Fasting has evolved from a religious ritual into a popular fitness trend. From 16:8 diets to one-meal-a-day plans, the promise is simple: eat less often, lose weight faster, feel better. For many, it works in the short term. However, a growing body of research is now asking a harder question: What happens when the body is pushed too far for too long? New evidence suggests that extreme or poorly planned fasting may not just affect energy levels but could also place stress on the heart.
The Rise of Fasting in Fitness Culture
Scroll through any fitness feed, and fasting appears almost non-negotiable. It is often packaged as a clean, science-backed way to burn fat and reset metabolism. Earlier studies did show benefits, including better blood sugar control, lower cholesterol, and modest weight loss. That helped fasting gain credibility beyond fad diets. Yet, the trend has taken a sharper turn. Eating windows are shrinking. What began as 12-hour gaps has moved to 8 hours or less, sometimes even one meal a day. That is where the concern begins to build.
What the Latest Research Is Warning
An analysis of over 20,000 adults found that people who ate within an 8-hour window or less had a significantly higher risk of dying from cardiovascular causes compared to those who spread meals across 12 to 16 hours. In some groups, the risk was reported to be up to 91% higher. These numbers do not mean fasting is dangerous for everyone, but they challenge the popular belief that shorter is always better.
How Fasting Can Quietly Stress the Heart
The body does not simply switch modes without consequences. It adapts, and sometimes that adaptation comes at a cost. Dr. Dibya Ranjan Behera explains, "The potential negative health effects of prolonged fasting may cause the body to go through rapid changes in blood sugar levels, release of stress hormones into the bloodstream, and an increase in lipid levels; all of which can be harmful to the heart." Long gaps between meals can cause blood sugar dips, followed by sudden spikes. Stress hormones like adrenaline and cortisol may rise, making the heart beat faster or irregularly.
Dr. Dithesh M notes, "Long gaps between meals can trigger fluctuations in blood sugar, electrolytes, and stress hormones. These changes may increase heart rate variability and, in susceptible individuals, provoke palpitations or irregular heart rhythms." Then there is dehydration. Skipping meals often means skipping fluids too. Electrolytes like potassium and magnesium may fall. These minerals are essential for the heart's electrical rhythm. Dr. Sunil Roy T N adds, "Electrolytes may fall, disrupting the electrical signals that keep the heart beating steadily. Dehydration reduces blood volume, forcing the heart to work harder." Rapid shifts in blood sugar, dehydration, and electrolyte imbalance can strain the cardiovascular system, especially in vulnerable individuals.
Who Should Be More Careful
Not everyone faces the same level of risk. For a healthy adult, occasional fasting may feel manageable. But certain groups need to think twice. People with diabetes, high blood pressure, or existing heart disease fall into a higher-risk category. Those taking medications such as diuretics or beta-blockers may also respond differently to fasting. Dr. Dithesh M warns, "People with underlying heart disease, diabetes, or those on medications may be particularly vulnerable." Even otherwise healthy individuals should not ignore warning signs. Persistent fatigue, dizziness, chest discomfort, or palpitations are not normal side effects. They are signals that the body is under strain.
The Emotional and Physical Toll
Fasting is often framed as discipline. But when taken to extremes, it can lead to a cycle of restriction and exhaustion. Low energy, irritability, reduced exercise capacity, and even fainting spells can creep in. Over time, this can affect daily functioning and mental well-being. There is also a subtle pressure to push through discomfort in the name of fitness. That mindset can delay people from seeking help when something feels off.
Finding a Safer Balance
Fasting is not inherently harmful. It becomes risky when it is rigid, extreme, or disconnected from individual health needs. A balanced approach matters more than a strict schedule. Eating windows should not compromise nutrition, hydration, or overall well-being. Dr. Dibya Ranjan Behera advises, "Consistency, balance, and medical factors play a role. It is important to consult with your physician to develop a plan that will suit your unique medical needs." Simple steps can make a difference:
- Avoid very short eating windows without supervision
- Stay well hydrated throughout the day
- Focus on nutrient-rich meals, not just fewer meals
- Pay attention to warning signs instead of ignoring them
Dr. Dithesh M sums it up clearly, "Fasting is not a one-size-fits-all solution. Listening to your body—and your doctor—can help ensure that dietary choices support, rather than compromise, long-term heart health."
Medical Experts Consulted
This article includes expert inputs shared with TOI Health by: Dr. Dibya Ranjan Behera, Consultant - Interventional Cardiology, Manipal Hospital, Bhubaneshwar; Dr. Dithesh M, MBBS, MD, DrNB (Cardiology), FAGE, FAPSIC, KMC Hospital, Mangalore; Dr. Sunil Roy T N, Senior Consultant - Interventional Cardiology, Aster Medcity, Kochi. Their insights were used to examine the potential risks of fasting for fitness, highlight emerging concerns around its impact on heart health, and emphasize the need for a balanced, medically guided approach before adopting such practices.
