Intermittent fasting is a topic that’s not starving for attention. In both conventional and alternative medical circles, the best methods of fasting and their associated health benefits are generating plenty of discussion. Even a famous yogi has addressed this trend, saying it is simply the world catching on to what yogis have practiced for centuries.
Fasting requires a break from food, but the duration and types of fasting can differ. Intermittent fasting (IF) isn’t strictly defined, but it typically involves going without food for a period of 16 to 24 hours and then returning to normal eating.
Because the body uses a significant amount of energy to digest food, abstaining from food conserves that energy and allows the body time to regulate and cleanse itself. IF seems to fit modern lifestyles of work or study because it is easier to do than fasts that last more than one day.
Dr. Dean Ornish, clinical professor of medicine at the University of California, San Francisco, and Dr. Valter Longo, director of the University of Southern California’s Longevity Institute, say that intermittent fasting can reduce occurrence and even reverse some of the chronic diseases that plague modern society, such as cardiovascular disease, diabetes, and cancer.
Johns Hopkins University neuroscientist Dr. Mark Mattson agrees. After studying IF for 25 years, he has concluded that the human body evolved to survive without food for many hours or days due to necessity. In prehistoric times, humans were hunters and gatherers, and it took a lot of time to procure a meal.
After studying intermittent fasting for 25 years, [Dr. Mark Mattson] has concluded that the human body evolved to survive without food for many hours or days due to necessity.
Even as recently as 50 years ago, chronic illnesses were not as prevalent as today. Increased consumption of processed foods high in sugar, salt, and unhealthy fats, along with decreased physical activity and a sedentary lifestyle have contributed to a rise in obesity, diabetes, and cardiovascular diseases. People generally ate smaller portions and went to bed when it got dark. More time was spent working and playing outdoors, leading to a more active lifestyle overall.
The advent of modern conveniences, particularly television and computers, dramatically lowered the amount of time people spend outside. There is a common thread throughout health and fitness texts that people should sit less and eat less. Yet, most people can’t deny that they sit and snack more than is healthy and have occasionally had bouts of late-night noshing in front of the television.
While IF methods promote healthful foods and drinks, they aren’t focused as much about what people eat but when. The excitement from experts over the evidence thus far suggests that it may be worth going to bed hungry now and then, because in addition to indications of potentially reducing levels of chronic disease, IF results imply improved overall health and increased longevity.
Common Intermittent Fasting Methods
16/8 Method (Leangains Protocol): The fasting window is 16 hours of fasting, followed by an 8-hour eating window. Many people skip breakfast and eat their first meal at noon, then finish their last meal by 8 p.m. Variations on this can use any 8-hour eating window. Developed by Martin Berkhan, Swedish nutritional consultant and personal trainer, this IF method is one of the first to go mainstream.
5:2 Diet: In a week, two non-consecutive days of reduced caloric intake (500 to 600 calories), are intermixed with the remaining five days of normal eating. This is a flexible plan that can be adjusted weekly.
Eat Stop Eat: Designed by weight-loss guru and IF advocate Brad Pilon, the Eat-Stop-Eat plan is designed to have a complete break from food for 24 hours once or twice per week. For example, eat normally until 6 p.m. on Friday, fast until 6 p.m. on Saturday, and then go back to a regular eating pattern. Pilon points out that even one fast per week can be beneficial, but he does not recommend more than two. He also says it’s crucial to ensure adequate hydration during the fast.
Alternate-Day Fasting: An intense method of IF, alternate-day fasting is just that: Eat a normal diet one day and either completely fast or have one small meal (less than 500 calories) the next day.
Spontaneous Meal Skipping: This IF method is flexible and allows one to skip meals when convenient or when not feeling hungry. It can be applied occasionally, without following a schedule.
Potential Health Benefits of Intermittent Fasting
IF has been shown to have health benefits such as delayed onset of age-related diseases and increased lifespan. At the Massachusetts Institute of Technology (MIT), researchers have found that fasting boosts the regenerative abilities of intestinal stem cells in mice, which can help the intestine to recover from inflammation or injury.
IF [intermittent fasting] has been shown to have health benefits such as delayed onset of age-related diseases and increased lifespan.
It’s important to note that “health benefits seen in mice” are sometimes touted simply as “health benefits” and the reader might believe these benefits apply to humans. While studies on mice can show promise for future results in humans, it may not be the case with all health benefits. Other health benefits attributed to fasting are sometimes first-person reports and testimonials to programs. This is not to say they aren’t true, but they are not from scientific studies conducted on a large number of people over a length of time and compared to a control group.
The following health benefits are believed by many to be reasonable outcomes of IF.
Weight Loss and Fat Loss: IF reduces calorie intake by limiting the eating window, which can lead to weight loss. It also promotes fat burning by lowering insulin levels during fasting periods.
Improved Metabolic Health: Fasting can lead to improved insulin sensitivity, lower blood sugar levels, and reduced inflammation, all of which are beneficial for metabolic health.
