Intermittent fasting has become a popular diet trend in recent years for weight loss. The idea is simple, you focus on when you eat, not what you eat. Many tech leaders, Hollywood stars, and even politicians like Britain’s former Prime Minister Rishi Sunak, who reportedly starts his week with a 36-hour fast, follow this method. Research has often suggested benefits. Extending the overnight fast may help metabolism, support cell repair, and even improve longevity. But experts warn that skipping meals isn’t a one-size-fits-all solution and may be risky for those with existing health conditions.
How intermittent fasting works
Intermittent fasting usually involves eating within a short daily window, often eight hours, leaving a 16-hour fasting period. Other methods, like the 5:2 diet, restrict calories on certain days instead of hours.
New study raises heart health concerns
Now, a large new study raises an important warning. Researchers analysed data from more than 19,000 adults and found that people who ate within an eight-hour window or less faced a 135 per cent higher risk of dying from cardiovascular disease, problems affecting the heart and blood vessels, compared to those who spread their meals over 12 to 14 hours.
Cardiovascular risk means a higher chance of serious heart problems, like heart attacks or strokes. The study found that while intermittent fasting didn’t strongly affect overall deaths, the risk of heart-related deaths was consistently higher across all ages, genders, and lifestyles. In short, eating in a very short time window may not change overall life expectancy much, but it could significantly raise the risk of heart problems.
How the study was conducted
The study tracked American adults over eight years. Participants recalled everything they ate and drank on two separate days, about two weeks apart. Researchers used these records to estimate each person’s usual eating window. People who confined their meals to eight hours or less had higher heart-related risks than those who ate over 12–14 hours. The risk was particularly high for smokers, people with diabetes, and those with existing heart conditions. It remained even after adjusting for diet quality, meal frequency, and other lifestyle habits.
Victor Wenze Zhong, the lead author of the study published in Diabetes and Metabolic Syndrome: Clinical Research and Reviews, said, “The unexpected finding is that sticking to a short eating window for years was linked to increased death risk from cardiovascular disease.” Zhong, an epidemiologist at Shanghai Jiao Tong University School of Medicine, adds that this challenges the belief, based on short-term studies, that intermittent fasting improves heart health.
Benefits and risks of intermittent fasting
Anoop Misra, a top endocrinologist, says intermittent fasting does have some benefits. It can help with weight loss, improve blood sugar control, lower blood pressure, and improve cholesterol. Some studies also suggest it may reduce inflammation. Fasting is simple to follow and can fit with religious or cultural practices.
But Misra also warns of potential negative effects. Fasting may cause nutrient deficiencies, higher cholesterol, strong hunger, irritability, headaches, and difficulty keeping up the routine. People with diabetes who fast without monitoring risk dangerous drops in blood sugar. Older adults or those with long-term health conditions could lose muscle or become frail.
Intermittent fasting has faced criticism before. A 2020 study in JAMA Internal Medicine over three months showed only small weight loss, mostly from muscle. It further stated side effects like weakness, dehydration, headaches, and trouble concentrating. The latest study adds another concern, a possible higher risk of heart problems, especially for certain groups.
Expert Advice: Personalised approach is key
When asked what people and doctors should take away, Prof Zhong said those with diabetes or heart problems should be careful about adopting an eight-hour eating window. “Personalized advice based on health and ongoing research is essential,” he said.
He explained, “Right now, focusing on what you eat may be more important than when you eat. People may consider avoiding an eight-hour eating window long-term if they want to protect heart health or improve longevity.”
The key takeaway is not to abandon intermittent fasting completely but to adapt it as per individual health needs. Until more research is available, experts suggest paying more attention to the quality of food rather than strictly limiting the eating window. Intermittent fasting may still have benefits, but it’s not risk-free. People should consult their doctor before starting any strict fasting plan, especially if they have heart disease, diabetes, or other health concerns.