Intermittent fasting has become the go-to health trend for weight loss, better metabolism, and even longevity. But what if your eating window is too short? CMC Vellore-trained, Dr Sudhir Kumar recently opened up about a new study conducted in the USA that has thrown a curveball into the fitness conversation, suggesting that fasting within an extreme 8-hour window might do more harm than good—especially for your heart. The expert has weighed in on these findings, and it may make you rethink your fasting plans.
The study that started it all
Researchers studied the eating patterns of nearly 20,000 adults in the US, tracking them for over 8 years. They compared different fasting windows—from less than 8 hours to more than 16 hours—and examined how these habits were linked to deaths from any cause, heart disease, and cancer. The results were eye-opening: those who squeezed all their meals into under 8 hours a day had more than double the risk of dying from cardiovascular disease compared to those who ate across 12–14 hours.
What the data really says
While these numbers are striking, Dr. Sudhir Kumar pointed out that the study has its limitations. It was observational, which means it shows association but not causation. In other words, fasting itself may not be directly to blame. Factors like diet quality, pre-existing illnesses, and even errors in self-reported data could have influenced the outcome. For example, someone with a chronic illness might naturally eat less often, making it look like fasting is the cause when it isn’t.
Why moderation is key
The study raises an important reminder: balance matters. The doctor shared that instead of cramming meals into a rigid 6–8-hour slot, a more moderate fasting window of 10–12 hours could be safer while still offering health benefits.
Who should be cautious
Intermittent fasting isn’t a one-size-fits-all solution. People with heart disease, diabetes, the elderly, or anyone on multiple medications should consult a doctor before attempting strict fasting routines. And if fasting makes you feel dizzy, fatigued, or leads to irregular heartbeats, it’s a clear sign your body isn’t adapting well.
The bigger picture
Intermittent fasting can absolutely help many people, but extreme versions may come with hidden risks. Instead of chasing quick fixes, the doctor recommends focusing on a balanced diet, a reasonable eating window, and long-term sustainable habits could be a healthier way forward.
The study that started it all
Researchers studied the eating patterns of nearly 20,000 adults in the US, tracking them for over 8 years. They compared different fasting windows—from less than 8 hours to more than 16 hours—and examined how these habits were linked to deaths from any cause, heart disease, and cancer. The results were eye-opening: those who squeezed all their meals into under 8 hours a day had more than double the risk of dying from cardiovascular disease compared to those who ate across 12–14 hours.
What the data really says
While these numbers are striking, Dr. Sudhir Kumar pointed out that the study has its limitations. It was observational, which means it shows association but not causation. In other words, fasting itself may not be directly to blame. Factors like diet quality, pre-existing illnesses, and even errors in self-reported data could have influenced the outcome. For example, someone with a chronic illness might naturally eat less often, making it look like fasting is the cause when it isn’t.
Is Intermittent fasting (IF) with an 8-hour eating window Risky for Your Heart?
— Dr Sudhir Kumar MD DM (@hyderabaddoctor) August 25, 2025
▶️A new study has raised questions about the safety of very short eating windows, such as those promoted in extreme forms of intermittent fasting.
The Study at a Glance
▶️Researchers analyzed data…
Why moderation is key
The study raises an important reminder: balance matters. The doctor shared that instead of cramming meals into a rigid 6–8-hour slot, a more moderate fasting window of 10–12 hours could be safer while still offering health benefits.
Who should be cautious
Intermittent fasting isn’t a one-size-fits-all solution. People with heart disease, diabetes, the elderly, or anyone on multiple medications should consult a doctor before attempting strict fasting routines. And if fasting makes you feel dizzy, fatigued, or leads to irregular heartbeats, it’s a clear sign your body isn’t adapting well.
The bigger picture
Intermittent fasting can absolutely help many people, but extreme versions may come with hidden risks. Instead of chasing quick fixes, the doctor recommends focusing on a balanced diet, a reasonable eating window, and long-term sustainable habits could be a healthier way forward.
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Can intermittent fasting secretly harm your heart? CMC Vellore doctor point outs risks
