Intermittent fasting may harm heart health, warns major new study

New research links short 8-hour eating windows to higher risk of cardiovascular death, raising questions over the long-term effect of intermittent fasting for heart health

Fasting regularly to stay fit? You’re not the only one. From Silicon Valley techies to Bollywood celebrities, intermittent fasting has become the go-to wellness trend. It promises fat loss, better metabolism, and sharper thinking. But a recent study suggests it might be harming you, especially for your heart.

 

A latest study titled 'Intermittent fasting: Evidence for benefit, lack of effect, or potential cardiometabolic risk?', published in the journal Diabetes and Metabolic Syndrome: Clinical Research and Reviews, found that people who ate all their meals within an 8-hour window had higher chances of cardiovascular mortality compared to those who spread their meals over 12–14 hours.

 

 

What the study found

 

Researchers looked at data from over 19,000 adults in the US and discovered a striking trend - those who crammed all their meals into less than 8 hours a day faced a 135 per cent higher risk of dying from heart disease compared to people who ate over a more balanced 12–14 hour period. Put simply, while short fasting windows may help shed a few kilos, the study warns they could also take a toll on heart health in the long run.

 

Victor Wenze Zhong, the lead researcher for the US-China study from Shanghai Jiao Tong University, warned that people should be very cautious about sticking to a short eating window for a long time.

 

Researchers are still unsure why shorter eating windows may raise the risk of heart-related deaths. Some possible reasons include nutrient gaps, disruption of the body’s internal clock, or overeating during the eating window. For people with diabetes, fasting could also lead to dangerous blood sugar fluctuations.

 

"Skipping meals intermittently can foster unhealthy eating habits that impair immunity and impact overall health. Hormone imbalance, especially involving cortisol, insulin, and hunger-controlling hormones, often develops and further impairs metabolic health. Over time, these imbalances increase the risk of metabolic syndrome, obesity, cardiovascular disease, and other chronic disorders," said Dr Srishti Goyal, dietician, Ujala Cygnus Group of Hospitals.  

 

What experts say

 

“There have been some recent studies, including this joint study, that suggested short eating windows might increase the risk of heart problems and even death. But this study has been widely criticised for its design and methods, so it cannot be considered conclusive. Currently, there is no strong evidence that intermittent fasting harms the heart. In fact, it may help by reducing calorie intake and helping control obesity, which is a major cause of heart disease,” said Dr Dhiman Kahali, cardiologist, BM Birla Heart Hospital.

 

Adding to the discourse, Dr Prashant Pawar, consultant interventional cardiology, Fortis Hiranandani Hospital, said, "The available evidence is limited and has only addressed a subset of cardiovascular risk factors. Important questions remain unanswered, such as the optimal duration of fasting periods, the best timing during the day, the role of different food types, the degree of calorie restriction required, and how long one should adhere to fasting. Additionally, most studies lack comprehensive long-term data, which makes it essential to interpret findings with caution.”

 

Other hidden risks

 

Nutrient deficiencies can arise with intermittent fasting if your eating window is too short or your meals lack variety. 

 

"Intermittent fasting does pose a risk of nutrient shortfalls due to the risk of not meeting dietary needs, or poor balancing of dietary intake when you don't eat frequently. A decrease in meal frequency means decreased necessary intake of micronutrients, which are vitamins, like A, D, E, K, B-complex, minerals, calcium, iron, zinc, and protein for muscle maintenance and immune function. To prevent deficiencies, meals should be specifically planned with varied, nutrient-rich foods, staying hydrated, not taking excessive calories from food, and consuming adequate supplementation with medical guidance are vital for maintaining nutritional and metabolic homeostasis," said Dr CC Nair, internal medicine specialist, Lilavati Hospital & Research Centre.

 

Talking about impact on women, Dr Nair said, "Intermittent fasting has significant implications for the menstrual cycle and fertility in women, particularly in cases with longer fasting durations or inadequate caloric intake. It inhibits the hypothalamic secretion of gonadotropin-releasing hormone (GnRH), ultimately leading to downstream reductions in luteinizing hormone (LH) and follicle-stimulating hormone (FSH), important for ovulation and menstrual cycle control. This hormonal disruption can result in irregular cycles, amenorrhea, or reduced fertility. Elevated cortisol from energy restriction may further impair ovarian function."

 

Who should avoid intermittent fasting

 

Experts recommend consulting a doctor before starting intermittent fasting if you fall into any of these groups:

 

• History of eating disorders – Fasting can trigger unhealthy patterns like food obsession or binge eating.
• Pregnant or breastfeeding women – Higher nutritional needs make fasting risky for both mother and baby.
• People with diabetes or blood sugar issues – Fasting may cause dangerous sugar spikes or drops, especially with medication.
• People with hypertension or low blood pressure – Extended fasting can worsen symptoms like dizziness, weakness, and fainting.
• Athletes or highly active individuals – Fasting may reduce energy, slow recovery, and increase muscle loss.
• People on certain medications – Some medicines require food for absorption and safety.

 

Fasting works best in balance, not extremes

 

Dr Kahali shares that fasting should be done in moderation. “An occasional 24-hour fast or following a structured window can help reduce calories and manage weight. But it should be balanced with a healthy diet that includes plenty of fruits, vegetables, greens, some protein, and fewer carbs,” he said.  

 

“Avoid extreme practices like prolonged fasts or strict diets such as keto for long periods. Always pair fasting with moderate exercise, like regular walking, which supports heart health without putting too much strain on the body,” he added.

 

Dr Pawar added to this, “Those considering intermittent fasting should do so under medical guidance and after appropriate health screening. Personalization of the eating window and ensuring adequate nutrition during non-fasting periods are also key to minimizing potential risks.”

   

For more health updates, follow #HealthwithBS

This report is for informational purposes only and is not a substitute for professional medical advice.