Autophagy: Fasting for 24 to 48 hours can trigger autophagy, a process in which the body cleans out damaged cells and regenerates new ones. This process is thought to protect against diseases like cancer and Alzheimer’s. In studies done on mice, Longo saw that healthy cells survive better than cancer cells in fasting conditions. He hypothesizes that in evolving to divide so rapidly, cancer cells gave up other evolutionary adaptations, such as surviving in the absence of nutrition.
Heart Health: IF may help improve various risk factors for heart disease, including cholesterol levels, blood pressure, and inflammatory markers.
Brain Health: Fasting may enhance brain function by increasing the production of brain-derived neurotrophic factor (BDNF) and reducing the risk of neurodegenerative diseases.
Longevity: Animal studies suggest that intermittent fasting may extend lifespan, potentially due to its effects on cellular repair processes, inflammation, and metabolic health.
Chemotherapy: Researchers found that people who fasted for 72 hours before chemotherapy treatments underwent lower toxicity and a lighter effect on bone marrow due to the treatment. This could be a helpful adjunct to chemotherapy treatments if only to lessen the dire side effects for patients.
Researchers found that people who fasted for 72 hours before chemotherapy treatments underwent lower toxicity and a lighter effect on bone marrow due to the treatment.
Potential Risks
Many experts are cautioning that people shouldn’t move too fast toward fasting because research studies involving IF with humans have been short and small. These studies have experienced a high percentage of dropouts, which could be a sign of the difficulty of IF. A 2020 systematic review of studies done on forms of IF indicates promise for the treatment of obesity; however, the review also adds that more long-term research into intermittent fasting is necessary to positively confirm other health benefits in humans. Still, even the small body of research has many practitioners excited about a diet that holds promise for incredible health benefits.
In a study of mice published in Nature in August 2024, MIT researchers have now identified the pathway that enables the enhanced regeneration of intestinal stem cells, which is activated once the mice begin “refeeding” after the fast. They also found a downside: When cancerous mutations appeared during the regenerative period, the mice were more likely to develop early-stage intestinal tumors. “Having more stem cell activity is good for regeneration, but too much of a good thing over time can have less favorable consequences,” says Omer Yilmaz, an MIT associate professor of biology, a member of MIT’s Koch Institute for Integrative Cancer Research, and the senior author of the new study. While this initially seems dismal news for IF, it is the results seen in mice and could lead to greater refinement of fasting windows. Perhaps the ideal regeneration window is such that the results will not cause increased likelihood of cancer, or the introduction of mutations will be able to be avoided. The results may or may not transfer to human studies.
Other Considerations
For those who want to try IF, it is recommended to check with a medical provider first. Dr. Frank Hu, chair of the department of nutrition at the Harvard T.H. Chan School of Public Health, points out that those with a history of eating disorders, pregnant or breastfeeding women, individuals being treated for high blood pressure, have heart or kidney disease, or those with unstable blood sugar levels (such as with diabetes) should not fast. In these people, fasting could cause dangerously low blood sugar or electrolyte imbalances.
It’s important that during eating windows, one consumes nutrient-dense foods that are rich in protein, fiber, and healthful fats. If the focus is solely on caloric intake without regard to nutrition, it could lead to deficiencies. And while the intermittent faster may be ready to eat a huge meal when breaking a fast, go slow. “It’s better to spread those calories over your next two meals,” advises hepatologist Nizar Zein, MD, of the Cleveland Clinic. “This will help you avoid rapid changes in blood sugar and the fatigue associated with consuming a large amount of food.”
It’s important that during eating windows, one consumes nutrient-dense foods that are rich in protein, fiber, and healthful fats.
During the fasting window, it’s crucial to maintain hydration. Drink water (plain or flavored with lemon, lime, or cucumber), black coffee, herbal and green teas, sparkling water, or any other drink that is close to zero calories.
Some people may experience hunger, irritability, headaches, or difficulty concentrating during fasting periods. These effects often diminish as the body adapts to the eating pattern. Still, it is helpful to avoid thinking about food or being at functions where food is the focus. It’s also advised to avoid strenuous activities while fasting.
Fasting schedules can sometimes interfere with social and family activities, making it challenging to maintain long-term. To help with success, make the calories count by selecting nutrient-dense foods that are rich in fiber, healthful fats, and protein (avocado, beans, eggs, fish, lentils, nuts). Filling foods that are low calorie are also helpful (fruits with high water content, raw vegetables, popcorn). Any time fewer calories are to be eaten, it’s a great idea to season meals generously with herbs and spices. Full flavors can reduce feelings of hunger.
Conclusion
The evidence is still coming in, but many experts on nutrition and longevity believe that intermittent fasting can be an effective and flexible dietary approach for improving health, managing weight, and increasing lifespan. It’s important to consult with a healthcare provider, especially if there are any preexisting health conditions. If the green light is given, choose an IF method that fits your lifestyle and approach it with a focus on balanced nutrition and overall well-being. Eat fresh, local foods and stay hydrated. It’s also a good idea to enlist the support of friends or family, as society’s focus-on-food can make it difficult to endure very low-calorie days over the long term.
*Julie Peterson writes science-based articles about holistic health, environmental issues, and sustainable living from her organic farm in Wisconsin.
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