Fasting has long played a role in major religions, but we did not begin to understand it from a scientific standpoint until Yoshinori Ohsumi, a Japanese cell biologist, discovered how cells recycle and renew themselves during fasting, for which he was awarded a Nobel Prize in 2016. Since then, multiple clinical trials have proven the health benefits of intermittent fasting (IF).

How Intermittent Fasting Works

IF influences the body's blood sugar control, energy production, gut bacteria load and hormone levels. When abstaining from food for a period of time, the body begins to rely on fat stores for cellular fuel. This shift in energy metabolism also allows for enhanced autophagy, a process that removes damaged cellular components and promotes cellular renewal and repair.

Regimen Types

• Time-Restricted Feeding (TRF) involves limiting the daily eating window to a specific period, typically eight to 10 hours, followed by a fasting period of 14 to 16 hours. This regimen can be followed daily or limited to a few days per week.
• Alternate-Day Fasting involves alternating between days of normal caloric intake and days of severe calorie restriction.
• 5:2 Diet entails consuming a normal diet for five days and restricting calorie intake to 500 to 600 calories on two non-consecutive days.
• The Warrior Diet involves fasting for 20 hours followed by a four-hour eating window, typically in the evening.

Selecting a Regimen

All forms of IF have similar health benefits. Each approach has its own merits, and it is crucial to choose the one that aligns with personal goals, lifestyle, fasting tolerance and overall well-being. Before adopting an IF routine, it is important to consult with a healthcare professional.

The easiest approach for many people is TRF, where eating stops at 9 p.m., breakfast is limited to coffee or tea without sugar or milk and eating resumes at noon. TRF has been shown to have similar benefits if followed every day or even just three days per week.

Fasting for a minimum of 12 hours provides some benefits, but a fasting period of 15 hours or more often yields greater benefits. The best fasting hours depend on an individual’s work schedule and goals. Some individuals may find it more convenient to begin their fast in the evening and skip breakfast, while others prefer to omit dinner and have an early lunch, thus extending their overnight fast. The most critical factor is finding a pattern that can be maintained consistently.

Benefits of Intermittent Fasting

Intermittent fasting has been associated with numerous health benefits, including enhanced cognitive performance, weight loss, reduced cardiovascular risk factors and better blood sugar control.

A study published in Cell Metabolism suggests that IF might correct circadian rhythm disruptions, which are believed to play a role in the progression of Alzheimer's disease. The researchers found that IF improves memory and reduces the accumulation of fibrous amyloid proteins in the brain. Other studies have also found that IF enhances memory, attention, brain processing speed and cognitive function.

Multiple randomized clinical trials have shown that intermittent fasting is effective for modest weight loss, varying from five to 15 pounds, as well as reductions in waist circumference, body mass index and cardiometabolic risk factors. 

IF is a safe dietary option to improve several markers of cardiometabolic health. A meta-analysis of 130 randomized clinical trials of subjects following all forms of IF showed improvements in insulin sensitivity, plus improvements in weight, cholesterol profiles, fasting blood sugar levels and blood pressure control. These findings suggest that IF is effective in helping to prevent heart disease.

An article in the Journal of Restorative Medicine highlighted the potential benefits of IF in preventing and treating cancer, although more research is needed. The authors noted that IF can promote recycling of cells, enhance DNA repair in normal cells, improve cell regeneration in tissues and protect against the toxic effects of chemotherapy.

Safety and Other Considerations

Intermittent fasting is generally considered safe for most healthy individuals. However, young children, pregnant or breastfeeding women, and individuals with epilepsy, a history of eating disorders and those taking medications that can lower blood sugar levels should exercise caution or avoid fasting altogether.

While intermittent fasting can offer numerous benefits, some individuals may experience increased hunger and food cravings, poor sleep quality, an excessive drop in blood sugar levels in individuals prone to hypoglycemia and adverse effects on hormonal balance, especially for women that are menstruating.

Steven Masley is a physician, nutritionist, trained chef, clinical professor at the University of South Florida and creator of health programs for public television. He is the author of The 30-Day Heart Tune-Up. Learn more at DrMasley.com.