, he cautions that the less than eight-hour eating window or the16-hour fasting format is not suitable for those with arrhythmia. “Severely restricting calories can lower blood sugar levels, which can cause heart palpitations and elevate the heart rate, triggering a heart attack. If you’re not eating enough but go about your regular activities, then your body has to work harder to pump the blood,” he says.

Dr Shetty also feels that the degree of weight loss required needs to be assessed. “If a person is obese, then the weight drop will still settle at an acceptable limit. It may not be the same for another person who is not that overweight. What you have to watch out for is loss of lean muscle mass. Intermuscular fat is bad news for the heart,” he adds.

In fact, he further points out, the study nowhere says the kind of food that the subjects have. “Your cholesterol and fat profile will still go awry if you have high fat, high sugar and high sodium food or junk food even in a time-restricted window,” says Dr Shetty. He doesn’t recommend intermittent fasting for the elderly, children, people with diabetes, chronic conditions impacting their heart, kidney and liver, heart disease and those suffering from an eating disorder. “Above all everybody’s body needs bespoke attention and you need to consult your doctor before going through a fasting regime.”