In the world of diets, intermittent fasting (IF) has gained global attention and a stream of followers. A new study, with a sample of over 19,000 individuals, has however, found that such individuals who restrict the eating window to under eight hours a day have a much higher risk of cardiovascular issues compared to those who eat within a typical window of 12-14 hours.
Published in Diabetes and Metabolic Syndrome: Clinical Research and Reviews, the study is the first one to highlight this cardiovascular risk and the authors warrant further research.
An accompanying editorial by Dr Anoop Misra, Editor-in-Chief, underscores the need for balance despite IF’s proven benefits such as weight loss, improved insulin sensitivity, and better lipid control. He cautions that IF is not a one-size-fits-all solution and should be practiced for a short time under medical supervision. Risks include nutrient deficiencies, hypoglycaemia in diabetics, and frailty in older adults, in addition to the cardiovascular harm indicated by the aforementioned study.
Though conducted in the USA, the study has global implications across demographic and lifestyle subgroups, though it offers little evidence of direct causation with mortality.
Varsha Gorey, senior clinical dietician at the Apollo Hospital, Navi Mumbai, noted that while IF is supported by a scientific rationale, such as the reduction of oxidative stress, which in turn delays conditions like Alzheimer’s disease and some pilot studies suggesting potential improvements in cognition and mood.
However, the magnitude of benefits varies by protocol, adherence, and individual health profile. Overly strict fasting windows can backfire, triggering hunger binges, headaches, and hormonal disruptions, particularly in women.
Dr. Balakrishna G.K., HOD and Senior Consultant Internal Medicine, Gleneagles BGS Hospital, Kengeri, Bengaluru, observed that not everyone eats less with a shorter window. Some may overcompensate and thus, overeat, erasing gains. Prolonged fasting can deplete muscle, strain organs, and destabilise blood sugar, making it especially dangerous for people with diabetes.
He said that while the body could adapt well to fasting, doing it for long hours, especially without medical advice, may place undue stress on different organs. For instance, the brain uses glucose for fuel. Going long stretches without food could lead to irritability, poor focus, dizziness, and at times, confusion or fainting. If the body stays undernourished, memory and thinking can be affected over time. Electrolyte imbalances (like low potassium or magnesium) can directly affect heart rhythm and function. Muscle loss, including the heart muscle, is another long-term risk if protein intake is insufficient.
Dr Subrata Das, Senior Consultant and Head of Department, Internal Medicine and Diabetology, Sakra World Hospital, Bengaluru, says wild blood glucose swings from extreme fasting cause lasting harm to organs, raising oxidative stress and inflammation.
Neurological effects are also important. According to Vedika Premani, Clinical Dietician, Sir H.N. Reliance Foundation Hospital, Mumbai, lengthy fasts push the brain to focus obsessively on food, increasing cravings and risk of binge-eating later in the eating window. For some, IF becomes a cycle of deprivation and excess, undermining stable, healthy eating.
Dr Sunil Rana, Associate Director and Head, Internal Medicine, Asian Hospital, Faridabad, identified the Achilles heel. While Short-term fasting may help control weight and sugar, rigid, long-term regimens often result in slower metabolism, hormonal imbalances, and a greater risk of muscle and bone loss, especially in women and the elderly.
It can also lead to high levels of cortisol- the stress hormone, which can in turn induce anxiety, disrupt sleep, and promote belly fat, going straight against weight-loss efforts. Deficiencies in nutrients are another concern, with calcium, vitamin D, iron, and essential fatty acids frequently being left out of restricted eating periods. Women can develop menstrual irregularities and reduced bone density, while older adults can experience accelerated muscle loss.
With fasting traditions rooted in culture, India has quickly adopted IF in urban centres. But as evidence evolves, experts urge to balance enthusiasm with caution. Fasting should complement, not replace wholesome nutrition, daily activity, and sleep.
This landmark study serves as a wake-up call. A very short eating window can sharply elevate heart risk, outweighing many of the presumed benefits. Individualisation, medical supervision, and moderation are the watchwords for anyone considering IF. Until further large-scale trials clarify who benefits and who is put at risk, caution, rather than wholesale adoption, is warranted.