Fasting for Health or Disease
Janet Maendel DO(EUR), DNM
Fasting has existed for thousands of years, woven into spiritual traditions, cultural practices, and natural rhythms of human life. Only recently has modern research begun to uncover why fasting appears so beneficial across so many systems of the body. What was historically viewed as a period of rest, recovery, and reset is now understood as a powerful metabolic intervention capable of influencing hormones, inflammation, immune regulation, cognition, and long-term disease risk.
The Benefits of Fasting
One of the most profound effects of fasting is its impact on metabolic health. By intentionally limiting food intake for structured periods of time, the body shifts away from relying on glucose and begins using stored fat for fuel. While weight loss may occur, the more clinically relevant benefit is improved insulin sensitivity and enhanced metabolic flexibility. As insulin becomes more efficient, blood sugar stabilizes and the risk of chronic conditions—such as Type 2 diabetes, cancer, cardiovascular disease, and hormonal imbalances—begins to decline.
Fasting also triggers cellular repair through the process of autophagy, where the body breaks down damaged cellular components and recycles them for future use. This natural detoxification process reduces oxidative stress, prevents the buildup of dysfunctional proteins, and supports the removal of pre-cancerous or weakened cells. Many researchers consider autophagy to be one of the key reasons fasting can reduce long-term disease risk.
Brain health is another area where fasting exerts measurable benefits. Fasting increases production of brain-derived neurotrophic factor (BDNF), a protein essential for neuron protection, growth, and repair. Higher BDNF levels are associated with improved memory, enhanced cognitive function, and reduced risk of neurodegenerative diseases such as Alzheimer’s and Parkinson’s. Cardiovascular health also improves, with reductions seen in blood pressure, LDL cholesterol, triglycerides, and inflammatory markers—factors that dramatically influence heart disease risk.
Longevity research has shown promising connections between fasting, reduced oxidative stress, improved metabolic function, and enhanced cellular repair. While fasting alone is not a guarantee of extended lifespan, it clearly supports the internal conditions that promote healthier aging.
Types of Fasting
Fasting takes many forms, each with its own structure and metabolic effect. The most common is intermittent fasting, where the final meal of the day is eaten in the mid- to late afternoon and food is withheld for 12–18 hours. Variations such as the 16/8 method, the 5:2 method, 24-hour fasts, alternate-day fasting, extended fasts, and time-restricted eating modify fasting and feeding windows but share the same underlying principle: strategic rest for the digestive and metabolic systems.
Cyclic or periodic fasting alternates structured fasting with normal eating in a rhythm intended to be more sustainable long term. Because the body does not adapt to continuous calorie restriction, metabolic rate remains stable, and fat-burning pathways remain active. Cyclic fasting also supports hormonal balance, appetite regulation, and improved leptin and ghrelin signaling.
For women who menstruate, fasting can be synchronized with the menstrual cycle. The follicular phase, where estrogen naturally rises, tends to be more compatible with fasting, while the luteal phase often benefits from more nourishment to support progesterone production and stabilize mood and energy. When used appropriately, cycle-aware fasting becomes a powerful tool for hormonal balance.
Metabolic Flexibility and Individual Variability
Not everyone can fast safely. A degree of metabolic flexibility—the ability to switch between glucose and ketone metabolism—is necessary for fasting to be comfortable and effective. Individuals with poor metabolic health, insulin resistance, high stress, or disrupted sleep may initially struggle to fast. In these cases, fasting should be introduced slowly under the guidance of a trained practitioner. Over several months, as nutrition improves and metabolism stabilizes, fasting windows can often be extended with greater ease.
Fasting and Cancer
Cancer research has increasingly focused on metabolism, revealing that cancer cells rely heavily on glucose and are less adaptable to metabolic stress. Fasting creates an internal environment that is more challenging for cancer cells to thrive in while simultaneously strengthening the resilience of normal cells.
Although fasting is not a cure for cancer, evidence suggests it may enhance the effects of conventional treatments. When fasting precedes chemotherapy, cancer cells—already under metabolic strain—may become more vulnerable to treatment, while healthy cells activate protective mechanisms. This phenomenon, called differential stress resistance, helps explain why patients who fast before chemotherapy often report fewer side effects, including nausea, fatigue, and gastrointestinal discomfort.
Fasting also inhibits cancer growth by arresting the cancer cell cycle, reducing available glucose, lowering insulin and IGF-1 (key drivers of cellular proliferation), and promoting oxidative stress within cancer cells. Autophagy, heightened during fasting, supports the removal of damaged cells and may help prevent cancer progression. Furthermore, fasting enhances immune function and improves surveillance, enabling the body to better identify and eliminate abnormal or malignant cells.
Because cancer is highly individualized, fasting must be used cautiously. Elderly patients, children, individuals with cachexia, or those having difficulty maintaining body weight may not be candidates for fasting. Any fasting intervention for patients with cancer should be supervised by a knowledgeable clinician who can monitor symptoms, labs, and overall constitutional strength.
Individualization and Safety
The benefits of fasting vary widely based on age, health status, metabolic function, stress levels, and underlying disease. For most people, fasting—when paired with nutrient-dense eating, adequate hydration, restorative sleep, and stress reduction—can significantly improve health. For others, particularly those with complex medical conditions, fasting may require modification or may not be appropriate at certain stages of illness or treatment.
A Powerful Tool for Wellness and Resilience
Fasting offers an accessible, biologically grounded strategy for improving metabolic health, supporting cellular repair, reducing inflammation, and lowering chronic disease risk. When integrated thoughtfully and safely, it can complement therapies for a variety of conditions, including cancer. As research continues to expand our understanding of its mechanisms, fasting remains a profound tool—one that reconnects the body to ancient rhythms of rest, restoration, and resilience.